V. DISCUSSION
It is well understood from the literature that the physical and chemical
characteristics of water in any locality exerts their influence on the occurrence and
abundance of the biological components. Although physico-chemical properties
have an effect on the biological processes, many of them are subtle and intricate,
hence cannot be clearly understood. Among the various categories of water body,
it is in the brackish water environment such as estuary, where the magnitude of
influence of physico-chemical parameters on the biological resources is
comparatively higher which makes the environment more dynamic. A proper
understanding of any biological problem in the estuary is possible only if the
physical and chemical characteristics of the environment are properly
documented.
5.1. Meteorology 5.1.1. Rainfall
During the investigation, the study area experienced 3296.10 mm total
annual rainfall (Table 1). In the pre-monsoon season, May and April month
experienced moderate rainfall of 4.68%. During the monsoon season (June and
September months), study area received high rainfall of 89.52%. Whereas in the
post-monsoon season, (October and November) experienced a moderate rainfall of
5.99%. No rainfall was observed during the month of January, February and
March.
5.1.2. Air temperature The air temperature recorded during the period from January to December
2005 fluctuated from 25.64°C to 34.22°C (Table 2). The seasonal variation in the
air temperature revealed that the region exhibited three distinct temperature
regimes. The higher regime during pre-monsoon season and the lower regime
during south west monsoon season and third moderate regime in post-monsoon
season. Therefore from the data observed, it is revealed that air temperature
exhibited a trimodal seasonal oscillation. Similar seasonal fluctuation was
documented by Sahu (1981), Reddy (1982), Patil (1987), Puranik (1990), Ronald
(2001), Vijay Kumar (2002) and Chandrashekara (2004) while working on the
various brackish water environments along the coast of Dakshina Kannada and
Udupi district. In the present study, a trimodal seasonal oscillation could be due to
the observations made even during monsoon season. From the data, it is believed
that the intensity and the duration of south west monsoon winds by and large
control the air temperature in this region. However, the small drop in the air
temperature during the north east monsoon is also common.
5.2. Hydrography
5.2.1. Water temperature
The water temperature during the present study fluctuated from 23.30oC to
33.2oC with an annual range of 9.90oC (Table 3). Ansari et al. (1986) recorded an
annual range of 8.40oC in Mandovi-Zuari estuary. In the same estuary,
Krishnakumari et al. (2002) observed 29.78oC as a mean surface water
temperature. However, the highest range of 13.0oC was observed by Prabha Devi
(1994) in Coleroon estuary. Menon et al. (1977) recorded a range of 7.0oC
between highest and lowest water temperature in Mangalore waters. Patil (1987)
observed a range of 6.8oC between highest and lowest in Nethravati-Gurupur
estuary. In the same estuary, Vijay Kumar (2002) and Tripathi (2002) documented
an annual range of 5.50oC. Chandrashekara (2004) observed an annual range of
5.40oC in Sita-Swarna estuary. While comparing the annual ranges recorded by
various authors, it became evident that the water temperature fluctuated between
the maximum and minimum was high in Haladi-Chakra estuary. This increased
range could be due to the higher quantity of freshwater drainage from rivers to the
estuary or the intrusion of up welled waters in the estuarine basins from the
adjoining coastal waters. The other climatiological parameters in this region might
also have contributed for the high annual range of water temperature between
lowest and highest in the present study.
The seasonal variation of water temperature in Haladi-Chakra estuary
revealed a gradual increase in trend from February and reached a maximum in
May. The onset of monsoon brought down the water temperature to a very low
level during September. Gradual increase in water temperature during post-
monsoon season was observed at all the stations with a small drop in the month of
December. Thus from Figure 2, it is evident that the water temperature exhibited a
clear cut bimodal seasonal oscillation with two highs and two lows. Similar
seasonal variation observed by Bhat (1979), Patil (1987), Puranik (1990), Vijay
Kumar (2002) and Chandrashekara (2004) in various brackish water environment
of west coast of India.
5.2.2. Water pH
In the present investigation, the surface water pH exhibited a seasonal and
spatial variation. During pre-monsoon season, pH varied from 7.13 to 8.12 and in
monsoon season from 6.61 to 7.61. While during post-monsoon season, the
surface water pH fluctuated from 7.51 to 7.99. From the Table 4 and Figure 3, it is
clear that pH was high in May at all the stations. Similar high pH values were
observed by Puranik (1990), Ronald (2001) and Tripathi (2002) in Nethravati-
Gurupur estuary. The lower values of pH at all stations coincided with south west
monsoon season and the presence of freshwater throughout the estuarine basin due
to monsoon season. Kaliyamurthy (1976) observed minimum pH values during
south west monsoon season and opined that reduction in values were due to
presence of freshwater in the estuaries.
Several workers have been reported the lower values of pH during south
west monsoon season in the Nethravati-Gurupur estuary. Bhat (1979), Reddy
(1982) recorded a lowest pH of 6.4 during August. While Nagrajaiah (1981)
observed a low pH value of 7.01 during July. The lower values recorded in the
month of July during the present study is in agreement with the works carried by
various authors in the estuaries of Dakshina Kannada. A gradual increase in trend
during the post-monsoon season was observed in the present study. This increase
in trend could be due to the presence of seawater in the estuary. Similar
explanation was put forwarded by Patil (1987) and Puranik (1990). The spatial
distribution of surface water pH revealed generally higher values at stations
located in confluence region. While stations located away from the confluence
registered lower pH throughout the period of study. From the data gathered, the
pH values of surface water were not only found to be dependent on the season, but
also to the proximity to the sea.
5.2.3. Water dissolved oxygen
The composition of water along with temperature significantly influence
dissolution of atmospheric gases and its holding capacity. The situation gets
further complicated in estuarine environment, which is subjected to diel and tidal
variations. In the present investigation the surface dissolved oxygen content in this
estuary ranged from 0.0 to 7.81 mg/l with an annual range between highest and
lowest to be 7.81 (Table 5). Menon et al. (1977) and Bhat (1979) recorded an
annual range of 4.8 ml/l and 3.9 ml/l respectively in Nethravati-Gurupur estuary.
Puranik (1990) and Vijay Kumar (2002) have reported an annual range of 2.2 ml/l
and 5.97 ml/l respectively in the same estuary. Reddy (1982) observed a
difference of 2.69 ml/l between two extreme values in Mulki estuary. However,
Chandraskekara (2004) have registered an annual range of 3.70 mg/l in the Sita-
Swarna estuary, Udupi.
In the present study, the lowest dissolved oxygen of 0.0 mg/l was recorded
at two stations. While in other three stations was between 0.41 to 2.05 mg/l. This
low dissolved oxygen values have affected the annual range at a great extent. This
lower value of dissolved oxygen is perhaps being due to intrusion of up welled
waters. In the present study, dissolved oxygen of 0.0 to 0.41 mg/l was recorded at
station 1 located at the confluence and at station 3 and 5 located nearer to the
confluence. Whereas, stations located away from the confluence registered
comparatively higher values of dissolved oxygen. Manoj kumar (1988) observed
low oxygenated water in the Malpe estuary and opined that the low oxygenated
condition could be due to intrusion of up welled water. Reddy et al. (2005)
recorded dissolved oxygen content as low as 2.19 mg/l in the coastal waters of
Mangalore. The authors have related this low dissolved oxygen due to the
occurrence of Tsunami in Bay of Bengal in December 2004.
Except the low dissolved oxygen in the month of September the surface
water dissolved oxygen exhibited normal spatial and seasonal variation. During
the pre-monsoon season, the dissolved oxygen content was found to reduce
gradually reaching the lowest in the month of May. This is found to be quite
contradictory to the observations made by De’souza (1977), Patil (1987), Puranik
(1990) and Vijay Kumar (2002). This change in the present study could be
directly related to the disturbances found in the Arabian Sea due to Tsunami
effect.
With the onset of monsoon there was a sudden rise in the dissolved oxygen
content reaching its peak in June and July. There after the dissolved oxygen
content decreased at all stations. Varma et al. (1975) have observed the maximum
dissolved oxygen content during the south west monsoon season in Mandovi
estuary. Qasim and Gupta (1981) observed a large changes in dissolved oxygen
content during south west monsoon season in Mandovi-Zuari estuary and opined
that oxygen cycle is closely related to seasonal changes. Bhat (1979) and Reddy
(1982) recorded higher values of dissolved oxygen during the monsoon season in
Nethravati-Gurupur estuary. However, Patil (1987) and Puranik (1990)
documented moderate values of dissolved oxygen during monsoon season in the
same environment.
The gradual increase in the dissolved oxygen content was observed from
October to January, forming a secondary peak. The seasonal fluctuation of
dissolved oxygen from the data revealed it exibit by and large bimodal seasonal
oscillation with two maxima in June and December and two minima in May and
September (Figure: 4).While Puranik (1990) and Vijay Kumar (2002) observed
secondary maxima during post-monsoon season and opined that this could be due
to increased incursion of distinct water mass flowing along the coast and
biological status of the environment with intense photosynthetic activity.
Chandrashekara (2004) observed one pre-monsoon peak and a major monsoon
peak followed by two small peaks in post-monsoon season in Sita-Swarna estuary,
Udupi.
The spatial variation of dissolved oxygen indicated that the stations located
at and nearer to the confluence registered larger variations between the months.
Whereas, stations located away from the confluence registered a narrow range of
variations between the months. Patil (1987), Puranik (1990) and Tripathi (2002)
observed a similar type of spatial variation in Cochin backwaters and in
Nethravati-Gurupur estuary respectively. Chandrashekar (2004) observed that the
stations located away from the bar mouth had registered relatively higher
dissolved oxygen than the stations located nearer to the bar mouth.
5.2.4. Water salinity
The perusal of the literature indicated that among various hydrographical
parameters, salinity variation in the estuary exerts a distinct influence on the
occurrence and distribution of organisms. Further, it is also known that salinity in
any estuary gets influenced by rainfall, evaporation, run off from the land drainage
and the degree of dilution of sea water by the freshwater. It is understood that the
influx of freshwater in an estuary will bring down the concentration of sodium
(Na) and chloride (Cl) ions, but bivalent ions like calcium, magnesium, potassium,
sulphate and carbonate ions increase in their concentration. Since these difference
in absolute concentration and their ratios will influence the movement of bivalent
cations between the organisms and environment affecting the osmotic property.
Therefore the selection and distribution of species in an estuary is influenced both
by total salt content and ionic concentrations.
In the present investigation, the salinity of surface water fluctuated from 0.21 to
34.49 ppt registering an annual range of 34.28 ppt between the two estuaries
(Table 6). Reddy (1982) and Patil (1987) registered an annual range of 35.90
ppt and 34.46 ppt respectively in Nethravati-Gurupur estuary. In Mandovi
estuary, Varma et al. (1975) recorded an annual range of 34.00 ppt. However,
lower annual range of 32.00 ppt was recorded by several authors in Hoogly-
Matlah estuary. Puranik (1990) recorded an annual range of 35.28 between the
two extreme values of salinity and Vijay Kumar (2002) recorded a range of
30.50 ppt in Nethravati-Gurupur estuary. From the data, (Table 6) it is evident
that both Haladi and Chakra estuary showed an Holohelinicum condition
(Kinne, 1971) during the study period.
Based on the seasonal variation of salinity, it is clear from the Figure 5,
that the estuary can be divided into three distinct salinity regimes, a higher saline
regime in pre-monsoon season, extremely lower salinity regime in monsoon
season and gradual increasing trend during post-monsoon season. The seasonal
distribution of salinity in various estuaries and brackish water was studied by
Menon et al. (1977), Bhat (1979), Reddy (1982), Patil (1987), Puranik (1990),
Tripathi (2002) and Chandrashekara (2004) along south west coast of India.
The higher saline conditions during the pre-monsoon season could be due
to low freshwater drainage and higher rate of evaporation. The extremely low
saline condition and pulsating regime during monsoon season between June and
August is obviously due to influence of freshwater during south west monsoon
season. It is interesting to note that there was sudden increase in salinity values
from less than 1.00 ppt in August to almost 22.0 to 24.0 ppt in September at
station 1, 3 and 5, which were located at and nearer to the confluence. Whereas
degrees of salinity increase is comparatively lesser at station 2 and 4 located away
from the confluence in Haladi-Chakra estuary respectively. This sudden increase
at the end of monsoon season indicates the intrusion of up welled high saline
water from the adjoining sea and coupled with reduced strength of riverine flow.
Similar observations were made by Chandrashekara (2004) in Sita-Swarna estuary
of Udupi district.
During the post-monsoon season, salinity values exhibited a pulsating
variation with peaks and troughs in every alternate months. However, it is
interesting to note that these conditions were within the brackish water conditions.
A critical look at the distribution of salinity at different stations during pre-
monsoon season indicated that the region underwent a clear mixoeuhaline
conditions (Venice classification). In June, July and August except at confluence
water the remaining stations exhibited a clear limnetic condition. However, the
study carried out by Puranik (1990), Tripathi (2002) and Chandrashekara (2004)
observed limnetic condition throughout the Nethravati-Gurupur and Sita-Swarna
estuary respectively. From September to January at all the stations exhibited a
clear mixoeuhaline condition, where salinity fluctuated between 5.0 ppt to 30.0
ppt. Thus, it can be stated that the whole estuary during the period of study
underwent three distinct types of brackish water conditions such as mixoeuhaline,
limnetic and mesohaline conditions. Such detailed classification of brackish
waters like Nethravati-Gurupur and Sita-Swarna estuary was documented by Patil
(1987), Puranik (1990) and Chandrashekara (2004) respectively.
5.3. Nutrients 5.3.1. Nitrogenous nutrients
5.3.1.1. Ammonia-nitrogen
Ammonia is one of the important nutrients often that regulates production
in aquatic environment. Generally ammonia is available in low concentrations in
natural waters and in turn gets regulated by certain important hydrographical
parameters such as pH, temperature etc. Being an intermediately compound in
nitrogen cycle its concentration is subjected to regular fluctuation during the
process of nitrification and denitrification. It is understood that ammonia is
preferred as a nitrogenous nutrient by many phytoplankton species.
In the present study, the ammonia concentration fluctuated from 0.10 µg-
at/l to 17.99 µg-at/l (Table 7) in the surface water. Nagarajaiah and Gupta (1983)
recorded from traces to 20.86 µg-at/l in the brackish water ponds of Nethravati
estuary. In the same environment, Suresh (1987) recorded values from traces to
29.17 µg-at/l. While Bhattacharjaya (1991) in Gurupur estuary recorded as high as
28.73 µg-at/l. Chandrashekara (2004) recorded the ammonia value which is
fluctuated between 0.95 and 16.51 µg-at/l in Sita-Swarna estuary.
In the present study, the ammonia value was found to be less when
compared with Nethravati-Gurupur estuary values, but was almost similar with
that of the values of Sita-Swarna estuary. This lower value could be due to lower
amount of domestic sewage discharge coupled with low quantity of offal in
Haladi-Chakra estuary. In Porto Novo waters along the east cost of India,
Ramadhas et al. (1976) recorded ammonia concentration which ranged from 0.76
to 1.5 µg-at/l in the brackish water. Raghothaman and Patil (1995) while working
in Narmada estuary, observed low levels of ammonia that ranged from 0.25 to
9.15 µg-at/l. During the present study, the seasonal fluctuation of this nutrient
gradually exhibited a trend and recorded the first peak in May at all the stations.
During monsoon season, a distinct peak was observed in July at all the stations
except at station 4 situated at Chakra estuary. There after a pulsating trend was
observed at all the stations in post-monsoon season, although the values were
lower but exhibited an almost increase in trend except in the month of December
where the concentration was very low at all the stations. From the Figure 6, it is
evident that the ammonia exhibited peaks in pre-monsoon and monsoon and
gradual stepping up trend in post-monsoon season. The pre-monsoon peak could
be attributed to intense biological activity, while the monsoon peak to the
increased freshwater drainage.
Nagarajaiah and Gupta (1983) observed monsoon and post-monsoon peaks
in the brackish water ponds of Nethravati estuary. Pradeep and Gupta (1988)
documented the peak values during June, November and April in brackish water
ponds of Mulki estuary. Tripathi (2002) documented pre and post-monsoon peaks
with varying intensity in the surface water of Nethravati-Gurupur estuary.
Whereas Chandrashekara (2004) observed trimodal seasonal oscillation in Sita
Swarna estuary. However, in the present study only two peaks were observed
which coincided with the pre-monsoon and post-monsoon season.
5.3.1.2. Nitrite- nitrogen
Among the three forms of nitrogenous nutrients, nitrite is considered to be
a very unstable form being an intermediately stage in nitrogen cycle. Nitrite gets
converted into a nitrate by nitrification or changes to ammonia or ammonium form
by denitrificaton process. In the natural waters, nitrite is generally available in
trace quantity.
In the present study, nitrite concentration varied from 0.20 to 4.23 µg-at/l
in the surface waters (Table 8). De’Souza (1977) while working on the monitoring
of some environmental parameters reported the values ranging from traces to
8.33µg-at/l at Zuari estuary. Sahu (1981) in Nethravati Gurupur estuary
documented the values varied from 0.02 to 2.01 µg-at/l. Nagarajaiah and Gupta
(1983), Suresh (1987), Pradeep and Gupta (1988), Sudhir (1990), Bhattacharjaya
(1991), Mathew (1994), Tripathi (2002) and Chandrashekara (2004) recorded
value ranged from 0.87 to 2.02, 0.35 to 8.72, traces to 23.15, 0.04 to 7.84, 0.04 to
5.85, traces to 3.5, 0.23 to 4.64 and 0.02 to 5.83 µg-at/l respectively, in the various
brackish water of Dakshina Kannada and Udupi districts. In Porto Novo waters of
east coast of India, Ramadhas et al. (1976) reported the nitrite values ranged from
0.64 to 2.61 µg-at/l in backwaters and estuarine regions. Santhanam et al. (1994)
recorded the range from 0.5 to 698.0 µg-at/l in Narmada estuary, east coast of
India. The present value is in agreement with the values recorded by Tripathi
(2002) in Nethravati-Gurupur estuary. In present study, the seasonal distribution
of this nutrient exhibited higher values in February at all the stations and there
after with a dip in the month of March. The values progressively increased and
reached a peak in July/September in almost all stations. In the post-monsoon
season with lower values in October and the nitrite concentration progressively
increased and reached to another peak in January. Therefore from the Figure 7, it
is evident that nitrite by and large exhibited trimodal seasonal oscillation.
Nagarajaiah (1980) recorded a primary peak in March in a semi-enclosed
brackish water pond of Nethravati estuary. Pradeep and Gupta (1988) recorded a
distinct primary peak during July in brackish water pond of Mulki estuary. Sudhir
(1990) documented a trimodal seasonal oscillation in the Nethravati-Gurupur
estuary. While Mathew (1994) documented a primary peak during January and
secondary peak in September in a semi-enclosed brackish water pond of
Nethravati estuary. Recently, Tripathi (2002) and Chandrashekara (2004)
observed trimodal oscillation of this nutrient in Nethravati-Gurupur and Sita-
Swarna estuary respectively. This spatial distribution of this nutrient revealed
lower values at stations located at and near to the confluence when compared to
those located away from it.
5.3.1.3. Nitrate-nitrogen
Nitrate is the end product of nitrification and is the most stable nitrogenous
nutrient. In recent years more attention has been given to nitrogenous nutrient
which is considered to be most potential limiting nutrient in the aquatic
environment in general and being particular in brackish water and estuarine water.
Goldman (1976) pointed out that in coastal phytoplankton species ratio of
nitrogen to phosphorus by atom is between 10:1 to 20:1. While in water it is only
5:1 therefore, enrichment of water with nitrogen enhanced algal growth which
proves that the nitrogen exerts its influence on primary productivity more than that
of other nutrients.
The present study showed nitrate concentration varied from 1.40 to 20.97
µg-at/l (Table 9). In Nethravati-Gurupur estuary, Sahu (1981) reported a values
ranging from 0.02 to 0.87 µg-at/l. Suresh (1987), Sudhir (1990), Vedamurthy
(1992), Mathew (1994), Gowda et al. (2001a), Tripathi (2002) and
Chandrashekara (2004) documented the values ranging from traces to 9.86, 0.10
to 6.85, 0.04 to 5.58, 0.02 to 3.08, traces to 7.28, 0.94 to 79.84 and 0.43 to 65.95
µg-at/l in Nethravati-Gurupur and Sita-Swarna estuary respectively.
Devassy (1983) and Devassy and Goes (1989) observed nitrate values,
which fluctuated from 0.23 to 0.92 µg-at/l. and traces to 3.76 µg-at/l in the
estuarine environments of Goa. In the same environment, Verlencar (1987) and
De’Souza (1999) recorded the values ranging from traces to 2.4 µ mol/l and traces
to 3.3 µ mol/l respectively. Krishna Kumari et al. (2002) in Mandovi estuary
recorded the values between 1.17 to 5.67 µ mol/l.
Along the east coast of India, Kannan and Krishnamurthy (1985) in the
Porto Novo aquatic biotope have recorded nitrate values ranging from 4.75 to
30.50 µg-at/l. Santhanam et al. (1994) in the Tuticorin Bay recorded values as
low as 0.2 to 0.7 µg-at/l. Gouda and Panigrahy (1995) in Rushikulya estuary
observed the nitrate values, which ranged from 0.37 to 18.4 µg-at/l. While
Ragothaman and Patil (1995) in Narmada estuary, documented the nitrate values
ranged from 0.5 to 775.00 mu. g/l.
The value recorded in Haladi-Chakra estuary is in agreement with the
values recorded by many authors worked along the west coast of India. It is
evident from the Figure 8, that the first peak was recoded in April/May at all the
stations. The second peak values were observed during monsoon season. The third
high values were observed in January at all the stations. Therefore, it is clear from
the data that this nutrient exhibited by and large trimodal seasonal oscillation.
The higher peak of nitrate during monsoon season was recorded by Gupta
et al. (1980) in Nethravati-Gurupur estuary. Nagarajaiah and Gupta (1983)
recorded the bimodal pattern of seasonal distribution with primary peak in June
and secondary peak in April in the brackish water ponds of Nethravati estuary.
Pradeep and Gupta (1988) observed two peaks one in June/July and the other in
December in the brackish water ponds of Mulki estuary. Suresh (1987) observed
the dominant peak in June, smaller peaks during September/December and April
in Nethravati-Gurupur estuary. Sudhir (1990) documented three peaks, one in
March/April, other during June/July and the third in November/December.
Mathew (1994) recorded two major peaks in June/July, October and smaller peaks
in March/April in the same estuary. Tripathi (2002) recorded a primary peak in
April and two smaller peaks in post-monsoon season in Nethravati-Gurupur
estuary. Recently Chandrashekara (2004) observed a primary peak in June/July
and two peaks in post-monsoon season with maximum peak in October month in
Sita-Swarna estuary.
In the present study, although triple oscillation of seasonal variation was
observed at all the stations the primary and secondary peaks varied from one
station to the other. A primary peak of pre-monsoon season was observed at
station 1, 3 and 4. Whereas, the primary peak at station 2 and 5 was observed in
monsoon season.
5.3.2. Phosphate-phosphorous
Dissolved phosphate occurs mainly has inorganic ortho phosphate. This is
one of the major nutrients for primary production in the aquatic environment.
Often phosphate is identified as the nutrient responsible for eutrophication in
confined water. In the present study, the concentration of phosphate in the surface
water ranged from 0.24 to 9.34 µg-at/l (Table 10). In the Nethravati-Gurupur
estuary, Reddy (1982), Suresh (1987), Vedamurthy (1992), Mathew (1994),
Gowda et al. (2001b) and Tripathi (2002) reported values as high as 2.97, 3.50,
2.35, 4.82, 4.32 and 6.31 g-at/l respectively. Chandrashekara (2004) has
recorded phosphate-phosphorous concentration ranging from 0.15 to 9.10 g-at/l
in the Sita-Swarna estuary of west coast of India.
Verlencar (1987) recorded values as high as 2.4 g-at/l, along the estuarine
waters of Goa. The lower phosphate value of 0.11 to 0.56 µ mol/l in Mandovi
estuary was recorded during pre-monsoon season by De’Souza (1999) and the
author has attributed this low concentration to discharge of mining rejects.
Krishna Kumari et al. (2002) recorded phosphate values as high as 8.06 µ mol/l in
Mandovi-Zuari estuary.
Along the east coast, Gouda and Panigrahy (1995) in Rushikulya estuary
documented the values of phosphate in surface water, which range from 0.09 to
1.86 g-at/l. The phosphate concentration in the surface waters of Haladi-Chakra
estuary was found to be slightly higher than that of the values recorded by many
authors in Nethravati-Gurupur estuary, Mulki estuary and Mandovi-Zuari
estuarine complex respectively. However, the present higher value is almost
similar to the higher values obtained by Krishna Kumari et al. (2002) in Mandovi-
Zuari estuary and Chandrashekara (2004) in the Sita-Swarna estuary.
From the Figure 9, it is revealed that the surface water phosphate
concentration exhibited first peak in February at all the stations. The monsoon
primary peak was observed in July at all the stations. During post-monsoon season
phosphate values gradually decreased and reached to a minimum in January. Thus
it can be stated that this nutrient exhibited bimodal seasonal oscillation. However,
Nair et al. (1975) reported the primary peak during late pre-monsoon and early
monsoon and smaller peaks during September and October in Cochin backwaters.
However, Devassy and Goes (1989) recorded the peak phosphate concentration in
October in Mandovi-Zuari estuary of Goa. The present observation is in
agreement with the works of Suresh (1987), Sudhir (1990), Gowda et al. (2001b)
and Tripathi (2002) reported bimodal seasonal oscillation in Nethravati-Gurupur
estuary. However, Chandrashekara (2004) observed higher values of phosphate
concentration but could not get clear-cut seasonal oscillation. The spatial
distribution of this nutrient has revealed higher values at stations situated away
from the confluence region.
5.3.3. Silicate-silicon
Silicate a terregenous nutrient that is generally available in higher
quantities in estuarine environment. In comparison to other nutrients, it is always
present in higher quantity than the absolute requirement of phytoplankton.
However, the silicate might become a limiting factor immediately after the diatom
blooms.
In the present study, silicate in the surface water varied from 0.19 to 91.14
g-at/l (Table 11). In Mulki estuary, Reddy et al. (1985) recorded peak silicate
value of 37.08 g-at/l. While Suresh (1987) and Vedamurthy (1992) in
Nethravati-Gurupur estuary recorded values as high as 134.99 and 157.82 g-at/l
respectively. Teleng et al. (1983) documented the values as high as 57.4 g-at/l in
Kanasgeri backwater along the east coast of India. In the backwater and estuarine
environment of Porto Novo, Ramadhas et al. (1976) recorded a peak value of 71.0
g-at/l and 86.0 g-at/l respectively. Ragothaman and Patil (1995) observed
silicate values in Narmada estuary, which varied from 0.04 to 1.7 g-at/l. Mathew
(1994) recorded 126.0 g-at/l in brackish water ponds of Nethravati estuary. In
the Mandovi estuary, Goa, De’Souza (1999) observed silicate values ranging from
1.25 to 130 µ mol/l .Tripathi (2002) documented silicate concentration, which
varied from 3.84 to 136.44 g-at/l in Nethravati-Gurupur estuary. Chandrashekara
(2004) while working in Sita-Swarna estuary documented the silicate
concentration varying from 0.85 to 136.44 g-at/l. In the present study, the silicate
concentration is lesser than that of the authors worked in various estuaries of west
coast of India. However, the present values were almost nearer to the values
recorded by Ramdhas et al. (1976), Teleng et al. (1983), and Ragothaman and
Patil (1995).
It is evident from the Figure 10, that the silicate concentration exhibited
peaks and trough at every alternate month throughout the period of study.
Therefore, it can be stated that this nutrient did not exhibit any clear cut seasonal
variation. Suresh (1987), Sudhir (1990), Vedhamurthy (1992), De’Souza (1999),
Krishna Kumari et al. (2002) and Chandrashekara (2004) have recorded bimodal
seasonal oscillation in Nethravati-Gurupur, Mandovi-Zuari and Sita Swarna
estuarine complex respectively. From the data, it is evident that the stations
located at and near confluence registered comparatively higher concentration of
silicate than that of the station located away from it.
5.4. Phytoplankton pigments
The micro and macro algae synthesize organic matter through the process
of photosynthesis. In this process, conversion of radiant energy into chemical
energy is intimately dependent upon chlorophyll pigments, which are embedded
in thalakoids of each chromatophore. In great majority of algae accessory
pigments such as caroteins, xanthophylls and phycobilins play a major role in
transferring required wavelength of light to chlorophyll. Many investigators
related chlorophyll of phytoplankton to total organic matter synthesized at any
given time {(Riley et al. (1949) and Ryther (1956)}. It is well known that
chlorophyll contains fat-soluble compounds in the pigment with magnesium at the
center (Yentsch and Scagel 1958). A pigment without magnesium looses the
phyto linkage from the chlorophyll resulting in the formation of phaeophytin. The
caroteins are one of the accessory plant pigments with long hydrocarbon chain
ending in the ring structure (Raymont, 1980). Among the three chlorophyll
pigments (a, b, c) the estimation of active chlorophyll-a directly provides the total
standing crop of any aquatic environment.
5.4.1. Chlorophyll-a
In the present investigation, chlorophyll-a concentration varied from 0.54
to 50.21 mg/m3 (Table 12). Bhattathiri (1976) observed chlorophyll values ranging
from 2.2 to 12.6 mg/m3 in the estuarine waters of Goa. Verlencar (1984) in
Mandovi estuary documented chlorophyll values as high as 11.3 mg/m3. While
Desai et al. (1984) in different estuaries of Gujarat documented chlorophyll-a
values as high as 33.45 mg/m3. In Cochin estuary, Sivadasan and Joseph (1995)
observed chlorophyll-a as high as 70.35 mg/m3. In polluted Bombay harbour
Thana-Bassein creek estuarine complex, Ramaiah and Nair (1998) recorded 3.5
mg/m3of chlorophyll-a. In lower reaches of Vashista estuary, Vijayalakshmi et al.
(1998) documented 3.1 mg/m3 of chlorophyll-a. Krishna Kumari et al. (2002) in
Mandovi-Zuari estuary, observed the chlorophyll-a content which ranged from
0.01 to 4.33 mg/m3. Selvaraj et al. (2003) observed chlorophyll-a values, which
varying from 0.93 to 8.85 mg/m3 in Cochin backwaters.
In Nethravati-Gurupur estuary, Suresh (1987) observed chlorophyll-a
values ranging from trace to 24.63 mg/m3. Mathew (1994) documented values
ranging from 0.12 to 33.1 mg/m3. However, Manjappa (1987) documented
chlorophyll-a value as high as 24.56 mg/m3. In Nethravati-Gurupur estuary,
Gowda et al. (2001b) observed chlorophyll-a values varied between 1.18 and
11.35 mg/m3. Whereas Gupta et al. (2002) recorded value as high as 17.62 mg/m3
in Hangarkatte estuary. Tripathi (2002) observed chlorophyll-a content, which
varied between 0.53 and 20.29 mg/m3. Chandrashekara (2004) while working in
the distribution of phytoplankton in Sita-Swarna estuary observed chlorophyll-a
value in the range of 0.65 to 14.01 mg/l. In the present investigation, the values of
chlorophyll-a are slightly higher than that of the values recorded by earlier
authors.
In Narmada estuary, Gaibhiye et al. (1981) documented chlorophyll values
ranging from 7.8 to 31. 84 mg/m3. In Vellar estuary, Kawabata et al. (1993)
observed chlorophyll-a ranging from 3.6 to 6.5 mg/m3. Santhanam et al. (1994)
while working on the impact of Trichodesmium bloom on the phytoplankton and
productivity, in Tuticorin Bay recorded chlorophyll-a value as high as 535.26
mg/m3.
In the present investigation, higher chlorophyll-a values were observed in
the month of March at all the stations. The second maxima were recorded in
July/August at all the stations. While the post-monsoon peak was observed in
October/November at all the stations. Therefore from the Figure 11, it is evident
that the chlorophyll-a in this region exhibited trimodal seasonal oscillation. The
post-monsoon season was higher than that of monsoon at all stations except at
station 2 where monsoon peak was higher.
In the Cochin backwater, Joseph and Pillai (1975) recorded highest
chlorophyll-a value during post-monsoon season and moderate during monsoon
season. Whereas Gopinathan et al. (1994) observed a single dominant peak during
monsoon in the same environment. Devassy and Goes (1989) observed a
dominant post-monsoon peak in Camburjua and Zuari system of Goa. Suresh
(1987) documented two peak values of chlorophyll-a in June/July and December
in Nethravati estuary. Manjappa (1987) in the coastal waters of Mangalore
recorded dominant peak in pre-monsoon season and smaller peak during post-
monsoon season. Nair (1990) observed a peak value of chlorophyll-a during April
in Edaiyur Sandras estuarine systems at Kalpakam. Mathew (1994) in brackish
water ponds of Nethravati estuary recorded peak value of chlorophyll-a during
monsoon and post-monsoon season.
Gowda et al. (2001b) documented pre and post-monsoon peaks of
chlorophyll-a in Nethravati estuary. Tripathi (2002) observed pre and post-
monsoon peaks of chlorophyll-a in Netharavati-Gurupur estuary. The post-
monsoon peak was more dominant than that of pre-monsoon peak.
Chandrashekara (2004) observed dominant peak in post-monsoon season. In the
present study, the seasonal variation of chlorophyll-a is in agreement with a
variation recorded by Joseph and Pillai (1975), Devassy and Goes (1989),
Manjappa (1987) and Tripathi (2002).
While comparing chlorophyll-a with that of salinity variation it is evident
that the period of high chlorophyll-a content coincided with the period when
mixoeuhaline conditions of water existed in the estuary.
5.4.2. Phaeophytin Appreciable quantities of phaeophytin pigments, a degraded product of
chlorophyll in the present study fluctuated between 0.92 to 61.74 mg/m3 (Table
13). The information on the variation of phaeopigments in space and time in
brackish water environment along both the coast of India is scanty. Sundararaj and
Krishnamurthy (1975) have reported the distribution of phaeopigments in
backwaters and reported increase in phaeopigment levels corresponding to
increase of chlorophyll-a.
In Edaiyur Sandras estuarine system, Nair (1990) observed the same
pattern of relationship between chlorophyll and phaeopigments. Suresh (1987)
and Manjappa (1987) while working in the Nethravati estuary and coastal waters
off Mangalore, have not observed a clear relationship between chlorophyll-a and
phaeopigments in their seasonal variation. Mathew (1994) while working in semi-
enclosed pond of Nethravati estuary observed monsoon, post-monsoon and pre-
monsoon peaks and peak values were as high as 224.28 mg/m3. However, Nayar
and Gowda (1999) documented phaeopigment values to range from 3.02 to 30.52
mg/m3 in Talapady lagoon. Gowda et al. (2001b) recorded phaeopigment values,
which varying between 0.11 and 32.04 mg/m3 in Nethravati estuary. Gupta et al.
(2002) recorded a high value of 24.83 mg/m3in Nethravati estuary, 30.44 mg/m3 in
Pavanje estuary and 28.04 mg/ m3 in Kollur estuary of Dakshina Kannada and
Udupi District.Tripathi (2002) recorded the value as high as 36.56 mg/m3 in
Nethravati-Gurupur estuary. Chandrashekara (2004) observed the values as high
as 27.78 mg/m3 in Sita-Swarna estuary.
In the present study, the seasonal variation of this parameter indicated that
distinct three peaks one during pre-monsoon, the second in monsoon and the last
peak in post-monsoon season. Therefore from the Figure 12, it can be stated that
phaeopigments exhibited trimodal seasonal oscillation. Among the three peaks
post-monsoon peak was predominant at all the stations except at station 2, where
it was in monsoon season. The present values are in agreement with the values
recorded by Mathew (1994) observed monsoon, post-monsoon and pre-monsoon
peaks. However, Tripathi (2002) and Chandrashekara (2004) did not observe
clear cut seasonal variation although they establish a close relationship between
chlorophyll-a and phaeophytin pigments.
5.5. Sediment analysis 5.5.1. Sediment temperature
Sediment temperature is known to influence the chemical characteristics of
interstitial waters, there by determining the occurrence, abundance and
distribution of benthic organisms. Therefore, the sediment temperature in the
present study was recorded as a related parameter of macrobenthos. During the
study period the sediment temperature fluctuated from minimum of 25.5oC to a
maximum of 32.9oC (Table 14).
The minimum and maximum sediment temperature was slightly more than
that of surface water temperature. This kind of sediment temperature distribution
along the Mangalore coast was observed by Reddy (1983), Sahoo (1985), Prabhu
(1992) and Mohan Kumar (1999). Varshney et al. (1983) documented increased
sediment temperature from inshore to offshore region along the coastal waters of
Versova, Bombay. Similarly, increased sediment temperature was observed by
Shanthanagouda (2001) in Nethravati-Gurupur estuary, Nagendra Babu (2004) in
Sita-Swarna estuary and Shiva Kumar (2005) in Mulki-Pavanje estuary
respectively along south west cost of India.
The seasonal distribution of sediment temperature revealed a gradual
decrease in the values during south west monsoon season. In post-monsoon
season, the temperature showing peak in October. While in pre-monsoon season,
it exhibited an increasing trend with peak in May. Thus it is clear from the Figure
13, the sediment temperature in Haladi-Chakra estuarine complex exhibited by
and large bimodal seasonal oscillation. Bhat (1979) and Shanthanagouda (2001)
recorded unimodal seasonal oscillation of sediment temperature in Nethravati-
Gurupur estuary. Whereas Nagendra Babu (2004) observed bimodal seasonal
oscillation with a primary peak in April during pre-monsoon season and
secondary peak in October/November during post-monsoon season. Shiva Kumar
(2005) recorded a trimodal seasonal oscillation of sediment temperature in Mulki-
Pavanje estuary.
The spatial distribution of sediment temperature revealed slightly higher
values at station 1 (confluence) compared to other stations, which are situated in
Haladi-Chakra estuary. However, Shanthanagouda (2001), Nagendra Babu (2004)
and Shiva Kumar (2005) observed greater spatial variation in Nethravati-Gurupur,
Sita-Swarna estuary and Mulki-Pavanje estuary respectively.
5.5.2. Sediment pH
It is well known that pH is single parameter in the interstitial habitat that
can change the form of many chemical parameters, which influence the benthic
organisms. During the present study, sediment pH varied from a lowest of 6.18 to
a highest of 9.19 (Table 15). Jayaraj (1982) and Reddy (1983) while working on
the benthos of South Canara coast documented slightly higher range of pH which
fluctuated from 7.60 to 8.00. Whereas Sahoo (1985) recorded a low of 6.05 and
high of 8.45. Shanthanagouda (2001) documented the sediment pH which ranged
from 6.80 to 8.00 in Nethravati-Gurupur estuary. However, Rajesh et al. (2004)
recorded the mean value of the sediment pH, where values ranged from 5.43 to
6.06 in brackish water impoundments along Nethravati estuary, Dakshina
Kannada. Nagendra Babu (2004) observed the sediment pH, which fluctuated
from 6.70 to 7.90 in Sita-Swarna estuary Udupi. Shiva Kumar (2005) recorded the
sediment pH of 5.6 to 8.26 in Mulki-Pavanje estuarine complex, Dakshina
Kannada. Varshney et al. (1983) documented gradual increase of sediment pH
from inshore to offshore regions in the coastal waters of Versova, Bombay.
Nasnolkar et al. (1996) documented sediment pH in Mandovi-Zuari estuary, Goa,
which ranged from 7.13 to 7.79. Along the east coast of India, Chandran et al.
(1982) recorded mud pH, which ranged from 6.74 to 8.10 in Vellar estuary. The
sediment pH recorded in the present study is in agreement with the studies carried
out in estuaries and bays along both the coast of India except with the
observations of Rajesh et al. (2004).
The seasonal distribution of sediment pH revealed higher values in the pre-
monsoon and post-monsoon season compared to lower values during the monsoon
season. This indicated that the increased freshwater flow during monsoon could
have been the possible factor to bring down pH values to almost slight acidic
condition. Whereas during the non-monsoon season the building up of the salinity
due to increased incursion of saline water could be the causative factor for
maintaining alkaline condition during post and pre-monsoon season. Therefore
from the Figure 14, it could be stated that the sediment pH exhibited lower values
in monsoon and higher values in post and pre-monsoon season.
Reddy (1983) and Sahoo (1985) observed a unimodal seasonal fluctuation
in the Nethravati-Gurupur estuary and Talapadi lagoon respectively. Nasnolkar et
al. (1996) observed slightly alkaline condition of sediment during monsoon and
post-monsoon season in Mandovi estuary, Goa. Mohan Kumar (1999)
documented unimodal seasonal oscillation in the coastal waters off Chitrapur,
Dakshina Kannada. However, Shanthanagouda (2001) observed bimodal seasonal
oscillation in Nethravati-Gurupur estuary. Nagendra Babu (2004) observed
unimodal seasonal oscillation in Sita-Swarna estuary, Udupi. Shiva Kumar (2005)
observed no distinct seasonal clear-cut peaks of sediment pH in Mulki-Pavenje
estuarine complex, Dakshina Kannada.
The spatial variation in the sediment pH during the present study indicated
by and large the uniform variation at all the stations. The higher values are
recorded at confluence (station 1) and lower values at Haladi estuary (station 2
and 3) and moderate values in Chakra estuary (station 4 and 5). The lower values
recorded in monsoon season.
5.5.3. Sediment texture
From the perusal of the literature, it is evident that textural characteristics
of sediment are the important parameters, which influence the quality and quantity
of benthos. Moreover, with meiofaunal species being smaller in size might be
expected to be more sensitive to changes in textural characteristics of the sediment
(Parsons et al. 1977). Further, the type of sediment will also determine
concentration of nutrients.
During the present investigation, the sand fraction dominated at all the
stations in all the months except in December at station 3 in Haladi estuary with
only 42.70% contribution of sand, followed by silt and the clay and it varied in
space and time (Table 16). However, silt fraction was found to be dominating at
almost all the stations during monsoon season. However, in pre-monsoon and
post-monsoon season the clay percentage was found to be lesser than silt
percentage and sand percentage. Since the sediment texture in the environment
depends on the topography of the location, the strength of riverine and tidal flow.
The composition of sediment indicated that the sediment of Haladi-Chakra
estuarine complex is greatly dominated by Sand > Silt > Clay. This could be due
to the lesser riverine strength, which is responsible for clay settlement and more
the tidal strength from seaward tide is more that could be the reason for the greater
percentage of sand in all most all the stations.
Ansari et al. (1986) while investigating on macrobenthos of central west
coast of India observed higher percentage of sand with little or no clay in the
Malpe Bay and Mangalore coast. Reddy (1983) reported dominance of sand
followed by silt and clay in Nethravati-Gurupur estuary. Ramachandra et al.
(1984) documented the greater dominance of sand and equal contribution of silt
and clay in the sediments of Mulki estuary. Seralathan (1993) in the Cochin
harbour observed higher percentage of sand, but silt and clay had equal
dominance in the sediment. Nair et al. (1993) while studying the sediment
characteristics of Cochin estuary stated that sediment texture in the estuary gets
influenced by the monsoon and mixing process in the environment. Prabhu et al.
(1993) observed dominance of sand, which gradually changes to clayey silt as the
distance, increased from the shore along the coast of Gangoli, Dakshina Kannada.
Varying characteristics of sand, silt and clay of sediments of Marmagoa harbour,
Goa were documented by Ansari et al. (1994).
Nasnolkar et al. (1996) although observed dominance of sand in the
sediment during monsoon and post-monsoon season they have documented higher
percentage of silt and clay at some stations during monsoon and post-monsoon
season in Mandovi estuary, Goa. Badarudeen et al. (1998) observed highest
percentage of sand in the sediment of Kannur mangrove region south west coast
of India. Prabhu et al. (1997) observed clayey nature of sediment of Honnavara,
North Karnataka district. Shanthanagouda (2001) while working in Nethravati-
Gurupur estuary documented sediment texture, which varied between stations and
seasons.
Mohan (2000) while working on sediment transport mechanism in Vellar
estuary observed predominance of sand at the head of the estuary with silt and
clay as subordinate constituents. Greater percentage of sand followed by silt and
clay was observed by Kailasam and Siva Kami (2004) in the sediment collected
from Tuticorin Bay, east coast of India. Nagendra Babu (2004) observed the sand
faction dominated at all the stations in all the months followed by silt and clay.
Shiva Kumar (2005) reported higher percentage of sand followed by clay and silt
in Mulki-Pavenje estuarine complex.
The present data on sediment texture, while comparing with that of the
other study, it becomes evident that every estuary exhibit different types of
sediment texture in different seasons. This is because the texture of the sediment
not only depends on season, proximity to the sea, magnitude of mixing and
activity at the adjoining coasts but also on terrigenous and anthrapogenic input.
From the data gathered on sediment characteristics and benthic population, it
becomes clear that the contribution of silt to the total sand fractions throughout the
study period at station 4 could be the favorable environment for supporting higher
density of benthic organisms.
5.5.4. Sediment organic carbon
Organic carbon in sediment is basically derived from within the ecosystem
and also by transportation of leaf and eroded materials (Likens, 1972). Sediments
rich in organic content with an active microbial flora form an important food
source for a majority of benthic organisms. Further, it is well known that sediment
texture will determine the total organic matter and inturn influence the abundance
and occurrence of benthic organisms.
Organic carbon in the sediment during the study period varied from 0.03 to
1.67% (Table 17). Ramachandra (1981) documented organic carbon in Mulki
estuary, which varied from 0.01 to 1.65 %. Similar range of organic carbon was
recorded by Bhat (1979), Reddy (1983) and Shanthanagouda (2001) in
Nethravati-Gurupur estuary, Nair et al. (1983) in Ashtamudi estuary and
Alagarsamy (1991) in Mandovi estuary, Goa. However, Nasnolkar (1996)
recorded sediment organic carbon as high as 32.77 mg C/g in Mandovi estuary,
Goa. Bijoy Nandan and Azis (1996) documented 137.09 mg C/g in the retting
areas of Kadinamkulam estuary.
Total organic carbon of sediment of Beypoor estuary (south west coast of
India) was observed by Nair and Ramachandran (2002) that varied from 0.10 to
6.54%. Along the east coast Chandran et al. (1982) documented sediment organic
carbon as high as 14.88 mg C/g in Vellar estuary. While Sasamal et al. (1986)
documented sediment organic carbon percentage, which varied between 0.59 and
4.12%. However, Prabha Devi (1994) observed as high as 27.8 mg C/g in
Coleroon estuary during post-monsoon season. Kumary et al. (2001) documented
sediment organic carbon, which varied between 2.4 and 83.3 mg C/g in Poonthura
estuary.
The seasonal variation of organic carbon revealed primary peak in March
and it reaches maximum of 1.67% in July with very low values in April of 0.03%.
The values gradually increased and reached the peak in July during monsoon
season and further the values exhibited slight increase up to 1.5% during post-
monsoon season of October. Therefore from the Figure 18, it becomes evident that
the sediment organic carbon in this estuary exhibited a trimodal seasonal
oscillation with one pre-dominant peak in monsoon and two smaller peaks in pre
and post-monsoon season. Nasnolkar et al. (1996) while working in Mandovi
estuary, Goa, observed peak values of sediment organic carbon from July to
September during monsoon season. However, in Nethravati-Gurupur estuary
higher values during April/November/December was observed by
Shanthanagouda (2001). Nagendra Babu (2004) observed the organic carbon in
the range of 0.01% to 1.84% exhibited a trimodal seasonal oscillation with one
pre-dominant peak in monsoon season and two smaller peaks in pre and post-
monsoon season. Shiva Kumar (2005) reported the organic carbon in the range of
0.06% to 1.05% in Mulki- Pavenje estuarine complex, Dakshina Kannada.
The spatial distribution of organic carbon during the study revealed
comparatively higher percentage at station 5 and station 4 in Chakra estuary than
that of station 1 at confluence and station 3 and station 2 located in Haladi estuary.
From the data gathered, it becomes clear that at all the stations during the
period of study the organic carbon was well bellow 3%. Therefore, it could be
stated that this estuarine sediment does not fall under the category of polluted
environment. This perhaps is due to existence of vigorous oxidation activity in the
sediment.
5.6. Phytoplankton 5.6.1. Qualitative distribution
In the present investigation the total number of phytoplankton cells varied
from 14524 to 20355607 cells/m3 (Table 18 to 22).
Perumal et al. (1999) observed high populatation density of phytoplankton
to the extent of 1,99,600 cells/l in Vellar estuary. Tripathi (2002) observed more
than 1,19,00,000 cells/m3 in Nethravati-Gurupur estuary. In Cochin backwaters,
Selvaraj (2003) documented 2,35,000 cells/l. Whereas Chandrashekara (2004) has
documented more than 1,16,00,000 cells/m3 in Sita-Swarna estuary. However in
the present investigation, the total number of phytoplankton cells accounted was
2,03,55,607 cells/m3, which were almost similar to that of the values recorded by
Perumal et al. (1999) and Selvaraj (2003).
The peak abundance of phytoplankton was observed both in pre-monsoon
season and post-monsoon season with a small rise at the end of pre-monsoon and
monsoon season. However, during monsoon and early post-monsoon the number
of cells were minimum. From the Figure 19, it is evident that the total
phytoplankton cells exhibited by and large bimodal seasonal oscillation. However,
Tripathi (2002) and Chandrashekara (2004) observed multimodal seasonal
oscillation in Nethravati-Gurupur and Sita-Swarna estuary respectively.
5.6.1.1. Cyanophyceae
Investigations on the occurrence and distribution of blue green algae have
been carried out by many scientists. Many of the species of blue green algae are
known to fix atmospheric nitrogen and exert influence on nutrient budget of the
water body. Trichodesmium sp., Oscillatoria sp. and Lyngbya sp. are the dominant
forms of cyanophycea in marine and estuarine environment. Instances of
discoloured water phenomenon due to Trichodesmium sp. in Indian waters have
been studied by Bhimachar and George (1950), Prabhu et al. (1965) and Devassy
et al. (1978) Ramesha et al. (1992) and Ronald (2001).
In the present investigation, the Cyanophyceae consisted of various species
belonging to the genera Anabaena, Lyngbya, Merismopedia, Microcystis, Nostoc,
Osillatoria, Spirulina and Trichodesmium. Among blue green algae
Trichodesmium, Osillatoria and Merismopedia occurred frequently with greater
numbers, whereas other forms occurred less frequently with low numbers.
Kumar (1984) while working on the seasonal distribution on the plankton
in the coastal waters of Mangalore documented only one species of blue green
algae, namely Trichodesmium erythraeum with the greater abundance. Further, the
author documented its greater influence on the total biomass of phytoplankton.
Pradeep (1980) observed the dominance of Merismopedia in brackish water ponds
of Mulki estuary, Dakshina Kannada. Mathew and Nair (1980) observed the
dominance of Cyanophyceae in Ashtamudi estuary, Kerala. Reddy (1982)
recorded Anabaena, Pharmidium, Microcystis and Oscillatoria in the water of
Mulki estuary. Whereas Perumal et al. (1999) observed the dominance of
Trichodesmium erytherium in Vellar estuary. Tripathi (2002) and Chandrashekara
(2004) observed the dominance of Trichodesmium, Oscillatoria and
Merismopedia in Nethravati-Gurupur estuary and Sita-Swarna estuary of
Dakshina Kannada and Udupi districts respectively.
In the present study, the blue green algae consisted of Oscillatoria,
Trichodesmium and Merismopedia which were abundant during pre-monsoon
season at all the stations except at station 3 (Table 18 to 22 and Figure: 20 to 22).
During monsoon season, stations located at and near the confluence recorded
moderate numbers of Oscillatoria, Trichodesmium and Merismopedia. In addition
to these Nostoc, Spirulina were present in low numbers. During post-monsoon
season, Oscillatoria along with Merismopedia formed the bulk of the blue green
algae. From the data collected, it becomes clear that the greater abundance of blue
green algae was observed only when salinity was higher during pre and post-
monsoon season. During low saline regime the species of Spirulina and Lyngbya
were found along with oscillatoria in low numbers.
Kumar (1984) observed the presence of Trichodesmium sp. almost
throughout the year in coastal water of Mangalore. Devassy and Goes (1988)
observed the abundance of Trichodesmium during pre and post-monsoon season in
Mandovi-Zuari estuarine complex. While Puranik (1990) documented higher
abundance of Trichodesmium during later half of pre-monsoon season in
Nethravati-Gurupur estuary, Mangalore. In the same area, Ronald (2001)
documented the greater abundance of Trichodesmium during post-monsoon
season and Gupta et al. (2002) recorded the dominance of Trichodesmium only
during the pre-monsoon in the same environment. Eswari and Ramani Bai (2002)
observed the dominance of Trichodesmium and Oscillatoria during non-monsoon
months in Adyar estuary. Tripathi (2002) observed the abundance of
Trichodesmium when the salinity was high and the presence of Lyngbya and
Merismopedia when salinity was low in Nethravati-Gurupur estuary. The
dominance of Microcystis, Nostoc and spirulina during the monsoon months and
the pre-ponderance of Trichodesmium and Oscillatoria were observed by
Chandrashekara (2004) in Sita-Swarna estuary.
In the present study, the occurrence and seasonal distribution of blue green
algae was found to be similar to that of the observation made by Pradeep and
Gupta (1988) in brackish water ponds of Mulki estuary and Chandrashekara
(2004) in Sita-Swarna estuary.
5.6.1.2. Chlorophyceae In the present investigation, several species of green algae belonging to 16
genera were recorded. Among them the Ulothrix, Mougeotia, Closterium,
Pediastrum, Staurastrum, Sphaerocystis, Dinobryon and Zygnema occurred more
frequently with fairly good numbers (Table 18 to 22).
Mathew and Nair (1980) recorded the abundance of Spirogyra, Desmidium
and Pediastrum during monsoon and early post-monsoon season in Ashtamudi
estuary, Kerala. Reddy (1982) documented presence of Mougeotia, Pediastrum
and Spirogyra during the early part of monsoon season in Mulki estuary,
Dakshina Kannada. However, Patil (1987) documented the presence of
Agmerellum during pre-monsoon season and Pediastrum during post-monsoon
season in Nethravati-Gurupur estuary. Joseph and Pillai (1975) and Patnaik and
Sarkar (1976) have observed higher number of green algae during the monsoon
season in different estuaries of India. Puranik (1990) has recorded the dominance
of Spirogyra, Pediastrum, Eudorina and Volvax during monsoon season in
Nethravati estuary, Dakshina Kannada. Gowda et al. (2001c) observed the
dominance of Spirogyra, Ulothrix, Zygnema and Mougeotia during monsoon and
early part of post-monsoon season in Nethravati and Gurupur estuary. Eswari and
Ramani Bai (2002) documented 8 species of green algae in Adyar estuary and 4
species in Cooum estuary. Chandrashekara (2004) observed the dominance of
Closterium, Zygnema, Desmidium, Spirogyra, and Microspora in Sita-Swarna
estuary, Udupi.
In the present study except at station located at the confluence (station 1),
in remaining four stations Ulothrix was not only found in greater abundance but
also occurred more frequently, followed by Mougeotia, Pediastrum, Closterium,
Staurastrum and Zygnema.
The seasonal variation of total Chlorophyceae in the present study revealed
a dominant peak during monsoon season followed by secondary peaks in post-
monsoon season and a small rise in pre-monsoon season. It is only at station 1,
located at the confluence recorded a primary dominant peak in pre-monsoon
season followed by a small rise in monsoon and post-monsoon season. Therefore
from the data collected (Figure: 23 to 25), it can be stated that in Haladi-Chakra
estuary the abundance of green algae occurred more during monsoon season
followed by post-monsoon season. The seasonal variation observed in present
study is in agreement with the studies carried out by Mathew and Nair (1980),
Gowda et al. (2001c), Tripathi (2002) and Chandrashekara (2004).
5.6.1.3. Bacillariophyceae
In the present investigation, several species of Bacillariophyceae belonging to
26 genera were identified and numerical estimation have been made. The list of
26 genera of diatoms was presented in Table (18 to 22). Further the forms,
which occurred more frequently with greater abundance, have been depicted
graphically (Figure: 26 to 30). It is clear from the data that Chlorophyceae,
Cyanophyceae and Dinophyceae formed the bulk of phytoplankton community
next to Bacillariophyceae.
Mohanty (1975a) in Chilka lake and Joseph and pillai (1975) in Vellar
estuary have recorded the dominance of diatom during non-monsoon season.
Chandran (1985) and Mani et al. (1986) also observed greater abundance of
diatom in Vellar estuary. Mishra and Panigrahy (1995) in Bahuda estuary,
documented greater numbers of cell count of diatoms. Perumal et al. (1999)
observed greater abundance of diatoms in Vellar estuary. Similar dominance of
diatoms was also observed by Eswari and Ramani Bai (2002) in Adyar and
Cooum estuary.
Gopinathan (1975), Joseph and Pillai (1975), Mathew and Nair (1980),
Jayalakshmy et al. (1986) and Selvaraj et al. (2003) recorded dominance of
diatom during non-monsoon season in estuaries and backwaters of Kerala. In the
brackish water and estuarine environment of Dakshina Kannada, Nagarajaiah
(1980), Reddy (1982), Patil (1987), Puranik (1990), Bhattacharjaya (1991),
Gowda et al. (2001c), and Tripathi (2002) and Chandrashekara (2004) observed
the dominance of Bacillariophyceae in their investigation. While studying the
plankton distribution of Kali estuary, Karwar, Kusuma et al. (1988) recorded the
dominance of diatoms during pre and post-monsoon season.
A similar dominance of diatoms was observed by Devassy and Bhargava
(1978), Devassy (1983), Devassy and Goes (1988) and Redekar and Wagh (2000)
in Mandovi-Zuari estuary. Ramaiah et al. (1998) recorded the dominance of
diatoms in Thana-Bassein creek estuarine complex. Further, Krishnakumari et al.
(2002) while studying the primary productivity of Mandovi Zuari estuary of Goa,
recorded the dominance of diatoms.
In the present investigation at station 1 located in the confluence, species
of diatom belonging to 24 genera such as Biddulphia, Nitzschia, Coscinodiscus,
Ditylum, Rhizosolenia, Melosira, Chaetoceros, Campylodiscus, Pleurosigma,
Streptothecae and Fragillaria occurred more frequently with greater dominance.
During pre-monsoon season, the bulk of diatoms mainly consisted of Biddulphia,
Nitzschia, Coscinodiscus, Chaetoceros and Ditylum and these were responsible
for forming a primary peak in March. A smaller peak in May was formed mainly
due to higher numbers of Coscinodiscus, Biddulphia and Ditylum. In the monsoon
season, the diatoms such as Coscinodiscus, Rhizosolenia and Melosira formed the
monsoon peak. While during post-monsoon season, the Coscinodiscus,
Chaetoceros, Nitzschia, Ditylum, Fragillaria, Rhizosolenia and Melosira formed
the post-monsoon peak in November/December. From the data gathered (Table 18
to 22, and Figure: 26), it is evident that the diatoms exhibited by and large a
trimodal seasonal oscillation. The pre-monsoon peak was dominant than that of
the other peaks not only from the point of view of numerical abundance but also
richness of the diversity. A similar trimodal seasonal oscillation was observed at
stations located at confluence of Nethravati-Gurupur estuary and Sita-Swarna
estuary by Tripathi (2002) and Chandrashekara (2004) respectively.
At station 2 and 3, located in Haladi-Chakra estuary exhibited a primary
peak of diatoms in the month of February and March and species like Biddulphia,
Coscinodiscus, Cyclotella, Ditylum, Nitzschia, Pleurosigma along with
Rhizosolenia and Thalassiothrix, formed the bulk of this group. During monsoon
season, the diatoms such as Coscinodiscus, Melosira and Nitzschia were present
in moderate numbers especially from June to August and exhibited a monsoon
spurt along with Biddulphia and Pleurosigma in the month of September. During
post-monsoon season, they occurred with low to very low values during October
and November, the diatoms of this region exhibited post-monsoon peak during
December/January (Figure: 27 and 28). The peak was found to be consisting of
mainly Biddulphia, Coscinodiscus, Chaetoceros, Nitzschia, Pleurosigma along
with Rhizosolenia and Thalassiothrix. It is interesting to note that smaller cells of
Chaetoceros and Rhizosolenia were abundant in station 3 than that of station 2. So
this variation could be due to the impact of tides on small cells of diatoms.
Tripathi (2002) and Chandrashekara (2004) in the Nethravati-Gurupur
estuary and Sita-Swarna estuary observed bimodal seasonal oscillation
respectively. Further, they also recorded relatively greater number of diatoms at
stations situated away from the confluence. Similar spatial distribution was
observed in Haladi estuary.
At station 4 and 5, located in Chakra estuary exhibited pre-monsoon peak
in March and May. The bulk of the diatoms consisted of mainly Biddulphia,
Coscinodiscus, Chaetoceros, Ditylum, Melosira, Nitzschia and Pleurosigma.
During monsoon season especially between June and August the
composition of diatoms formed mainly of Biddulphia, Coscinodiscus, Ditylum,
Nitzschia, Pleurosigma and Campylodiscus with low to moderate numbers.
However, these diatoms along with Asterionella, Melosira, Cyclotella and
Streptotheca formed a monsoon peak in September. The post-monsoon peak in
Chakra estuary was observed in the month of December and January. This peak
was mainly consisted of Biddulphia, Chaetoceros, Coscinodiscus, Ditylum,
Pleurosigma, Nitzschia along with Fragillaria and Thalassiothrix. Therefore from
the data (Figure: 29 to 30), it is evident that the diatoms exhibited by and large a
trimodal seasonal oscillation by ignoring small peak, which was observed in May.
The numerical abundance in whole study region revealed greater
abundance and richness of diatoms in Haladi estuary followed by confluence and
Chakra estuary. This variation could be due to greater number of sand bars and
small mangrove islands in the Haladi riverine stretches. However, Tripathi (2002)
and Chandrashekara (2004) recorded an abundance of diatoms at stations located
near the confluence.
Nagarajaiah (1980), Reddy (1982), Puranik (1990), Gowda et al. (2001c)
and Tripathi (2002) observed bimodal seasonal oscillation of diatoms in
Nethravati-Gurupur estuary. However, Devassy and Bhargava (1978) in Mandovi-
Zuari estuary and Patil (1987) in Nethravati-Gurupur estuary observed trimodal
seasonal oscillation. It is interesting to note that Chandrashekara (2004) observed
trimodal oscillation of diatoms in Sita estuary and bimodal oscillation in Swarna
estuary.
In Kali estuary, Kusuma et al. (1988) observed bimodal cycle of yearly
abundance one during the pre and the other during post-monsoon periods.
Ramaiah and Nair (1998) in Bombay harbour-Thana and Bassein creek estuarine
complex observed greater abundance of diatoms during non-monsoon season.
However, Mathew and Nair (1980) observed primary peaks of phytoplankton
during monsoon season in Asthamudi estuary, Kerala. It is interesting to note that
a species of diatom belonging to genus Campylodiscus was recorded most of the
time at all the stations during pre-monsoon, monsoon and post-monsoon season
with smaller numbers. This species of diatom was first time recorded by Puranik
(1990) in Nethravati-Gurupur estuary, west coast of India.
5.6.1.4. Dinophyceae Studies on the occurrence and distribution of dinoflagellates are of great
value in fishery research, as several of these species are known to react to the
changes of the properties of water and hence used as indicator of water masses
and their movement. Further, various dinoflagellates are known to cause
discoloration of water towards red, green and yellow. While we have not much
information on the distribution of dinoflagellates in Indian waters, the systematic
studies on the seasonal and temporal distribution of dinoflagellates in estuarine
environment are scanty. In the present investigation, several species of
Dinophyceae belonging to 5 genera such as Ceratium, Peridinium,
Periperidinium, Noctiluca and Dinophysis were recorded (Table 18 to 22). Among
them Ceratium, Peridinium and Periperidinium were common and abundant.
Joseph and Pillai (1975), Santhanam et al. (1975) and Sundararaj and
Krishnamurthy (1975) have investigated the occurrence and distribution of
Dinophyceae in estuarine and coastal waters of India. The seasonal and temporal
variations of Dinophyceae in the estuaries of Dakshina Kannada coast were
observed by Nagarajaiah (1980), Pradeep (1980), Reddy (1982), Patil (1987),
Katti et al. (1988), Puranik (1990), Tripathi (2002) and Chandrashekara (2004).
The seasonal variation of Dinophyceae in station 1 located at confluence
indicated two peaks in March and May, which were mainly constituted by
Ceratium, Peridinium and Periperidinium. Ceratium occurred smaller numbers
formed a smaller monsoon peak from August. While post-monsoon peak was
observed in November/January, which mainly constituted by Ceratium and
Peridinium. Therefore from the data (Figure: 31 to 33), it is evident that
dinophyceae at this station exhibited by and large a tetra modal oscillation.
At station 2, located in Haladi estuary which is away from confluence
registered dominant peak in March consisting of Peridinium and Periperidinium
only and small peak in May which was mainly constituted of Ceratium,
Peridinium and Periperidinium. During monsoon season, the dinoflagellates were
present in meager numbers without exhibiting any peak. Noctiluca occur in
moderate number in September month. While in post monsoon season, a small
peak was observed in January, which consisted of only Peridinium. Therefore, it
can be stated that Dinophyceae at this station exhibited trimodal seasonal
oscillation.
At station 3, which is located nearer to the confluence, Dinophyceae
consisting of Ceratium, Peridinium and Periperidinium exhibited a clear cut
trimodal seasonal oscillation with peaks in March, May and January. Noctiluca
occur in higher number in September month.
At station 4, which is located in Chakra estuary the Dinophyceae
consisting of Ceratium and Peridinium exhibited a dominant peak in May. The
monsoon peak consisted of Ceratium, Noctiluca, Peridinium and Periperidinium,
which formed the peak in September. A predominant peak of Ceratium and
Peridinium formed in the month of December/January. Therefore, it can be stated
that the dinoflagellates at this station exhibited by and large a trimodal seasonal
oscillation.
At station 5, dinoflagellates consisting of Ceratium and Peridinium formed
the peaks of pre-monsoon, whereas only Ceratium was present in September
month in small numbers, while Ceratium and Peridinium formed the peak of post-
monsoon season in December.
The seasonal distribution of Dinophyceae in the region of study by and
large exhibited trimodal seasonal oscillation with two peaks in pre-monsoon
season and small peak in monsoon and post-monsoon season. The spatial
distribution revealed greater diversity richness at the confluence and stations
situated in Haladi estuary when compared to that of Chakra estuary.
While comparing the distribution of Dinophyceae with salinity and
temperature, it is evident that the population abundance of this group coincided
with the higher temperature and salinity regime of the year. Joseph and Pillai
(1975) stated that high temperature and salinity are favorable for better growth
and sustainance of dinoflagellates. Several workers such as Mathew and Nair
(1980), Reddy (1982), Kumar (1984), Patil (1987), Puranik (1990), Gowda et al.
(2001c) and Selvaraj et al. (2003) have recorded high concentration of
dinoflagellates in the estuaries and backwaters of Karnataka and Kerala during
pre-monsoon season. The present observation is in agreement with the above. The
smaller and secondary peak during post-monsoon season coincided with the
stepping up trend in salinity.
Kumar (1984), Patil (1987), Ramesh (1989), Puranik (1990) and Tripathi
(2002) observed the dominance Ceratium furca, C. tripos and C. extensum in the
estuarine and coastal waters of Dakshina Kannada. Same species were also
observed in the present investigation. Among them Ceratium furca dominated
through out the pre-monsoon season. A detailed study was carried out by
Ilangovan (1987) on the diversity and distribution of Dinophyceae in Vellar
estuary, which revealed the dominance Ceratium furca, C. tripos and C. extensum.
In the present study the bulk of dinoflagellates consisted of Ceratium,
Periperidinium, Peridinium and Noctiluca. Among the three species of Ceratium,
Ceratium furca was dominant followed by C. tripos and C. extensum. Similar
dominance of Ceratium furca was observed by Tripathi (2002) in Nethravati-
Gurupur estuary and Chandrashekara (2004) in Sita-Swarna estuary.
The relationship between salinity and total phytoplankton counts revealed
greater abundance of phytoplankton in mixoeuhaline condition of water during
pre-monsoon season. During post-monsoon season, the abundance with moderate
numbers coincided with polyhaline condition. The spatial distribution revealed a
greater abundance of total phytoplankton at station 2 in Haladi estuary and station
1 at confluence region during both pre and post-monsoon season (Figure: 60).
During pre-monsoon season, the higher density of phytoplankton was
found to be coincided with mixoeuhaline condition of water, where the salinity
was more than 30 ppt and less than the adjacent seawater. Whereas during post-
monsoon season, the peaks during December and January was found to be
coincided with holohaline condition, where salinity ranged between 11 ppt and 30
ppt (Figure: 60). In the present study most of the forms, which have exhibited
peak abundance during pre-monsoon season were also found to be exhibiting
another peak during post-monsoon season. Therefore, it is clear that mixoeuhaline
condition is optimum for the vigorous growth of phytoplankton in this estuary.
However, few forms were found to tolerate polyhaline condition which existed
during later half of monsoon season and post-monsoon season. Qasim (1980)
observed higher density of diatoms in the salinity ranges of 10-20 ppt in Cochin
backwater. Patil (1987) and Puranik (1990) documented abundance of diatom
cells in mixoeuhaline condition in Nethravati-Gurupur estuary.
The relationship between Phosphate-phosphorus and total phytoplankton
cells and Nitrate-nitrogen and total phytoplankton cells revealed inverse
relationship (Figure: 61 and 62).
The lower concentration of phosphate, which also coincided with greater
abundance of phytoplankton (Figure: 61), suggests that the low values of
phosphate during the pre-monsoon season could also be due to greater utilisation
of this plant nutrient.
The lower concentration of nitrate, which coincided with greater abundance of
phytoplankton, suggests that the low values of nitrate during the pre-monsoon
season could be due to greater utilisation of this plant nutrient. During
monsoon season, nitrate concentration was high compared to total
phytoplankton cells because lower numbers of phytoplankton cells were unable
to utilize the higher concentration of nitrate nutrient. However, higher
concentration of nitrate and moderate density of phytoplankton during post-
monsoon season could be due to poor utilization of nitrate and high input of
nitrate (Figure: 62).
Similar relationship between phosphate and diatom cell numbers were
observed by Puranik (1990), Gowda et al. (2001c) and Tripathi (2002) in
Nethravati-Gurupur estuary. In the present investigation, relationship between
chlorophyll-a and total phytoplankton cells could not be established. Suresh
(1987), Mathew (1994), Tripathi (2002), and Chandrashekara (2004) did not
observe any relationship between chlorophyll-a and phytoplankton.
5.7. Zooplankton Zooplankton forms an important and integral component of ecosystem by
virtue of its special position in the food chain. The qualitative and quantitative
distribution of zooplankton in space and time are often used as an index for
predicting the fishery potentiality of an environment. According to Shetty et al.
(1961) and Madhupratap (1981) there exists a relationship between zooplankton
and fisheries. The distribution of zooplankton is always patchy and dynamic.
This dynamic nature gets further complicated in an environment like estuaries due
to the influence of tide. Further, the changes in the community structure and
quality of zooplankton reflect the quality of the estuarine waters.
5.7.1. Qualitative distribution 5.7.1.1. Medusae and siphonophores
Hydromedusae form an important ecological category in the plankton
ecosystem because of their specialized position as exclusively carnivores
component in the marine food chain. The hydromedusae greatly contribute to the
volume and biomass of the total plankton.
In the present investigation, only few forms of medusae belonging to
genera Philadilium sp., Eutiama sp. and Erene sp. along with medusoid stages,
benthic hydroids such as Obelia sp. and Cordilophora sp. were observed. The
siphonophores were found to species belonging to the genera Lensia sp. The
number of medusae varied from 01 to 1663 No/m3 and siphonophores from 01
No/m3. From the Table 23 and Figure 34, it is evident that the abundance of
medusae were more in post-monsoon season followed by pre-monsoon and
monsoon season. The higher number was recorded in August at confluence region
(station 1). Whereas siphonophores occurred in meagre numbers only in May.
The abundance of hydromedusae at confluence region dominants the stations
located in Haladi and Chakra estuary. The dominant of medusae at confluence is
due to the greater abundance of these groups in the adjoining coastal waters.
Further, they could easily get transported through the bar mouth during high tide
and entered in the estuarine basin.
Vanucci (1977) while working on the hydromedusae in the Cochin
backwaters observed rich and varied population of hydromedusae during pre-
monsoon season when salinity was relatively higher. However, Bhat (1979)
recorded fairly good number of hydromedusae in December and January in
Gurupur estuary of Dakshina Kannada. Patil (1987) documented higher
abundance of medusae during post-monsoon season in Nethravati estuary and
during pre-monsoon season in Gurupur estuary. While working on zooplankton
ecology, Padmavathi and Goswami (1996) observed higher number of
hydromedusae during pre-monsoon season when temperature and salinity were
higher. Sujatha and Panighray (1999) recorded abundance of medusae during
post-monsoon season in Bahuda estuary (Orissa). The present observation is in
agreement with the observation made by Bhat (1979), Patil (1987) in Nethravati-
Gurupur estuary and Sujatha and Panighray (1999) in Bahuda estuary (Orissa).
However, the study carried out by Santhakumari et al. (1999) revealed abundance
of hydromedusae during post-monsoon season in Dharmatara estuarine system.
Vijay Kumar (2002) observed the abundance of hydromedusae during pre-
monsoon season and moderate number in post-monsoon season in Nethravati-
Gurupur estuary. Vikas (2004) recorded the meager number of hydromedusae in
pre-monsoon season in Sita-Swarna estuary, Udupi.
While comparing the abundance of hydromedusae in present study with
that of Nethravati-Gurupur estuary and Mulki estuary, revealed that the abundance
and distribution of this group along with siphonophores is much lower. This low
density could be due to lesser intensity of transportation from the adjoining coastal
waters or in ability to colonise due to shallowness and high turbidity in this
estuary.
5.7.1.2. Ctenophores Not much data is available on the seasonal distribution of ctenophores in
brackish water environment. However, instance of occurrence have been reported
by several planktonologist working in different brackish waters of India. In the
present study, Pleurobranchia sp. and Mnemiopsis sp. were the sole
representatives of this group. While the Mnemiopsis sp. occurred only in
April/May, the number of which varied from 01 to 02 No/m3 nearer to the bar
mouth, while Pleurobranchia sp. varied from 01 to 02 No/m3 with sporadic
occurance in pre-monsoon season. In post-monsoon season, it occur in December/
January month. It is clear from the Figure 35 and Table 24, that the abundance of
Pleurobranchia sp. was observed maximum during monsoon season. It is
interesting to note that the greater abundance of Pleruobranchia sp. was found in
stations located near to the Haladi estuary and the stations located near the
confluence. The numerical abundance in Chakra estuary was lower when
compared to Haladi estuary. Further, it was observed that the Pleurobranchia sp.
were abundant during monsoon season suggesting that the Pleurobranchia sp.
breed in the adjoining coastal waters immediately after the monsoon season, when
salinity was at moderate levels. Further, the Pleurobranchia sp. occurred in
March/April were all adults with mature gonads.
In Cochin backwaters, Rao et al. (1975) and Madhupratap and Haridas
(1975) recorded higher number of ctenophores. During pre-monsoon season, Bhat
(1979) observed higher number of planktonic carnivore forms during February
and March in Nethravati-Gurupur estuary. However, Patil (1987) recorded fairly a
good number of Pleurobranchia sp. in October and December in the same estuary.
Puranik (1990) documented higher abundance of ctenophores during pre-monsoon
season and were totally absent during post-monsoon season. Peak abundance of
Pleurobranchia sp. in Mandovi-Zuari estuary was observed by Padmavathi and
Goswami (1996) in April. Sujatha and Panigrahy (1999) recorded the occurrence
of ctenophore in April in Bahuda estuary (Orissa). Vijay Kumar (2002) while
studying the distribution of zooplankton in relation to selected hydrographical
parameters in Nethravati-Gurupur estuary observed the greater abundance of
ctenophores in pre-monsoon and post-monsoon season. Vikas (2004) recorded
sporadic numbers of ctenophores throughout the study period and observed
maximum abundance during post-monsoon season in Sita-Swarna estuary, Udupi.
In the present investigation, the period of occurrence and seasonal distribution of
ctenophores was dominated in pre-monsoon and monsoon season found to be
slightly different from that of the study made by different workers in Nethravati-
Gurupur and Mulki estuaries.
5.7.1.3. Chaetognaths and chaetognath larvae
Chaetognaths form an important constituent of marine and brackish water
zooplankton community. Its predatory habit, totally isolated group from main
stream and as an indicator species of water masses has been made it a subject of
intense research.
In the present study, the number of chaetognaths varied from 01 to 51
No/m3 and chaetognath larvae varied from 01 to 1104 No/m3 (Table 25). The
qualitative composition of this group revealed the presence of Sagitta beloti, S.
setosa, S. enflata, S. polchra and Eokonia sp. Among them, most dominant were
S. beloti and S. pulchra. Similar observation was made by Padmavathi and
Goswami (1996) in Mandovi-Zuari estuary, Goa, Sujatha and Panigrahy (1999) in
Bahuda estuary, Orissa, Pattanaik and Sarma (1997) in Chilka lake, Vijay Kumar
(2002) in Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary
respectively.
In the present study, chaetognaths were present most of months during
post-monsoon season and were totally absent in April month of pre-monsoon
season except at station 4. In monsoon season, it occur in August and September.
The pre-monsoon peak observed in March except at station 4 and the post-
monsoon peak was noted in October at near confluence and Haladi estuary. The
pre-monsoon peak was more dominant than that of post-monsoon peak in Haladi
estuary. Whereas at confluence and Chakra estuary, the post-monsoon peak was
dominant (Figure: 36). The frequency of occurrence and the numerical abundance
was more at the confluence and Haladi estuary compared to Chakra estuary. In the
Chakra estuary the stations which are located away from the confluence registered
were low numbers of chaetognaths with less frequency.
The chaetognath larvae in the present study occurred almost all the months
accept in April month of pre-monsoon season. The pre-monsoon peak was
observed in February/March, monsoon peak in August (station 1, 3 and 4) and
September month (station 2 and 5), and the post monsoon peak was recorded in
October except at station 1 (Figure: 37). The post-monsoon peak was more
dominant than that of pre-monsoon peak in Haladi-Chakra estuary, but station
near the confluence the monsoon peak was dominant the pre-monsoon and post-
monsoon peaks. From the data gathered, it is known that the stations at the
confluence and the Chakra estuary exhibited higher frequency of occurrence of
chaetognath larvae than that of Haladi estuary. The spatial distribution of
chaetognath and chaetognath larvae in the present study is influenced by
topography of the estuarine basin, which could possible make free flow of tidal
waters to the estuarine region.
Patil (1987) recorded higher number of chaetognaths in Gurupur estuary
than that of Nethravati. Working on the ecology of chaetognaths, Nair and Selva
Kumar (1979) reported presence of more number of species in Zuari estuary than
that of Mandovi-Zuari estuary.
Abundance of chaetognaths during pre and post-monsoon season were
observed by Bhat (1979), Patil (1987), Puranik (1990) and Vijay Kumar (2002) in
Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary respectively.
Padmavathi and Goswami (1996) recorded higher abundance of chaetognaths
during pre-monsoon and post-monsoon season in Mandovi-Zuari estuary, Goa.
However in the estuaries along east coast of India, Sarkar et al. (1985) observed
greater abundance during June/July, while Pattanaik and Sarma (1997)
documented greater abundance during July/August. While comparing the
occurrence and distribution of chaetognaths and salinity conditions, it becomes
evident that occurrence and distribution of chaetognaths in these estuaries were
mainly controlled by the intrusion of saline water in to the estuarine region.
Similar observations were made by earlier workers along both the coast of India.
The present observation is in agreement with the works carried out by earlier
authors.
The pre-monsoon abundance of larval forms of chaetognaths suggests the
presence of larval forms in greater numbers in the adjoining coastal waters.
Similar type of larval distribution was observed by Menon et al. (1977) in the
coastal waters of Mangalore, Vijay Kumar (2002) in Nethravati Gurupur estuary
and Vikas (2004) in Sita-Swarna estuary, Udupi respectively.
5.7.1.4. Polychaetes and polychaete larvae
Polychaetes and polychaete larvae forms an important component in
plankton samples of estuarine and coastal waters. Therefore, almost all the
workers documented the occurrence and seasonal distribution while working on
the ecology of estuaries, backwaters and coastal environment.
In the present study, the number of polychaetes fluctuated varied from 01
to 16 No/m3 and polycheate larvae from 01 to 19253 No/m3 (Table 26). The
works carried out by Pillai and Pillai (1975), Madhupratap (1978), Rao et al.
(1985) and Nair et al. (1984) revealed a greater abundance of polychaete larvae
formed an important component in the zooplankton samples collected from
various brackish water environment of Kerala coast. Similar kind of observations
were made by Reddy (1977), Bhat (1979), Nagarajaiah (1980), Reddy (1982),
Patil (1987), Puranik (1990), Vijay Kumar (2002) and Vikas (2004) in various
brackish waters of Dakshina Kannada and Sita-Swarna estuary, Udupi
respectively. The occurrence and distribution of polychaete larvae in Mandovi-
Zuari estuary was studied by Goswami et al. (1979). In Kali estuary, Kusuma et
al. (1988) recorded the occurrence of polychaete larvae. Padmavathi et al. (1997)
recorded small numbers of polycheate larvae in Mandovi-Zuari estuary, Goa.
Srikrishnadas and Ram Moorthi (1982) reported the dominance of polychaete
larvae in Porto Novo waters. While studying on the zooplankton ecology of
Rushikuliya estuary, Gouda and Panigrahy (1995) documented the greater
abundance of polychaete larvae. Mishra and Panigrahy (1999) observed the
presence of polychaete larvae except during flooding season in Bahuda estuary.
In the present study, the seasonal distribution of polychaetes revealed
lesser number in pre-monsoon season. They were completely absent in the month
of June, July and August month of monsoon season. The monsoon peak was
observed in September month at confluence region (station 1). The polychaete
were totally absent during post-monsoon season at station 5. The post-monsoon
peak was observed in the month of October in station 1 and 2 and November in
station 3, but the moderate peak was observed in station 4. The polychaetes in the
present study revealed more numbers at confluence than Haladi and Chakra
estuary. The post monsoon peak was more dominant than pre-monsoon and
monsoon peak except at station 4 (Figure: 38).
In the present study, the polychaete larvae occurred almost throughout the study
except station 4 in July month. The seasonal fluctuation of the larvae revealed
presence of higher numbers during pre-monsoon season with a peak in February at
all stations. The monsoon peak was observed in gradual increase in the month of
June/July and occurred its maximum in August forming the secondary peak. The
post-monsoon peak was observed in January month at all the stations. From the
Figure 39, it is evident that the polychaete larvae exhibited trimodal seasonal
oscillation. The pre-monsoon peak dominant the post-monsoon peak and monsoon
peak in almost all the stations.
It was observed that most of this polychaetes and polychaete larvae are
benthic forms but occurred in the plankton sample because of the shallow nature.
The presence of polychaete larvae throughout the study period suggests the
polychaete of this region breed continuously. Therefore, it could be stated that the
salinity is the prime factor in influencing the breeding periodicity of the
polychaete and polychaete larvae. The maxima during the pre-monsoon season
was observed with the con-comitant (simultaneously) increase in the salinity.
Bimodal seasonal oscillation was recorded by Menon et al. (1977), Eknath
(1978), Patil (1987), Puranik (1990) and Bhat (1979) in the coastal waters and
Nethravati-Gurupur estuary, Mangalore. However, Reddy (1982) in Mulki
estuary could not observe clear-cut seasonal fluctuation of this larvae. Vijay
Kumar (2002) observed higher abundance of this larvae during pre and post-
monsoon season and opined that the salinity is the major factor influencing the
breeding of polychaetes in the coastal waters and Nethravati-Gurupur estuary.
Vikas (2004) documented the seasonal distribution of polychaetes revealed higher
numbers in April exhibiting a single dominant peak during pre-monsoon season.
Similar opinion was drawn by Madhupratap and Haridhas (1975) in Cochin
backwaters and Patil (1987) and Puranik (1990) in Nethravati-Gurupur estuary.
Quality composition of polychaete and polychaete larvae revealed that
most of them were belong to family Neridae, Nepthidae, Glyceridae,
Sabellaridae, Arenicola and Maladanidae. Among them, larvae of Nepthidae,
Neridae and Glyceridae form the bulk of the polychaete larvae throughout the
period of investigation. In the present study, the polychaete and polychaete larvae
were more dominant in stations at and near to the confluence than away from it.
However, Vijay Kumar (2002) observed greater abundance of larvae in Nethravati
than that of Gurupur estuary. Vikas (2004) could not observe any spatial variation
in the Sita-Swarna estuary, Udupi.
5.7.1.5. Cladocera
Cladocerans attracted the attention of many marine biologist and fishery
scientist because of an intimate relationship with pelagic fisheries (Selva Kumar,
1970) and its high reproductive potentiality through parthenogenesis resulting in
spurt at times and total absence at other times (Dellacroce and Venugopal, 1972).
This group was mainly represented by Penilia avirosteris and Evadne tergestina.
In the present study, Penilia sp. number varied from 133 to 28858 No/m3
(Table 27), but they were absent in June/ July month except at station 2. The pre-
monsoon peak was observed in April except at station 5 (March) and station 1
(February). The monsoon peak was observed in August at station 1 and station 2
and September in station 4. At station 3 and 5, it occurs in meager numbers. In
post-monsoon season, the dominant peak was observed in the month of October at
station 1 and 2 and December in station 3, 4 and 5 (Figure: 40). The post-
monsoon peak dominant the pre-monsoon peak. The confluence region registered
the more numbers than Haladi-Chakra estuary.
The Evadne sp. during the present study fluctuated from 133 to 6412
No/m3 (Table 27). The pre-monsoon peak was observed in February at almost all
the stations except at station 2 (April). The monsoon peak was not clearly
exhibited (Figure: 41), but it attains maximum in August (station 1, 2 and 5) and
September (station 3 and 4). The post-monsoon peak was noted in October
(station 1 and 2) where has it attains maximum peak in December (station 3, 4
and 5). During the present study, the Evadne sp. dominant in pre-monsoon and
post-monsoon season. The frequency of occurrence and the numerical abundance
shown at confluence and Chakra estuary were more dominate than that of Haladi
estuary.
Both the species exhibited almost similar trends of occurrence and
abundance, but variation in their dominant peaks. However, the investigations
made by Patil (1987), Puranik (1990) and Vijay Kumar (2002) indicated the
dominance of Penilia avirosteris at salinity values of 3.50 to 31.20 ppt in
Nethravati-Gurupur estuary. Vikas (2004) observed the dominance of Penilia
avirosteris and Evadnae tergestina in Sita-Swarna estuary, Udupi.
Goswami (1992) documented few cladocerans in mangrove ecosystems of
Goa. Gouda and Panigrahy (1995) observed few numbers of cladocerans in
Rushikulya estuary, Orissa. Pattanaik and Sarma (1997) documented sporadic
occuranceof cladocerans in Chilka lake. Chandramohan and Sreenivas (1998)
did not observe cladocerans in the mangrove areas of Gaderu canal south east
coast of India. Mishra and Panigrahy (1999) observed the abundance of
cladocerans in Bahuda estuary, Orissa.
A critical look at the seasonal variation of this group revealed a gradual
increase in number from February to April and total absence in June and July.
Further, the population exhibited second increase in August/September which
gradually increased during later half of post-monsoon season and attain maximum
peak in October/December. From Figure 40 and 41, it is evident that the
cladocerans exhibited bimodal seasonal oscillation. It is interesting to note that
cladocerans were abundant in high saline of waters (February/April) and also
when the salinity was moderate during September/October and December.
Goswami and Selvakumar (1977) reported the dominance of Evadne
tergestina in the salinity range of 0.21 to 1.67, while Penilia avirosteris in the
range of 19.31 to 33.95 ppt. In the present study, Evadne tergestina were
observed in the salinity range of 0.14 to 32.69 ppt and Penilia avirosteris in the
salinity range of 9.49 to 33.00 ppt. The seasonal variation of this group and the
water temperature revealed that the pre-monsoon abundance coincided with
highest water temperature. While post-monsoon abundance coincided with
gradual increase of surface waters. Goswami and Devassy (1991) observed a
wide range of salinity tolerance by cladocerans in Mandovi-Zuari estuary.
Padmavathi and Goswami (1996) reported the abundance of cladocerans at lower
temperature and salinity values in Mandovi-Zuari estuary. In the present study, the
period of occurrence and seasonal distribution of Cladocerans was found to be
similar observation made by Vijay Kumar (2002) and Vikas (2004) in Nethravati-
Gurupur estuary and Sita-Swarna estuary respectively.
5.7.1.6. Cirripede larvae The occurrence of cirripede larvae (nauplius and cypris) would give an
idea about the breeding of barnacle present in the environment. In the present
study, barnacle nauplii varied from 22 to 1657 No/m3 and barnacle cypris ranged
from 01 to 08 No/m3. Cypris larvae were present at two instances one in August
(station 1) and September (station 4). The greater abundance of barnacle nauplii
were present almost all the stations during the pre and post-monsoon season. The
greater abundance of barnacle nauplii were observed in pre-monsoon and post-
monsoon season (Table 28). It is evident from the Figure 42, that the pre-monsoon
peak abundance is different in different months. It shows peaks in February month
(confluence and Haladi estuary) and March month (Chakra estuary). The monsoon
peaks was observed in August month. Whereas the post-monsoon peak was
noticed in October (station 1, 3 and 4) and November (station 2 and 5). Therefore,
it could be stated that the barnacle nauplii exhibited a trimodal seasonal
oscillation. The spatial distribution revealed greater abundance in Haladi estuary
than that of Chakra estuary and confluence region during post-monsoon season.
While during pre-monsoon and monsoon season, the stations at Chakra estuary
exhibited greater abundance than Haladi estuary and confluence region. The low
number in monsoon season was due to low saline conditions.
Patil (1987) recorded a few barnacle nauplii during later part of monsoon
season at station located near the bar mouth in Nethravati-Gurupur estuary.
Similar kind of observation was made by Puranik (1990) in the same environment.
Vijay Kumar (2002) while studying the distribution of zooplankton observed less
number of barnacle nauplii in October/November, when the salinity of water was
very low. Vikas (2004) observed the trimodal seasonal oscillation in Sita-Swarna
estuary, Udupi. The presence of cirripede larvae of greater numbers was observed
in Sita estuary than that of Swarna and confluence during pre-monsoon season.
Bimodal seasonal oscillation of barnacle nauplii was reported by Bhat
(1979), Nagarajaiah (1980), Reddy (1982), Patil (1987), Puranik (1990) and Vijay
Kumar (2002) in the Nethravati-Gurupur estuary and brackish water environment
of Dakshina Kannada.
In the present study, three maxima of barnacle nauplii in pre and post-
monsoon season coincided with high salinity conditions which suggest that the
breeding of barnacles in the area is controlled by salinity conditions of the
environment. From the Figure 42, it is evident that the nauplii were totally absent
in the month of June/July at confluence, due to the dominant of freshwater inflow
from estuary to the confluence region in monsoon season. The rich abundance of
barnacle nauplii throughout the season is influenced by availability of right type of
food for the nauplii and recruitment to the estuary from adjoining coastal waters.
5.7.1.7. Copepods
In the present investigation, copepods formed the bulk of the total
zooplankton and also present throughout the period of study at all the stations. A
greater abundance of copepods in the plankton sample collected from various
estuaries along east coast of India was reported by Mohan (1977), Baidya and
Choudhury (1984), Mohamed and Rahaman (1987), Sarkar et al. (1986) Sarkar
and Choudhury (1988), Gouda and Panigrahy (1995), Chandra Mohan and
Sreenivas (1998) and Misra and Panigrahy (1999).
Along the west coast, Goswami (1982), Bhat and Gupta (1983),
Nagarajaiah and Gupta (1985), Nair and Azis (1987), Thompson (1991), Nandan
and Azis (1994), Neelam-Ramiaha and Nair (1997), Padmavathi et al. (1997),
Vijay Kumar (2002) and Vikas (2004) recorded the dominance of copepods in the
plankton sample collected from various estuaries.
During the present study, the copepod ranged from 3867 to 180632 No/m3.
It is clear from the Figure 43 and Table 29 that the abundance of copepods in this
estuary was in the month of February/May of pre-monsoon season. During
monsoon season, population density of copepods declined at all the stations and
gradually increased in September. An increasing trend was observed during post-
monsoon season with two small peaks during November/January except at station
1 (October/ January).
A general decline during the period of intense rainfall has been reported in
several estuaries and backwaters of east coast of India. [Sundararaj and Krishna
Murthy (1975), Shanmugham et al. (1986), Sujata and Panigrahy (1996),
Pattanaik and Sarma (1997) and Misra and Panigrahy (1999)]. A similar decline
was observed by mainly workers while studying the distribution of plankton in
various brackish waters environment of Kerala, Dakshina Kannada and Goa. [Rao
et al. (1975), Madhupratap et al. (1977), Nair et al. (1984), Bhat (1979),
Nagarajaiah (1980), Reddy (1982), Patil (1987), Goswami (1983), Puranik (1990),
Tiwari and Nair (1993), Padmavathi and Goswami (1996) and Musthafa (1999)].
The pre-monsoon and post-monsoon abundance is found to be more than
monsoon peaks at almost all the stations during the present study. The September
month dominant the monsoon season.
Silas and Pillai (1975) documented greater abundance of copepods during
pre-monsoon in backwaters of Kerala. Patil (1987) in Nethravati-Gurupur estuary
observed greater abundance during pre-monsoon and moderate abundance in post-
monsoon season. However, Bhat (1979) observed variation in magnitude in pre
and post-monsoon at different stations. Puranik (1990) and Vijay Kumar (2002)
observed greater abundance during pre-monsoon season in the same estuary.
Vikas (2004) observed the pre-monsoon abundance was found to be more than
that of post-monsoon at all most all the stations. In Mandovi-Zuari estuary,
Padmavathi and Goswami (1996) reported greater abundance of copepods during
pre-monsoon season.
In the present investigation, the spatial variation of copepods showed
higher density at stations located away from the confluence. The occurrence and
abundance of copepods in Haladi estuary is more than that of Chakra estuary.
Based on salinity tolerance, copepods can be categorised into three distinct types;
one booming in mixoeuhaline conditions prevailed during pre-monsoon, the
second group thriving in limnetic condition during monsoon season and the third
category affluent polyhaline condition of the water prevailed during post-monsoon
season (Table 29).
Patil (1987), Puranik (1990) and Vijay Kumar (2002) have observed the
two types of copepods; one booming mixoeuhaline condition and the other in
polyhaline conditions in Nethravati-Gurupur estuary.
The quality composition of copepod community revealed the presence of
various species belonging to genera Acartia, Paracalanus, Pseudodiaptomous,
Centrophages, Microsetella and Euterpina. The group Cyclopoidae consisted of
species belonging to Oithona, Corycaeus, Oncae, Cyclops and Diaptomous.
Among the three different forms of copepods, Cyclopoidae and Herpecticoidae
dominated the samples collected during monsoon season. While pre-monsoon
samples contained copepods belong to group calanoidae and cyclopoidae. By and
large, similar composition of copepod population was observed by Patil (1987),
Puranik (1990) and Vijay Kumar (2002) in Nethravati-Gurupur estuary and Vikas
(2004) in Sita-Swarna estuary respectively. Neelam-Ramaiaha and Nair (1997)
recorded dominance of calanoid copepods in Bombay harbour-Thana and Bassein
creek west coast of India. Similar dominance of calanoid copepods in Bahuda
estuary was observed by Mishra and Panigrahy (1996). Mohamed and Rahman
(1987) observed greater abundance of Oithona sp. throughout the year in Agniar
estuary Tamilnadu. Gaughan and Potter (1995) observed dominance of Oithona
and Acartia in a shallow, seasonally closed estuary in temperate Australia.
However, Pattanaik and Sarma (1997) documented the presence of calanoid and
cyclopoid copepods throughout the sampling period. Whereas the herpecticoids
were present during October and December in Chilka lake.
5.7.1.8. Copepod larvae In the present investigation, copepod larvae comprised of various nauplius
stages and copepodite stages and their numbers ranged from 552 to 44335 No/m3
(Table 30). The presence of fairly good number of larvae during pre- and post-
monsoon suggests that the copepods in this area breed in both the seasons.
However, seasonal distribution of this larvae revealed greater abundance in March
(Haladi-Chakra estuary) and February (confluence). A gradual decreasing trend
was observed in the monsoon season and increasing trend was noticed in
September month formed the secondary peak. In post-monsoon season, the greater
abundance was noticed in January form the third peak. Therefore from the Figure
44, it is evident that this larvae exhibit trimodal seasonal oscillation. The seasonal
variation in population density of this larvae exhibited pre-monsoon and post-
monsoon season dominant the monsoon season. The peak density of adult
copepods during pre and post-monsoon seasons almost coincides with abundance
of copepod larvae, a similar type of observation was made by Vijay Kumar (2002)
in Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary.
High abundance of copepod larvae during pre-monsoon season in the
coastal waters of Mangalore was observed by Menon et al. (1977), Benakappa et
al. (1979) and Ramesha (1989). In Nethravati-Gurupur estuary greater numbers
of these larvae during pre-monsoon season was observed by Bhat (1979),
Nagarajaiah (1980), Patil (1987) and Puranik (1990). While comparing the
seasonal variation of larvae with that of salinity, it becomes clear that copepods
exhibit intense breeding in specific salinity region such as mixoeuhaline during
pre-monsoon season and moderate breeding in polyhauline condition prevailed
during post-monsoon season.
5.7.1.9. Luciferidae
Luciferidae is chiefly represented by Lucifer hanseni, a common sergisted
occurring in the estuarine system of both the coast of India. According to Omare
(1977), this group forms a major component of the diet of fishes and shrimps.
Thus, it plays an important role in the food web of estuaries and coastal waters.
In the present study, the number of adult lucifers dominant the lucifer
larvae. These decapods were present sporadically with small numbers varying
from 01 to 61 No/m3 (Table 31). The seasonal distribution revealed the presence
of higher numbers in May of pre-monsoon season and were completely absent in
April month. In monsoon season, they were dominant in September month, but
they were not found in June and July. In Post-monsoon season, they were occur
only in two instances in October (station1 and 4). They were completely absent in
remaining months. From the Figure 45 and 46, it is clear that pre-monsoon
abundance was more dominant than the post-monsoon season. Further, it is
revealed that the more number of lucifers were present at stations situated away
from the confluence.
Menon et al. (1977), Goswami and Selva kumar (1977), Suresh and Reddy
(1975), Benakappa et al. (1979) and Patil (1987) observed a bimodal seasonal
oscillation in nearshore waters of Goa and Dakshina Kannada. Padmavathi and
Goswami (1996) documented maximum number of lucifer in April in Mandovi-
Zuari estuary. Pattanaik and Sarma (1997) recorded a greater number of lucifers in
April in Chilka lake. The present observation of greater numbers of lucifers in
May is in agreement with the works of above authors. However, Patil (1987) and
Puranik (1990) observed greater number of lucifers during October/ November
and the authors have opined that the greater number during this season was due to
the presence of higher numbers of these larval forms. Vijay Kumar (2002)
observed low density of lucifers in Nethravati-Gurupur estuary. In the present
study, lucifers with high numbers during pre-monsoon and very low to negligible
numbers during post-monsoon is found to be in agreement with the investigation
made by Vijay Kumar (2002) in Nethravati-Gurupur estuary. Very few numbers
of lucifer larvae were observed in March/April and were totally absent during
remaining part of the year. Vikas (2004) observed the greater numbers of lucifers
in April and May and were totally absent in July/August. Very few numbers were
recorded in November /January in Sita-Swarna estuary.
5.7.1.10. Decapod larvae Decapod forms an important fishery along both the coast of India. As a
result, a great deal of information is available on the occurrence, distribution and
biology of various decapods. However, the seasonal and spatial distribution of
decapod larvae as separate group among the total zooplankton community is
found to be scanty. In the present investigation, different types of decapod larvae
such as shrimp nauplii, protozoea, post larvae of shrimp, zoea, mysis, megalopa
and elima have been observed and documented in Table 32. Among the 7 larval
groups observed 4 groups such as post larvae of shrimp, protozoea, zoea, and
mysis and have been depicted graphically in Figure 47 to 50. Large number of
decapod larvae were observed by Silas and Pillai (1975), Kuttyamma (1975), Nair
et al. (1984) in Cochin backwaters. Menon et al. (1977), Bhat (1979),
Nagarajaiah (1980), Reddy (1982), Kumar (1984), Patil (1987), Puranik (1990),
Ronald (2001) and Vijay Kumar (2002) documented the occurrence and
distribution of decapod larvae in the nearshore waters in Nethravati-Gurupur
estuary, Dakshina Kannada and Vikas (2004) in Sita-Swarna estuary respectively.
Occurrence and distribution of penaeid larvae in estuarine waters of Goa
was reported by Goswami and George (1978), Achuthankutty (1987), Goswami
and Goswami (1992). In the same environment, Padmavati and Goswami (1996)
observed higher abundance of decapod larvae next to copepods. In the estuaries
along east coast of India, Gajbhiye (1981), James (1987), Pattanaik and Sarma
(1997) and Misra and Panigrahy (1999) documented higher numbers of decapods.
In the present study, shrimp nauplii varied from 01 to 02 No/m3 (Table
32). They were completely absent in station 1 (confluence region). They were
occurring in meager numbers in May/July in station 2. Lesser number of shrimp
nauplii were observed during March/ September in station 3. At station 4, they
were occurred in February/March and May. At station 5, it is occur in one
instances in May month and absent in remaining months at all stations. However,
Vijay Kumar (2002) observed abundance of shrimp nauplii in the high tide phase
during March in Nethravati-Gurupur estuary. Goswami and Goswami (1992)
observed lesser number of shrimp nauplii in the Mandovi-Zuari estuary. Ronald
(2001) recorded moderate number of shrimp nauplii during pre-monsoon season at
the confluence region of Nethravati-Gurupur estuary. Vikas (2004) recorded lesser
number of shimp nauplii during pre-monsoon and post-monsoon season in some
stations in Sita-Swarna estuary.
The post larvae of shrimp were present at all station and the number varied
from 01 to 10 No/m3 (Table 32). The seasonal distribution revealed presence of
higher number in February (station 3) and October/ November (station 2). The
larvae were observed during monsoon season at all the months at confluence
(station 1). They were occur in lower numbers in other stations. A small post-
monsoon peak was observed at October/November. From the Figure 47, it is
evident that the larvae were dominant in post-monsoon season. The spatial
variation revealed stations at confluence and Haladi estuary exhibit more numbers
than that of Chakra estuary. The pre-monsoon abundance coincided with
mixoeuhaline condition and the post-monsoon occurance coincided with
polyhauline condition. Between the two brackish water conditions, this larvae
preferred mixoeuhaline condition than that of polyhaline condition. Similar
observations were made by Goswami and Goswami (1992) in Mandovi-Zuari
estuary, Ronald (2001) and Vijay Kumar (2002) in Nethravati-Gurupur estuary
and Vikas (2004) in Sita-Swarna estuary respectively.
Protozoea stages were mainly belonging to lucifers and shrimps. The
seasonal distribution revealed the presence of this larvae in February and
September at all the stations (Figure: 48). The numbers of larvae varied between
01 to 801 No/m3. During the other stations they were totally absent in the
April/June and July month in this environment. In the Nethravati-Gurupur estuary,
Patil (1987) and Vijay Kumar (2002) recorded trimodal seasonal oscillation with
two peaks in pre-monsoon and one peak in post-monsoon season. However,
Puranik (1990) observed the presence of protozoea in March/April at station
located in the confluence of Nethravati-Gurupur estuary. Vikas (2004) observed
the protozoea in March/April at Sita-Swarna estuary, Udupi.
In the present study, zoea varied from 01 to 1640 No/m3 (Table 32). They
were present in all the months accept June/July and January at station 1
(confluence region). They were dominant in October month at station 2 in Haladi
estuary, it was not found in June/July of monsoon season. The abundance was
more in December month. At station 3, it was dominant in pre-monsoon and post-
monsoon season. It is only recorded in September month of monsoon season. The
maximum number was observed in May month of pre-monsoon season. At
station 4, in Chakra estuary they were not found in March/April and August
month. The numbers were more in September month of monsoon season. At
station 5, it was not found in April of pre-monsoon season and June/July and
August of monsoon season, but they were present in remaining months. From the
Figure 49, it becomes clear that the zoea larvae were abundant during post-
monsoon season to that of pre-monsoon and monsoon season. The spatial
distribution revealed the maximum density was occurred in Haladi estuary and
confluence region. The lower density was observed in Chakra estuary. Similar
seasonal trend was observed by Patil (1987), Puranik (1990), Ronald (2001) and
Vijay Kumar (2002) in Nethravati-Gurupur estuary and Vikas (2004) in Sita-
Swarna estuary respectively.
Achuthankutty (1987) documented the abundance of these larvae in
Mandovi-Zuari estuary. In the present study, zoea larvae were found to be
belonging to developmental stages of various types of crabs and shrimps. While
comparing the distribution of protozoea and zoea with the salinity variation, it is
evident that zoea preferred mixoeuhaline and polyhaline conditions, whereas
protozoea prefers only mixoeuhaline conditions.
In the present study, mysis larvae occurred sporadically with low numbers
and varied from 01 to 705 No/m3. The seasonal distribution revealed the presence
of moderate numbers in February/March in all stations of pre-monsoon season.
Whereas during monsoon season, mysis larvae were absent in July month in all
the station. The higher abundance was found in September month. In post-
monsoon season, they were occurred maximum number in November/December.
The seasonal variation of mysis larvae revealed that it was dominant in post-
monsoon season. The spatial distribution exhibit that mysis larvae were dominant
in Haladi estuary than that of confluence and Chakra estuary (Figure: 50). Few
number of mysis larvae without clear-cut seasonal variation were recorded by
Patil (1987), Ronald (2001), Vijay Kumar (2002) and Vikas (2004) in Nethravati-
Gurupur estuary and Sita-Swarna estuary respectively.
5.7.1.11. Molluscan larvae In the present investigation, molluscan larvae comprising of spats of
gastropods, bivalves and echinoderm larvae. The gastropod larvae varied from
133 to 1870 No/m3 (Table 33). The seasonal distribution of gastropod larvae
revealed greater abundance in March, September and October month, whereas
moderate to low numbers are present in February, April, July and November
(Figure: 51). The gastropod larvae exhibited dominant in all the seasons. The
spatial variation revealed that the station located at and near to the confluence
have more numbers than away from it.
The bivalve larvae consisted of spats of various clams and oysters. The
number of bivalve larvae varied from 133 to 2209 No/m3 (Table 34). The
seasonal distribution revealed greater abundance during monsoon season and
moderate numbers in March, April, May, September and October in almost all
stations. However, these larvae were not observed in February (station 2 and 5)
in pre-monsoon season and July in monsoon season (station 1). It is dominant in
September month except at station 5. In post-monsoon season, it is not found in
November (station 1) and November/ December (station 4) respectively. The
spatial variation revealed that the Haladi estuary and confluence dominant by
these larvae and moderate number in Chakra estuary (Figure: 52). It is
interesting to note that the larvae were present in monsoon season, when salinity
ranged between 0.21 and 23.56 ppt. The larvae were exhibited decreasing trend in
post-monsoon season, when salinity showed increasing trend.
The number of echinoderm larvae fluctuated between 02 to 801 No/m3
(Table 34). The spatial variation revealed the larvae were occured more in pre-
monsoon season and post-monsoon season (Figure: 53). The maximum number
was observed in May, September and January month. The echinoderm larvae
exhibit dominance in confluence region and Haladi estuary.
Achuthan Kutty et al. (1981) and Gajbhiye et al. (1981) observed
molluscan larvae during pre-monsoon and at the beginning of monsoon in Kajvi
and Narmada estuary respectively. Kumar (1984) recorded the abundance of
molluscan larvae during pre and post-monsoon season along the south west coast
of India. However, Habib and Rahaman (1987) documented the abundance of
molluscan larvae during monsoon season in Agnair estuary. Pattanaik and Sarma
(1997) observed sporadic occurrence of molluscan larvae in Rambha Bay, Chilka
lake. While good number of molluscan larvae were observed by Sujata and
Panigrahy (1999) in Bahuda estuary, Orissa.
In Nethravati-Gurupur estuary, Bhat (1979) recorded greater number of
these spats during late post-monsoon and early pre-monsoon. Similar observation
were made by Patil (1987), Puranik (1990), Ronald (2001) and Vijay Kumar
(2002) in the same estuary. The present observation by and large is in agreement
with the observation made by the above authors. Vikas (2004) recorded the
dominance of molluscan larvae in pre-monsoon season and moderate number in
post-monsoon season in Sita-Swarna estuary, Udupi.
5.7.1.12. Planktonic protochordates
In the present study, Oikopleura sp., doliolids and salpids were the sole
representative of planktonic protochordates (Table 35). Doliolids were present in
January (station 1) at confluence region and in May (station 2) in Haladi estuary
and were absent throughout the study period. Similarly, salpids were observed at
all stations in May (pre-monsoon) and lesser number in February/ December and
January (station 1) at confluence region. They were absent in most of the stations
during all the months in study period.
In the present study, Oikopleura sp. varied from 02 to 6681 No/m3 (Table
35). The abundance of Oikopleura sp. during pre-monsoon season was observed
in February at all the stations. This protochordate were absent in July month
throughout the study period except in station 1. The abundance of Oikopleura sp.
during monsoon season is different in different stations. The monsoon abundance
was noted in June month at station 1 and 2, September month at station 3 and in
August month in station 4 and 5. The post-monsoon peak was observed in
December/January at all the stations except at station 5. The maximum peak was
noted in November. From the Figure 54, it could be stated that this protochordates
exhibited a bimodal seasonal oscillation with peak in pre-monsoon and post-
monsoon. Pillai et al. (1975) recorded the occurrence of Oikopleura sp. from
November to April in Vembanad lake. Reddy (1977) and Eknath (1978)
encountered high numbers of Oikopleura sp. in the inshore waters of Mangalore.
Santanam et al. (1975) noted conspicuous difference in the period of occurrence
and abundance in the sea, estuarine, backwater and mangrove areas station along
the east coast. They recorded the two distinct peaks of abundance one in March
and other in October at the estuarine stations.
Sujatha and Panigrahy (1999) observed the abundance of Oikopleura sp.
during pre and post-monsoon season in Bahuda estuary, Orissa. The bimodal
oscillation in seasonal variation was documented by Bhat (1979), Nagarajaiah
(1980), Patil (1987), Puranik (1990) and Vijay Kumar (2002) in Nethravati-
Gurupur estuary in Dakshina Kannada and Vikas (2004) in Sita-Swarna estuary
respectively.
In the present study, the seasonal variation of this group is in conformity
with works carried out by above authors. The abundance of Oikopleura sp.
coincided with salinity range between highest 34.49 and lowest 0.21 ppt. The low
salinity prevailed at August month restricted the distribution in monsoon season.
Whereas at stations having salinity range between 30.05 and 11.12 ppt were
represented good number of Oikopleura sp. coinciding with the high and low
salinity regime. Similar observation was observed by Vijay Kumar (2002) in
Nethravati-Gurupur estuary and Vikas (2004) in Sita-Swarna estuary. However,
Patil (1987) and Puranik (1990) have observed greater abundance during high
saline regime (pre-monsoon).
5.7.1.13. Fish eggs and larvae
In the present study, the fish eggs were observed at all the stations during
most of the months except July. The number of fish eggs varied from 01 to 552
No/m3 (Table 36). Whereas fish larvae varied from 01 to 2762 No/m3 (Table 37).
The seasonal distribution of fish eggs revealed greater abundance in April/
May at all the stations (Figure: 55) except at station 4 and 5. The second peak was
observed in June (station 1, 2 and 3), September (station 4 and 5) and third peak
was in October (station 1 and 2) and November (station 2, 3 and 5). Therefore, it
could be stated that a clear-cut seasonal distribution could not be recognised. The
spatial distribution revealed greater frequency of occurrence at station 1, 2 and 3
compared to 4 and 5.
The examination of the fish eggs revealed the presence of different types
of eggs belonging to Carangidae, Engraulidae, Clupeidae and Scombridae. Among
them, Engraulidae dominated in September of monsoon season and Carangidae
dominant in pre-monsoon season. Whereas Engraulidae, Scombridae and
Clupeidae observed in post-monsoon season.
The seasonal distribution of fish larvae revealed greater frequency of
occurrence and abundance during post-monsoon season compared to pre-monsoon
and monsoon season (Figure: 56). During post-monsoon season, the fish larval
population consisted of Engraulidae, Scombridae, Clupeidae and Sillaginidae.
While in pre-monsoon season, fish larval population consisted of Carangidae and
Soleidae. The spatial distribution revealed greater number at the confluence. In
the pre-monsoon season, the maximum abundance was recorded in May month in
all the stations. Whereas in monsoon season, it is June (station 2 and 5), August
(station 1 and 3) and July (station 4) respectively. The post-monsoon peak was
noticed in November except station 2 (December).
Along east coast of India, Nagarajan et al. (1979) studied the fishes of
Vellar estuary in Porto Novo. Nammalwar et al. (1991) observed two peaks of
fish larvae during pre and post-monsoon season in Adyar estuary and Koralam
backwaters. Pattanaik and Sarma (1997) while working on the zooplankton
community of Rambha Bay, Chilka lake observed peak abundance of eggs and
larvae during March to September. Mishra and Panigrahy (1999) in Bahuda
estuary observed two peaks of fish eggs and larvae during November/December
and May/June. Along the coastal waters of Mangalore, Menon et al. (1977) and
Reddy (1982) recorded a good number of fish eggs and larvae during January to
April and October to December. However, Bhat (1979), Patil (1987), Puranik
(1990), Ronald (2001) and Vijay Kumar (2002) observed fairly good number of
fish larvae during post-monsoon and early pre-monsoon in Nethravati-Gurupur
estuary. Vikas (2004) documented the greater frequency of occurrence and
abundance of fish eggs in pre-monsoon season and fish larvae in post-monsoon
season at Sita-Swarna estuary. Padmavathi and Goswami (1996) while working
on zooplankton ecology in the Mandovi-Zuari estuarine system, documented
greater abundance of larvae during pre and post-monsoon season. While
comparing the distribution of fish larvae with that of salinity variation, it becomes
very clear that the larvae were more abundant, when the salinity was higher and
minimum during monsoon, when the salinity was extremely low. However, the
larvae present during monsoon season were found to be mostly belonging to
Clupeidae.
Among the various hydrographical parameters, the salinity of water was
found to exert greater influence on occurrence, abundance and distribution of
zooplankton. The relationship between total zooplankton and salinity revealed
greater abundance in mixoeuhaline condition during pre-monsoon season and
polyhauline condition during post-monsoon season. In the monsoon season, the
lesser abundance coincided with limentic condition due to south west monsoon
season. The spatial distribution revealed a greater abundance of zooplankton at
station 2 located in Haladi estuary and station 1 located in confluence region
during both pre and post-monsoon season (Figure: 63).
5.8. Macrobenthos
The qualitative and quantitative distribution of benthic organisms both in
space and time were carried out in the estuarine limbs of Haladi-Chakra estuarine
complex.
5.8.1. Qualitative composition During the present investigation different groups of benthic organisms
were recognised and they are belonging to class: Polychaeta, Crustacea, Mollusca
and along with other group of egg cases, sand tubes, annelida tube and fish. The
numerical abundance of these varied between stations and months.
The percentage contribution of polychaetes in the study period fluctuated
between 0.56 and 50.63% to the total benthos. Whereas crustaceans varied from
0.37 to 76.50%. The molluscans were dominanted throughout the period of study
and their percentage contribution to the total benthos varied from 13.89 to
97.62%. The percentage contribution of egg cases, sand tubes, annelida tube and
fish together varied from 0.0 to 34.66% to the total benthos (Table 38 to 42;
Figure: 57 to 59).
5.8.1.1. Polychaeta
During the study the species of polychaetes belongs to 7 different families
such as Nephtydae, Nereidae, Onuphidae, Glyceridae, Arenicola, Maladanidae
and Sabellaridae have been recorded. The percentage of polychaetes to the total
benthos ranged from 0.56 to 50.63%. It is evident that at station 1 located in
confluence registered higher number of Nereidae followed by Nephtydae and
Glyceridae. The percentage contribution of polychaetes to the total benthos at
confluence region varied from 0.56 to 8.42%. Whereas in the Haladi estuary
(station 2 and 3), the polychaete population was dominated by Nereidae,
Nephtydae followed by Maladanidae, Glyceridae and Arenicola. The percentage
contribution varied from 1.88 to 50.63%. Further, Nereidae at both the stations
were present almost throughout the study period. While others were not so
common and formed the bulk of the polychaete population. In Chakra estuary, the
contribution of polychaetes to the total benthos varied from 1.22 to 53.6%. At
station 4, Nereidae, Glyceridae and Nephtydae dominated the polychaete
population followed by Maladanidae. Whereas at station 5, the Nereidae
dominated in the polychaete population followed by Glyceridae and Nephtydae
located in chakra estuary. The other polychaetes belonging to Arenicola and
Sabellaridae were sporadically present with very low density in the study period.
The seasonal distribution of Polychaetes revealed greater abundance during the
monsoon season followed by pre-monsoon and post-monsoon season.
In the backwaters and estuaries of Cochin and Vembanad lake along the
west coast of India, Kurian et al. (1975), Kurian (1977), Pillai (1977), Ansari
(1977), Saraladevi and Venugopal (1989), Sunil Kumar (1995), Kumar, (1997),
Sunil Kumar, (2002a) and Sunil Kumar (2002b) observed the dominance of
polychaetes in the benthic community. Ramachandra et al. (1984) recorded higher
number of Dendronereis arborifera and Sabellaria cementarium in the polychaete
community of Mulki estuary, west coast of India.
Ansari et al. (1986) while working on the macrobenthos of Mandovi-Zuari
estuary observed 11 species of polychaetes of which Glycera alba was dominant.
Dominance of polychaetes in silty sand substratum was documented by Bhat and
Neelakantan (1988) in Kali estuary, Uttara Kannada.
Prabhu et al. (1993) observed 66 to 100% contribution of polychaetes to
the total benthos in the nearshore sediments off Gangoli, Dakshina Kannada.
Chakraborty and Choudhury (1997) observed six families of polychaetes with
Captellidae representing higher density and diversity in Hoogly estuary, West
Bengal. Sunil Kumar (2002a) in Cochin estuarine mangrove habitat observed 8
families of polychaetes with dominance of Nereidae, Eunicidae and Captellidae.
Along the east coast of India, the dominance of polychaetes both in species
and abundance at all the stations in the Vellar estuary was reported by Chandran et
al. (1982). Among the polychaetes, Nepthys sp., Polybranchia sp., Ancistrosyllis
sp., Lumbriconereis sp., Cossura sp., Glycera sp., Laonema sp. and Heteromastus
sp. were the common. Vijayakumar et al. (1991) while investigating on benthic
fauna of Kakinada Bay and backwaters recorded the dominance of polychaetes
with an average of 44.30%. While working on ecology of benthic macrofauna in
Cuddalore-Uppanar backwaters, Murugan and Ayyakkannu (1991) observed
higher contribution of polychaetes to the total macrobenthos and they have
identified 28 different species of polychaetes in the backwater system. The study
of Jagadeesan and Ayyakkannu (1992) revealed the dominance of polychaetes
followed by Crustacea in the Coleroon estuary and inshore waters of south east
coast of India and recognised more than 20 species of polychaetes and opined that
the bottom sediment and organic carbon were favorable for higher density of
fauna. Prabha Devi (1994) while studying on benthic fauna of Coleroon estuary
observed dominance of polychaetes in the benthic population, which formed
67.02% of the total fauna. The author reported 10 different species of polychaetes
with varying number in space and time. Chakraborty and Choudhury (1997)
identified 14 species of polychaetes belonging to 6 families and observed
variation of polychaetes in time and space.
In the present investigation, the seasonal distribution of polychaetes
revealed greater abundance during monsoon season followed by pre-monsoon
season and post-monsoon season. The spatial distribution indicated increased
abundance with increased distance from the confluence. While comparing the
abundance of polychaetes with that of the sediment texture, it becomes clear that
wherever the percentage of silt has increased in those stations and months
polychaete population exhibited a greater abundance, although sediment
dominated by sand throughout the period of study. The higher polychaetes
population coincided with increased silt percentage in the sediment. However,
Pillai (1977) observed greater contribution of polychaetes in sandy substratum
during the post-monsoon season. The spatial distribution indicated increased
abundance with increased distance from the confluence.
Similar relationship was observed by Chandran et al. (1982) in Vellar
estuary. Ramachandra et al. (1984) in Mulki estuary and Prabhu et al. (1993) in
the nearshore waters of Gangoli observed the dominance of polychaetes in sandy
substratum and clayey-silt substratum respectively. Sunil Kumar (2002a) observed
the relationship between sandy-silt substratums with greater abundance of
polychaetes in Cochin estuarine mangrove habitat. Nagendra Babu (2004) while
comparing the abundance of polychaetes with that of sediment texture, it becomes
clear that wherever the percentage of silt increased in those stations and months
the polychaetes dominants in Sita-Swarna estuary. Shiva Kumar (2005) observed
the abundance of polychaetes increased with percentage of silt with clay increased
in the sediments in Mulki-Pavanji estuary. In the present study, the observed
relationship between variation of polychaete population and sediment texture is in
agreement with the works of the above authors. However, Shanthanagouda (2001)
in Nethravati-Gurupur estuary could not observe any clear relationship between
polychaetes and type of sediment.
5.8.1.2. Crustacea In the present study, few individuals of crustaceans such as crabs,
juveniles of shrimps, barnacles and amphipods formed the bulk of the crustaceans.
The percentage variation of crustaceans to the total benthos varied from 0.37 to
76.50%. The class amphipods were represented family such as Gammaridae,
Caprellidae and Orechastredae. Whereas barnacles were represented by only one
species that is Balanus balanoid. In the present study, the crabs and shrimps
occurred less frequently with low to very low numbers (Table 45 to 49). It
becomes evident that the barnacles occurs more frequently than that of crabs and
shrimps. Barnacles in the present study occurs more frequently with greater
abundance. Most of the barnacles observed during the period were found settled
on small pebbles, shells of molluscs, leaves and twigs. The abundance of
barnacles in the benthic samples were observed by Bhat (1979), Ramachandra et
al. (1984), Sahoo (1985) and Shanthanagouda (2001) in Mulki and Nethravati
estuaries and Nagendra Babu (2004) in Sita-Swarna estuary respectively.
The percentage contribution of crustaceans to the total benthos at
confluence region varied from 0.44 to 6.15%. Among the crustaceans, Balanidae
(thoracica) was found to be dominated at station 1 followed by Caprellidae and
Orechastredae. In Haladi estuary, the percentage contribution of crustaceans
varied from 5.0 to 76.5%. Among the amphipods the Gammaridae and Caprellidae
occurred more frequently with higher numbers whereas, other classes were
present in lower numbers. However, Balanidae (thoracica) were observed in dead
form during pre-monsoon, monsoon and post-monsoon season and formed the
bulk of the crustaceans. In Chakra estuary, the contribution of crustaceans to the
total benthos varied from 0.37 to 62.98%. Balanidae (thoracica) and amphipoda
were observed more frequently and formed the bulk of the crustacean community.
The seasonal distribution of crustaceans revealed greater abundance of
families like Caprellidae, Gammaridae and Orechastredae of amphipoda and
Balanidae of thoracica during the monsoon season at confluence region. In post
and pre-monsoon season, these crustaceans were found in lesser numbers. Crabs
and shrimps were absent throughout the study period.
In Haladi estuary (station 2 and 3), amphipods along with barnacles were
present. At the later half of the monsoon with concomitant increase in salinity
higher numbers of Gammaridae, Caprellidae were formed the bulk of the
crustacean during monsoon season. During the post-monsoon season, the class
crustacean was represented by Gammaridae, Caprellidae and along with higher
dominance of barnacles. During pre-monsoon season, the class Gammaridae,
Caprellidae and Orechastredae along with barnacles formed the peaks with few
numbers of shrimps.
In Chakra estuary (station 4 and 5), Balanidae of thoracica and amphipods
(Gammaride/Caprellidae) formed the bulk of crustaceans during monsoon season.
During post-monsoon season, a prominent peak found to be constituted by
Balanidae of thoracica, Caprellidae, Gammaridae and Orechastredae of
amphipods along with few numbers of Squillidae of Stomatopoda and shrimps.
During pre-monsoon season, the class crustaceans were constituted of few
numbers of portunids of decapods, shrimps and large number of barnacles. The
amphipods such as Gammaridae, Caprellidae and Orechastredae formed the bulk
of crustaceans. The seasonal variation revealed that crustacean populations were
abundant in monsoon season followed by post and pre-monsoon season.
Ansari (1977) in Cochin backwater, Ansari et al. (1994) in Marmagoa
harbour, Goa recorded fairly good numbers of Gammaridae and Caprellidae in the
benthic samples. Prabha Devi (1994) observed common amphipods such as
Grandierella sp., Gileri sp. and Corophilum sp. in Coleroon estuary.
Further, the contribution of amphipods to the total bulk of crustaceans is
more than that of the other forms. The seasonal distribution of amphipods
revealed greater abundance during monsoon season followed by post-monsoon
and pre-monsoon season. It is interesting to note that during monsoon the
abundance of amphipods were responsible for bringing down the population of
polychaetes and gastropods. This relationship is more evident at stations in
Haladi estuary (station 2 and 3).
The spatial distribution revealed greater diversity of crustaceans in Chakra
estuary than that of Haladi estuary and confluence region. Ansari et al. (1986)
recognised significant contribution of crustacean to the total bulk of macrobenthos
in Mandovi-Zuari estuary, Goa. Along the east coast of India, Prabha Devi (1994)
observed fairly good numbers of amphipods in Coleroon estuary and documented
higher population in post-monsoon and lower during summer season. Ingole
(2002) recorded moderate number of amphipods in the coastal waters of Dhabhol,
west coast of India.
However, Prabhu et al. (1993), Gopalakrishnan and Nair (1998), Mohan
Kumar (1999) and Shanthanagouda (2001) could not observe significant
contribution of crustaceans in general and amphipods in particular to the total
macrobenthos in the Gangoli, Mangalore coastal waters and Nethravati-Gurupur
estuaries respectively. Nagendra Babu (2004) recorded the greater abundance of
Gammaridae and Caprellidae belonging to the class amphipods draw a significant
contribution to crustaceans, which ranged from 0.0 to 66.25% to the total macro
benthos in the Sita-Swarna estuary, Udupi. Shiva Kumar (2005) while studying on
macrobenthos observed the crustaceans percentage of 0.0 to 75.76% with
dominance of amphipods was represented by Ampithoidae, Corophiidae,
Caperillidae, Gammaridae and Hyalidae in Mulki-Pavanje estuary, Dakshina
Kannada.
5.8.1.3. Mollusca
In the present investigation, the Phylum Mollusca was represented by class
Gastropoda, Bivalvia, and Scaphopoda. In both Haladi and Chakra estuary,
molluscs were dominant in the total macrobenthic population throughout the
period of study. The percentage variation of molluscs during the study period
varied from 13.89 to 97.62%. Ansari (1977) observed the dominance of molluscs
in the Cochin backwaters. Studies of Ramachandra et al. (1984) in Mulki estuary
revealed the greater contribution of molluscs to the bulk of macrofauna. The
dominance of molluscs in the coastal waters of Mangalore was observed by
Devassy et al. (1987) and Gopalakrishnan and Nair (1998). Nagendra Babu
(2004) recorded the 12.5 to 100% of molluscs population dominating the total
macrobenthic population through out the study period in Sita-Swarna estuary.
Shiva Kumar (2005) observed the variation of molluscs to the total macrobenthos
contributed in the range of 2.27 to 94.44% in the Mulki Pavanje estuary, Dakshina
Kannada.
During the study period, the percentage contribution of molluscs to the
total benthos varied from 43.50 to 97.62% at the confluence (station 1). Among
the Phylum Mollusca, Bivalvia was more abundant followed by Gastropoda and
Scaphopoda. The Scaphopoda was represented by Dentallium. The percentage
contribution of molluscs in the Haladi estuary (station 2 and 3) varied from 13.89
to 67.29%. The percentage of gastropods was lesser than bivalves. While
Scaphopoda was reported in the month of April/May. Among the Gastropoda;
Littorinidae was abundant followed by Telescopium to the total benthos followed
by Cerithidae. Among the bivalves the percentage contribution of Meretrix sp. and
Katalysia sp. followed by Donacidae was found to be more dominated. While in
Chakra estuary (station 4 and 5), the percentage of molluscs values ranged
between 19.6 to 92.10%. The percentage contribution of gastropods was more
than bivalves. While Scaphopoda were recorded in sporadic numbers throughout
the study period. Therefore, it becomes clear that the confluence estuary supports
higher density of molluscs than that of Chakra and the Haladi estuary.
Ramachandra et al. (1984), Gopalakrishna and Nair (1998), Mohan Kumar
(1999), Shanthanagouda (2001) could not observed clear cut spatial variation of
molluscs in the coastal waters of Mangalore and Nethravati-Gurupur estuary
respectively. However, Harkantra and Parulekar (1981) in the coastal zone of Goa,
Divakaran et al. (1981) in the inshore water of Vizhinjam, Murugan and
Ayyakkannu (1991) in Cuddalore-Uppanaru backwaters and Prabha Devi (1994)
in Coleroon estuary did not observe the dominance of molluscs.
The seasonal distribution of molluscs at the confluence region revealed the
dominance of Umbonidae, Cerithidae, Turritellidae, and Conidae followed by
Olividae of the class Gastropoda. Littorinidae and Babilonia occurred in lesser
numbers. Whereas the bulk of the Bivalvia was mainly contributed by Arcidae,
Donacidae, Katalysia sp., Meretrix sp. and Perna sp. of the family Mytilidae. In
addition, Dentalidae also contributed to the bulk of the molluscan population.
During pre-monsoon season, Conidae, Umbonidae, Turritellidae and Telescopium
were abundant followed by Olividae sp., Littorinidae sp. and Babilonia sp.
Whereas the class Bivalvia was represented by Donacidae, Arcidae and spats in
large numbers along with Katalysia sp. of the family Mytilidae, thus forming the
bulk of Bivalvia. Dentallidae were present throughout the season with higher
number in pre-monsoon. During post-monsoon season, Umbonidae, Turritellidae,
Conidae and Telescopium with Cerithidae formed the bulk of gastropods followed
by Trochidae and Olividae, Archidae, Meretrix sp. and Donacidae mainly
contributed the bivalve population. The abundance and diversity of bivalves
during monsoon season is more than that of gastropods. Whereas the higher
abundance and diversity of gastropods than that of bivalves were observed during
pre and post-monsoon season. However, Dentallidae were present in large
numbers in pre and post-monsoon season. The total population of molluscs
reported to be high in February of pre-monsoon season.
In Haladi estuary at station 2, the Littorinidae formed the bulk of
gastropod population followed by Telescopium and Cerithidae. Whereas, Meretrix
sp. constituted Bivalvia. Dentallidae were reported in lesser numbers throughout
all the season. At station 3, Littorinidae of gastropods and Meretrix sp. of bivalves
were found to be abundant. Dentillidae was recorded in April/May. The species
diversity and abundance of Bivalvia is higher than gastropods. Again the total
populations of Mollusca were more in pre-monsoon season followed by the post-
monsoon and monsoon season.
In Chakra estuary (station 4 and 5), the dominance of Littorinidae,
Cerithidae followed by Telescopium of the class Gastropoda was observed. The
bivalve population consisted of katlaysia sp. of family Mytilidae followed by
Meretrix sp. Dentillidae was observed in megere numbers throughout the study
period. In post-monsoon season, the population of gastropods dominated by
Cerithidae, Turritellidae and Littorinidae. The dominance of Katlaysia sp. and
Meritrix sp. of Mytilidae was observed in the bivalve population.
In pre-monsoon season, Littorinidae and Cerithidae formed the bulk of
gastropods. While Katalysia sp. and Meretrix sp. of Mytilidae contributed to the
bulk of bivalve population. The population of Bivalvia is more than that of
gastropods in monsoon season. Whereas during post and pre-monsoon season, the
diversity of bivalves was found to be more than that of gastropods.
The seasonal distribution of molluscs in the present study revealed the
presence of high numbers during post-monsoon season followed by pre-monsoon
season. The lower numbers during monsoon season.
The spatial distribution revealed the greater numbers or diversity of
molluscs dominated in the confluence region followed by Chakra and Haladi
estuaries. So this variation was found to be due to higher percentage of sand in
sediment at confluence region followed by Chakra and Haladi estuary. In addition,
proximity to the sea and transportation of forms in to the estuarine basin could
also be the factor responsible for high population of molluscs in confluence and
Chakra estuary.
Harkantra (1975) documented the abundance of Meritrix casta from
January to July and low numbers during peak monsoon in Kali estuary.
Ramachandra et al. (1984) documented low number of molluscs during monsoon
and high population during post and pre-monsoon season in Mulki estuary.
Devassy et al. (1987) and Gopalakrishnan and Nair (1998) and Mohan Kumar
(1999) observed the peak abundance of molluscs during post-monsoon season.
Shantanagouda (2001) could not observe clear spatial variation of molluscs in the
coastal waters of Mangalore and Nethravati-Gurupur estuary respectively.
Nagendra Babu (2004) and Shiva Kumar (2005) observed the dominance of
mollusca in post and pre-monsoon season through out the study period in Sita-
Swarna estuary and Mulki-Pavanje estuary along the west coast of India.
5.8.1.4. Others
Sand tubes, egg cases, dead annelids tubes, and fishes formed the
bulk of miscellaneous forms. The percentage contribution of this group
varied from 0.0 to 34.66%. The seasonal distribution revealed the
greater numbers or diversity of miscellaneous forms dominant in the
Chakra estuary than that of Haladi estuary and confluence region
No fish was reported at confluence throughout the study period.
Whereas, egg cases dominant in monsoon season and sand tubes
occurred frequently in sporadic numbers throughout the study period.
The percentage contribution of this group varied from 0.84 to 30.4%.
In confluence, the abundance of egg cases was found to be more than
sand tubes and dead annelids tubes.
In Haladi estuary (station 2 and 3), the contribution of egg cases, sand
tubes, fish and annelida tubes were varied from 0.52 to 28.79% found to be higher
in pre and post-monsoon season, compared to monsoon season. The egg cases and
sand tubes were dominated in this group.
In Chakra estuary (station 4 and 5), sand tubes were common during pre
and post-monsoon season and found lesser numbers in monsoon season. While
egg cases and annelida were found to be higher in monsoon season followed by
pre and post-monsoon season. Fish was reported in pre-monsoon season. The
contribution of this group varied from 0.43 to 34.66%.
The seasonal variation of miscellaneous group revealed greater abundance
in pre-monsoon, monsoon season and followed by post-monsoon season.
Neelakantan et al. (1988) observed juveniles of eels in the benthic samples
collected from Kali estuary. Frequent occurrence of egg cases and sand tubes in
the Nethravati-Gurupur estuary was observed by Shanthanagouda (2001).
However, he could not observe any fishes in the benthos of same estuary.
Nagendra Babu (2004) observed the fish belonging to Engralidae were present in
the benthos collected during monsoon season at Sita-Swarna estuary, udupi.
Shiva Kumar (2005) reported the Hydroidae, sand tubes, mud tubes and egg cases
formed the bulk of miscellaneous forms. They were dominated in pre and post-
monsoon season.
The total percentage of polychaetes and miscellaneous forms contribution
to the macrobenthos in the present study were more at station 2 in Haladi estuary
with the maximum of 29.52418% and 34.91716% respectively. The greater
percentage of total crustaceans was observed in station 3, attening maximum of
38.51061%. Whereas the total percentage of molluscans was higher in station 1 at
confluence registering 28.37877%. From the Figure 64 and 65, it is evident that
the greater percentage of total polycheates, miscellaneous forms, crustaceans and
molluscans were dominant in stations at Haladi estuary and confluence region
respectively. The percentage of total crustaceans dominant the total macrobenthos
in the present investigation.