zonation on a tropical sandy shore

Zonation on a Tropical Sandy ShoreAuthor(s): F. C. VohraSource: Journal of Animal Ecology, Vol. 40, No. 3 (Oct., 1971), pp. 679-708Published by: British Ecological SocietyStable URL: http://www.jstor.org/stable/3445 .

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679

ZONATION ON A TROPICAL SANDY SHORE

By F. C. VOHRA

Division of Ecology, School of Biological Sciences, University of Malaya, Kuala Lumpur, Malaysia

INTRODUCTION

Purchon & Enoch (1954) have described the zonation of the marine fauna and flora on a rocky shore near Singapore. Relating this zonation to tidal data, they revealed a pattern broadly similar to that established by workers in temperate regions (Stephenson 1953; Stephenson & Stephenson 1949, 1950, 1952, 1954). Further, they have shown that Singapore shores appear to have 5-20%y longer coverage by the sea than do most British coasts and they claim that this may enable some species to occur at levels at which they might otherwise be unable to survive. Berry (1964) and Lee (1966) have described the natural history of organisms on shores of North Penang and on shores off Tanjong Tertip on the south-western coast of Singapore respectively.

The present work on the sheltered sandy shore of Singapore examines the zonation of the common macrofauna and the various environmental factors affecting the distribution of this fauna and compares this tropical sandy shore with sandy shores at other latitudes.

THE SITE OF INVESTIGATION (MATA IKAN)

Kampong Mata Ikan is a small fishing village on the east coast of Singapore (Figs. 1 and 2). Its shore is typical of almost all areas around eastern Singapore Island. Other places are muddier and often bear mangrove vegetation, particularly on the western side. The area was selected as being more nearly a pure sand beach, less subject to human inter- ference than are other beaches in the area, and easy of access. It is washed by the Singa- pore Straits, which is a narrow stretch of water, separating Singapore from the southern tip of Malaya on the one hand and from the Rhio Archipelago on the other.

The shore slopes steeply from the upper landward limit, marked by some sparsely growing grass, coconut palms and casuarina trees, to a larger zone of gradual gradient. Then follows a seaward zone of Enhalus acoroides Rich. ex. Steud. Slightly beyond extreme low water of spring tides, there is a series of 'kelongs' or fishing stakes.

The consistency of the soil for about 600 ft (270 m) seaward of the landward limit is fairly constant. This area is well drained except for some small pools and furrows at low tides but over a further zone of about 200 ft (60 m) the soil is soft and sticky and supports an angiosperm Halophila ovalis Hooker f. From here to the extreme low water of spring tide and even lower, the soil is very soft and perpetually waterlogged. This is characterized by the flowering plants, Enhalus acoroides and Cymodocea rotundata Aschers and Schweinf., which provide support and shelter for a great number of animals. Vertical section of the soil showed a top yellowishbrown layer (0 5-5 cm thick) coveringjblacksand. Varying amounts of Ulva reticulata Forskal and vegetable residue at different stages of decay were always present on the beach. The former is brought by the incoming tide and is generally left heaped up at the high tide mark by the receding tide.



680 Zonation on a tropical sandy shore

1O3c4d 1030 45' 103?5o' 103i55' 104

JO HORE

KRANJI SELETAR 0

10 1

CHANGI

i PEPIERCE RESERVOIR

-Ix 5~~~~~~~~. Mota Ikon It15j9 > Mc RITCHIE RESERVOIRTA

10 S. 5. Bedok IKAN 10 2 0 \ UNIV./ 5 - nJ 20'

OF SINGAPORE BEDOK

STAIT

SIN G A PORE

SP.LAKANG, -- 012 345 1 -

_ <7 MATI Miles i5' I I ~ ~ ~ ~ ~~I I

103?40o 103?45' 103!501 103055' 1040

Fso. 1. Map of Singapore Island with site of investigation, Mata Ikan.

24 25 26 27

7,-

K';.- ~~~~~~~~~~~~AYER-

0 4 "- 1 GEUU

SOIMAPA , N "

CHANGI:-;-<- -4 * ILLAGEg>

I'~~~~~A

* ATAIKAN. VILLAG3E

'x, 01Q~Q KG PDN

FGMENGKWANG

? +~~~~~

Miles

O 2

FIG. 2. Large scale map of Mata Ikan area. 'T' marks the shore traverse along which collecting stations were located. The dotted area represents shore exposed by extreme low

tide.



F. C. VOHRA 681

A small stream, Sungei Mata Ikan, flows on to the beach between the transect line and the village jetty. At its mouth it divides into small runnels some of which run across the transect at different levels. The fresh water outflow of the stream is small except during heavy rains when it swells, changes its course and shifts soil over the shore. It also brings down to the beach some organic matter which provides an additional source of food for animals on the affected parts.

Stations Station 0 was situated above extreme high water spring tide mark where soil surface

temperature reached 500 C on sunny days. It was characterized by loose dry sand with sparsely growing grass. Except for a few common insects (e.g. ants, flies and grasshoppers) there was no typical fauna. No samples were taken at this station.

Station IA, located at a tidal height of 8&4 ft (2-6 m) on the steep slope A (Fig. 3), had maximum surface temperature of 44G C. Almost every high tide wetted part of this slope. The uniformly coloured substratum of clean sand became almost dry at low tide.

Station 1, height 5-8 ft (1-8 m), maximum surface temperature 400 C, generally well drained but waterlogged from May to September 1958. Abundant vegetable debris at places.

12 -Stn.O E

HWS.T M S L. L.W. NT 8 SLOPE A

6 t 6-Stn.2 Stn.3 Stn.4 Stn.5 Stn.6

O 4 _-| Enho/us zone

I 2 - _LWS.T.

50 100 200 300 400 500 600 700 800 900 1000 1100

Distance (ft)

FIG. 3. Profile of the Mata Ikan shore along the transect line. The vertical scale is exaggerated twenty-five times. Stations 1-6 are indicated. H.W.S.T., High water spring tide; H.W.N.T., high water neap tide; M.S.L., mean sea level; L.W.N.T., low water neap tide; L.W.S.T.,

low water spring tide.

Station 2, height 5 ft (IF5 m), maximum temperature 34-360 C; generally well drained and firm but with occasional small pools or a gully of water after rain; vegetable debris in considerable amounts.

Station 3, height 4-5 ft (14 m), maximum temperature 32-35? C; well drained except during rains, clayey deposits at a depth of about 3 in. at places.

Station 4, height 3-7 ft (1 1 m), resembled station 3 in other respects. Station 5, height 2-96 ft (0 9 m), maximum temperature 30-33? C. Soil soft and sticky

in general; a few firmer elevated patches with good drainage. Little vegetable debris but more shell gravel.

Station 6, height 2-25 ft (0 7 m), otherwise like station 5.

METHODS AND TECHNIQUES

A transect line was set out across the shore and the stations were located on this as shown




in Fig. 3. To compare tidal data at Mata Ikan shore with Tide Table predictions (1957- 58) direct observations of tidal movements were made on a calibrated pole erected alongside a 'Kelong' on 22 April 1958 when a tidal range of 0 7 ft (0-2 m) at 06.28 hours to 7-8 ft (2.5 m) at 13.00 hours (Singapore standard time) was predicted (Fig. 4). Slight wave motion was minimized by using a long 4 cm bore glass tube held vertically alongside the pole. Times and tidal levels on the pole were also recorded when the advancing sea edge reached each station on the transect line, this being signalled by a second observer on the shore. By use of the tidal heights of stations obtained in this way a shore profile was drawn (Fig. 3). A 15-day cycle (7-22 April 1958) approximating to the average conditions for the year (Colman 1933) was selected from the Tide Table predictions (Fig. 5).

ft Ir H.W.E.S.T.

10

9 H.WS.T:

8 _ .0000.0"60

7 _NT./ /H.NT

6 / Stn. I

5 M.S.L. Stn.2

// _Stn.3 4 -

/LN: - Stn.4

3 _ / _ Stn.5

2 / -Sta6

LW S.T; 0~

LWE.S.T

6a.m. 7 8 9 10 If 12 1p.m. 2 Time

FIG. 4. Graphical representation of tidal movements at Mata Ikan on the risilng tide of 22 April 1958. Zero on the vertical scale represents the estimated level of chart datum. The tidal heights of sampling stations are indicated. The following were obtained from Tide Tables: H.W.E.S.T., High water of extreme spring tide; H.W.S.T., high water of spring tide; H.W.N.T., high water of neap tide; M.S.L., mean sea level; L.W.N.T., low water of neap tide; L.W.S.T., low water of spring tide; L.W.E.S.T., low water of extreme spring tide.

Monthly faunistic samples were obtained from the collecting stations (1-6) by search- ing constant volumes of soils taken by a specially constructed sampler, +- x Ijm x 5 cm of 3 mm thick aluminium sheet (Fig. 6).

In a preliminary survey two groups of samples, 5 cm and 10 cm deep respecti'vely were examined. Deeper diggings were also made at various stations. The results were not appreciably different at various depths and thus it was decided, as did Watkin (1942), to ignore the deeper samples in the subsequent study, for the sake of efficiency and speed of sampling.



F. C. VOHRA 683

Two samples, one on either side of the transect, were taken on all occasions but the results were combined into one for analysis. The position of each sample core taken was determined by throwing the sampler blindly with eyes shut to disorientate the collector. The sampler was then pressed into the soil until halted by the flanges and wooden lid. After digging a small trench on three of its sides, a copper plate was passed with a sawing motion under the sampler. The plate with the sampler and soil was then lifted and turned over. The contained soil in the sampler was levelled against its sides before being trans- ferred into a labelled bucket for transport to the laboratory. This was considered to give uniform results, comparing favourably with those of earlier workers (Stephen 1929; Pirrie, Bruce & Moore 1932).

In the laboratory each sample was spread out evenly in four to five shallow enamelled trays (25 x 35 cm) with some sea water on the surface. These were covered with glass

-;z 8 - ~~~~~~~~~~~~~~~~~~~~~~~~~~Stn IA

6 - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Sin. I Stn.3Sf2

. ..Stn.. .220 2 d X Stfl*tn.6 P

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 April

FIG. 5. Graphical representation of tidal movements predicted for Singapore Inner Harbour for a period of 15 days (7-22 April 1958). Zero on the vertical scale represents the level of

chart datum.

3m

< ; T c m~~~~~~~c

FIG. 6. An aluminium sampler with wooden top for collecting faunal samples of I x i m x 5 cm each.

sheets and left overnight. Each tray was then examined and all visible living animals were separated. Thus most of the snails, bivalves, hermit crabs and some worms were collected.

A set of three sieves (5, 1b5 and 1 mm mesh respectively) were used (Brady 1943) and a 'souping' technique as used by Spooner & Moore (1940) and Holme (1949) was adopted while sieving. On the top sieve were retained vegetable matter, large polychaetes and bivalves, etc. while the middle sieve contained most of the polychaetes, small bivalves and hermit crabs which had left their shells. Smallest polychaetes, small crabs and nemertines, etc. were found on the bottom sieve.

All animals were suitably preserved after preliminary identification and counts. The number of damaged polychaetes was recorded by counting only heads.




Soil samples were collected at low tide by pushing a 3-75 cm diameter open tube into the soil up to a marked depth of 5 cm. The contained core of the soil was then cut off, corked and brought to the laboratory for analysis.

Soil analysis was conducted according to the methods of Beanland (1940), Watkin (1942), Holme (1949, 1953), Southward (1953) and Sanders (1956).

The soil particle size was based on the international scheme, except that 2-057 mm and 0211 mm mesh sieves were substituted for 2 mm and 020 mm sieves, respectively. Silt and clay in a sample were determined by pipetting representative fractions at 10 cm depth from the suspension in the cylinder after it had stood for 5 min and 8 h respectively. Other fractions were obtained by sieving through Endecottes test sieves. Results were ex- pressed as percentages of the parent oven dry sample (Table 1).

Surface water samples were collected with a teat-ended pipette from the sea edge at various stages of the tide while interstitial water samples were obtained by Smith's (1955) method. The turbid suspension was kept in a hard glass stoppered bottle to mini- mize pH changes. As far as possible samples were taken from well-drained areas. When such areas were rare, as at stations 5 and 6, small trenches were dug all round the spot to drain off the surface water before taking a sample. Prior to analysis, samples were filtered through a fine hard filter paper (Whatman No. 4).

Salinity determinations were made in the field using Harvey's method (1945) of titra- tion with silver nitrate, with necessary correction from Knudsen's tables (1901).

Field tests of pH were made within 20-30 min of collection, using bromothymol blue or cresol red, with appropriate salt error corrections (Buch & Nynas 1939).

Soil temperatures were recorded at surface, 5 cm and 10 cm depth respectively. Surface water temperatures were also taken.

ENVIRONMENTAL FACTORS

General climate Owing to its proximity to the equator, the island's climate is characterized by uniform

temperatures, high humidity and considerable rainfall (Tham 1953). Normally, there are very few days with constant bright sunshine or torrential rain throughout, the weather conditions varying from hot sun to an overcast sky with an occasional drizzle or rain. Weather data for the period of study (September 1957-September 1958) discussed later were made available by Changi R.A.F. Station. This is situated very close to Mata Ikan (Fig. 1), so there is every reason to believe that the two localities are climatically similar, though other Singapore areas may differ widely.

Rainfall and hours of sunshine The rainfall at Singapore is influenced by the south-west (May-September) and north-

east (November-March) monsoons. There are no well-marked dry and wet seasons, but the latter brings in more rain than the former. Thus May, June and July are normally the least wet months with an average rainfall of about 7 in. (178 mm) per month. This average increases steadily in the following months until a maximum of about 10 in. (254 mm) per month is reached for November, December and January (based on average for 52 years; Fig. 7a).

During the period of study December 1957 was wetter than its average with 15-8 in. (401 mm) of rainfall. July (1957) and September (1958) were driest with only 1-8 and 0-6 in. (46 and 15 mm) of rainfall respectively (Fig. 7b). Comparison of rainfall during



Table 1. Analysis of the soil from various stations at Mata Ikan (based on an average of three samples in each case); the maximum number of species collected at each station is indicated

Water Dissolved Total contents contents Coarse Medium Fine no. of IT1

calculated Organic and Stone sand sand sand Silt Clay species Stations separately content calcium > 2057 p 500-2057 , 211-500 p 20-211 p 2-20 It <2 p Total collected

la 647 0 16 0-86 2-11 26-11 68-82 2-23 0-2 0-2 100-69 1 20-5 2'98 1-63 28-68 43*46 14-53 4-0 3-01 2-3 100-59 45 2 21-32 1-4 1*8 18*58 42*98 22-21 4-78 3-23 5-58 100-56 51 > 3 18-85 1.55 1.5 11-03 57*10 21-34 3-93 1-55 2-8 100-80 58 4 20-08 1*59 1*71 12-5 47-49 26-43 6&22 1-96 2-9 100-80 62 5 19-5 1.5 1-82 10-69 40.3 32-44 8-42 1-12 4-35 100-64 70 6 20-92 1P62 4*08 7-84 43*12 32-05 9-07 1-32 2-25 101-35 71

00 ,(-




September 1957 (9 95 in. (253 mm)) and September 1958 (0-6 in. (15 mm)) indicates the degree of irregularity from year to year.

The average daily number of hours of sunshine varied from 2-9 in December to 7-4 in July during the period of study (Fig. 8).

Temperatures The monthly average maximum air temperature varied from 29 1 C in December

(wettest month) to 33 2? C in April and the monthly average minimum air temperature

12 (a)

10 _ C

12 ~ ~ ~ ~ ~ ~ ~ ~~~~2

I0~~~

0~~~~~~~~~~~~~~~~~~~~~~0

S O N D ~J F M A M J J A S

1.2 -I-- ~ 60 E

8~ ~ ~Setme 1958

0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~0

0 -R~~'

50? C.~~~~~~~~~~~~~~~~~~~

2~ ~ ~ ~ ~~~~~~~~2

26

S0 N 0 J F M A M J J A S

FiG. 7(a) Average rainfall of Singapore (in./month) based on 52 years. (b) Monthly mean air temperature myand rainfall ( ) at R.A.F. station Changi from September 1957 to

September 1958.

from 2395 C (December) to 2533 C (April), thus giving an average maximum range of 9.70 C through the period of study (Fig. 7b). The average monthly range between the maximum and minimum daily air temperatures, however, varied from 5-6' C in December to 8-2' C in March.

The surface temperature of the loose sand on the steep slope can vary from 25' C to 5O0 C.

On a hot day (7 July 1958) the surface temperature may vary from 260 C to 400 C on the upper shore (Stations 1 and 2) and from 290 C to 340 C on the lower shore (Stations 5 and 6) in continuous full sun (Fig. 9). An average day, on the other hand, with fewer



F. C. VOHRA 687

8 -

7 -

6

o4 I

3_

2 -

L I I I I I I I I I I

S O N D J F M A M J J A S

FIG. 8. Average number of hours of sunshine/day in each month in Singapore, September 1957-September 1958.

38-

36

34 I -

32 - - - /

30 /

Stn I . Stn2 5 . Stn 3 28 I LLLLL.r LLLL15 1,

36 36

34 I

32//

30

28 ~~~Stn 4 Stn 5 Smn. 6

715 815 915 05115 715 815 915 1015 M11 "

-15 815ei 945 1045 1115"'~ 0

FIG. 9. Soil temperature variations at various stations on the Mata Ikan shore throughout the period of tidal exposure on a hot sunny day-7 July 1958. -, Soil surface; - - -,

soil, 5 cm depth; , soil, 10 cm depth.




hours of sunshine, occasional drizzle and breeze (e.g. 15 June 1958) showed a range of about 5-6? C (from 28? C to 33? C) at the upper shore and of 3-4? C at the lower shore (Fig. 10).

At a depth of 5 cm the temperature on the steep slope rose to at least 360 C on hot days. On the upper part of the flat (Stations 1 and 2) the range was from 28? C to 36? C while on the lower flat (Stations 5 and 6) it was from 29? C to 33? C on a hot day. At 10 cm depth, the temperature variation was much less.

On an average day the 5 and 10 cm depth temperatures varied from 28? C to 32.5? C at stations 1-4.

34 -

32 -

30 Stn I

28

34 -

z.- 32-

30- pe 3 Stn. 2

928

34 -

32 -

30 _

_Stn.3 ,<:r aier 2 8

I I I 1 I I 5.30 6.30 7.30 8.30 12.30 13.30 14.30 15.30 16.30 1730

Time

FIG. 10. Soil temperature ranges at Mata Ikan beach on an average day, e.g. 15 June 1958. Since the lowest stations were exposed for a short while only, their temperature ranges are not included in the figure. , Soil surface; - . - . -, soil 5 cm depth; ---soil, 10 cm depth.

Tham (1953) and Wickstead (1958) showed that the range of sea temperature in Singa- pore Straits was between 26.5? C and 305? C. The general pattern followed that of the atmosphere, both being dependent on rainfall and sunshine. Surface water temperature at sea edge during monthly collections varied between 28? C and 32? C generally but on 22 April 1958, it was as high as 380 C near station 1.

Salinity Interstitial salinities at different stations under varied conditions of weather, exposure

and tide did not differ greatly from one another, the range being from 27 1%o to 31 6%o only. Because of rain, salinities of the coastal and interstitial waters remain fairly low.



F. C. VOHRA 689

High relative humidity and cloud cover limit evaporation and provide a check against appreciable rise in salinity. Thus salinities of samples collected from each station at low tide at 6.00 am and just before their respective coverage varied within 1%o only. Again, salinities of samples, collected from stations 1, 2, 3, 4, 5 and 6 after their exposure to bright sun for 73, 7, 6, 5, 4 and 2i h respectively, were very slightly higher than those of samples collected after rain on an average day.

Due to freshwater seepage at the upper stations and the proximity to the sea of the lower ones, the salinity is usually slightly higher downshore than upshore.

Depending upon tidal conditions, freshwater seepage or flow and rain, etc. on the shore, surface water salinity varied from 7T0%O to 31A4%,.

Straits water varied from 28 74%, to 31 ?8%, during the period 1948-49 (Tham 1953) and from 30O5%0 to 32-2%o for the period 1954-55 (Wickstead 1958). In both periods, the salinity pattern showed two maxima per year (March-May and October-November) and two minima (July-August and December-January). In the opinion of Robinson, Tong & Tham (1952) and Tham (1953) the two maxima seem to be caused by the inflow of high salinity water from the South China Sea, and the July-August minimum by the inflow of low-salinity water from the Java Sea and possibly the Malacca Straits during the south-west monsoon. The December-January minimum, however, is the result of heavy rainfall during the north-east monsoon.

pH This was determined occasionally (Table 2). In all cases lower stations showed higher

values than the upper ones. Excess of decaying vegetable matter at Stations 1 and 2 presumably tends to reduce the pH values at these places.

Table 2. pH values of the interstitial water collected from the sampling stations at Mata Ikan

Dates

25 Nov. 22 Jan. 23 April 27 July 30 Oct. April

Station 1957 1958 1958 1958 1958 1959

1 6-6 6-4 6 5 6-8 7-1 7-1 2 6-5 6-4 65 6-7 7-4 7-2 3 7 0 7-2 7 0 7-1 7-4 7-2 4 7.4 7-2 7.3 7-2 7-6 7.5 5 7.5 7.5 7.4 7.5 7-6 75 6 7-6 7-5 7-4 7-6 7.6 7.5

Tides In Singapore Straits tides show a transition from a semi-diurnal form at springs to an

almost diurnal type at neaps. The graph of tidal movements (Fig. 4) at Mata Ikan on 22 April 1958 showed a range

similar to that of Singapore Inner Harbour (Tide Tables, 1958) being 7-25 ft (2-2 m). against 7-1 ft (2-1 m). From the Tide Tables for Singapore Inner Harbour (1957, 1958) it is thus noted that during spring tides only one very low tide occurs per day. From April to September, this tide occurs early in the morning and from October to March in the evening. Hence, the lowest levels of the beach are never exposed to the greatest heat of the tropical sun.




Percentage emersion This varied from 9XYO at station 6 to 950 Y at station 1A (Fig. 11). The highest collecting

station (station 1) had an emersion time of 630.. The difference in time between coverage of station 6 and station 1 was 2 h, the tidal height difference being 3f42 ft (1P0 m).

Soil texture The results at the collecting stations along the traverse indicated a predominance

(82-90%) of coarser soil grades (>211 u). Medium (211-500 Iu) and fine (20-211 ,I) sands were least at station 1 and increased as the stone fraction decreased downshore towards station 6 (Table 1), but the variations were small and the overall composition relatively uniform.

Dissolved inorganic matter including calcium increases seaward. Freshwater seepage at the upper shore probably washes out this material from there.

9 _

-Jstn. IA. 8_/

7-

6- 6 Stn. I

5 - Stn.2

Stn.3

I4--t,, Stn.4

3 _ Stn.5

Stn.6 2 -

0 L _ I I I l l I 0 10 20 30 40 50 60 70 80 90 100

% exposure

FIG. 11. Percentage tidal exposure time along the Mata Ikan shore transect.

Except for station 1, where drift material accumulated, the amount of organic matter increased downshore towards station 6, though only very slightly. Because of small amounts of silt and clay, and the effect of the stream at various levels of the beach, no definite relationship can be ascertained between these fractions and tidal levels.

Wave action and turbidity During the change-over periods between monsoons (April-May and October-Novem-

ber), wind force is decreased and the sea as well as the weather is periodically calm. During monsoons, wind force increases (maximum in July-August), the sea is disturbed and the turbidity is high. Due to the protected nature of the shore and the presence of the seaward Enhalus zone, the effect of waves on the beach is much reduced. The inflow from the stream during rains increases the turbidity of the shore water and results in deeper runlets being, formed.



F. C. VOHRA 691

Table 3. Total number of species and individuals collected at each sampling station from September 1957 to September 1958; regions of maximum density for most abundant and

common species are in bold type

Stations

Species 1 2 3 4 5 6 Total

Bivalves 1. Anomalocardia squamosa (Linnaeus) 1 1 8 26 77 108 221 B 2. Arca auriculata Lamarck - - - - 1 2 3 B 3. Crassatellites radiata (Sowerby) - - - 1 - - 1 B 4. Cyclinella sinensis (Gmelin) - - - - 1 5 6 B 5. Donax faba Chemnitz 1 - - - - - 1 B 6. Dosinia prostrata Linnaeus 1 1 3 4 14 8 31 B 7. Elizia orbicularis Wood 165 148 23 6 1 - 343 B 8. Felaniella cumingii (Sowerby) 6 4 13 17 8 6 54 B 9. Gafrarium pectinatum (Linnaeus) - 1 16 24 11 22 74 B

10. G. tumidum (Roding) - 1 2 2 3 1 9 B 11. Clauconome chinensis Gray 66 24 7 4 1 2 104 B 12. Hemitapes marmoratus (Lamarck) - 1 6 9 3 3 22 B 13. Laternula anatina Linnaeus - 4 2 3 8 3 20 B 14. Lucina edentula? Linnaeus - - - 1 1 - 2 B 15. Mactrostoma depressa (Spengler) 6 3 3 10 28 9 59 B 16. Meretrix meretrix (Linnaeus) 4 1 - - - - 5 B 17. M. morphina Lamarck 4 3 1 - - 2 10 B 18. Modiolus senhausii (Reeve) 7 1 - - - - 8 S 19. Paphia striata (P. luzonica) (Gmelin) 7 14 26 21 19 13 100 B 20. Pinquitellina pinquis Hanley - - - 2 6 6 14 B 21. Pitar affinis Gmelin - - 1 3 1 4 9 B 22. Soletellina elongata (Lamarck) 37 12 8 - - - 57 B 23. Tellina (Angulus) iridescens (Benson) 1 - 3 11 18 31 64 B 24. Tellina sp. (i) Macoma? - 1 3 6 30 4 44 B 25. Tellina sp. (ii) Angulus sp.? - - 2 1 4 3 10 B 26. Wallucina sp. 1 - 11 40 54 37 143 B

Total no. of Species 14 16 18 19 20 19

Gastropods 1. Batillaria multiformis (Lischke) 113 73 52 97 561 1148 2044 S

Patchy distribution, disappeared from scene 2. Cerithidea cingulata (Potamides

cingulatus) (Gmelin) 2517 2315 3923 6109 1099 348 16311 S 3. Cerithium coralium Kiener 6 19 12 53 313 541 944 S 4. C. lemniscatum Quoy 1 2 6 8 13 23 53 S 5. C. moniliferum (Kierner) 43 72 84 127 315 334 975 S 6. Clithon (Theodoxus) oualaniensis

(Lessen) 1067 1556 1761 1695 318 105 6502 S 7. Melongena pugilina Born - - - 1 1 5 7 S 8. Miniola sp. - - 1 2 4 6 13 B 9. Mitra cf. funeria 2 4 7 15 19 27 74 B

10. Nassarius costatus A. Adams - 1 - 1 2 3 7 S 11. N. jacksonianus (Quoy & Gaimard) 2 16 17 67 66 72 240 S 12. N. muricatus Quoy & Gaimard - - - 2 3 23 28 S 13. N. thersites (Brugiere) 4 4 2 3 1 1 15 S 14. Nerita chameleon Linnaeus 2 1 2 3 - - 8 S 15. Pyrene versicolor (Sowerby) - - - 1 1 5 7 S 16. Strombus isabella Lamarck - - - - - 2 2 S 17. S. urceus Linnaeus - - - - - 4 4 S 18. Syncera (= Assiminea) brevicula

Pfeiffer 160 12 - - - - 172 S 19. Turbonilla sp. - - 2 2 5 6 15 B

Total no. of species at each station 11 12 12 16 15 17




Table 3 (cont.) Stations

Species 1 2 3 4 5 6 Total

Polychaetes 1. Ammaotrypane aulogaster Rathke - - - - 1 9 10 B 2. Arbella iricolor (Montaque) - - - 1 1 1 3 B 3. Aricia sp. - - - 2 32 167 201 B 4. Chone sp. - - 1 - 4 4 9 B 5. Ceratonereis hircinicola (Eisig)? 340 430 109 64 252 211 1406 B 6. Cirratulus cirratus Muller - - - - - 13 13 B 7. Clymene sp. 12 24 108 115 88 107 454 B 8. Diopatra neapolitana Della Chiaje 781 246 37 13 6 11 1094 B 9. Eone sp. - - - - 2 2 4 B

10. Eunice spp. 3 2 - 2 1 2 10 B 11. Glycera sp. 3 6 16 26 26 38 115 B 12. Goniada sp. - 1 2 1 5 7 16 B 13. Hypsicomus phaeotaenia (Schmarda) - - - - 1 2 3 B 14. Lumbriconereis sp. - 1 6 2 20 18 47 B 15. Lysidice collaris Grube - - 4 3 3 1 11 B 16. Marphysa mossambica Peters 5 1 1 8 24 43 82 B 17. Myriochele sp. - - 1 - 1 - 2 B 18. Onuphis sp. 15 23 66 185 213 665 1167 B 19. Ophelia sp. 212 17 3 - 1 1 234 B 20. Owenisfusiformis Delle Chiaje - - 14 69 95 60 238 B 21. Perinereis singaporiensis Grube 173 114 50 33 41 11 422 B 22. Phyllodoce sp. - 3 4 1 7 3 18 B 23. Polychete1 ) 6 - 4 - - - 10 B 24. Polychete 2 -F. Nereidae 2 - 2 - 1 1 6 B 25. Polychete3J 5 1 - 1 1 3 11 B 26. Polyodontes sp. - - - - 1 4 5 B 27. Potamilla leptochaeta Southern - - - - 1 3 4 B 28. Syllidae (one species) - - - 1 3 - 4 B 29. Terebellides stroemi Sars - - - - - 3 3 B

Total no. of species 12 13 17 17 26 26

Crustacea 1. Diogenes diogenes Herbat. 62 81 133 275 488 656 1695 S 2. Dotilla wichmani de Man 15 2 2 - - - 19 SB 3. Macropthalamus transversus (Latreille) 1 - 1 3 2 _ 7 SB

Small specimens seen Aug.-Sept.- Oct. 1969

4. Sphaeromid 1 2 - - - - 3 S 5. Uca marionis (Dana) 19 20 16 8 3 3 69 SB

Coelenterates 6. Cerianthus sp. 5 4 7 8 46 32 102 B 7. Sea anemone - 1 3 6 6 4 20 B

Others 8. Holothuria atra Jaegar - - - - - 3 3 S 9. Lingula unguis (Linnaeus) 2 - 7 21 28 19 77 B

10. Oligochaetes 7 2 1 1 - - 11 B 11. Sipunculus nudus Linnaeus - 1 1 - - 2 4 B 12. Nemertine (1) - 3 4 7 5 2 21 B 13. Nemertine (2) 3 5 2 2 1 - 13 B 14. Nematodes - 3 - 1 2 4 10 B

Total no. of species 9 11 11 10 9 9

S, Surface fauna; B, burrowing fauna; SB, semi-burrowing fauna.



F. C. VOHRA 693

FAUNA OF MATA IKAN

The total number of species listed is over 140 but some of these are not typical of a purely sandy habitat. Most of them were found regularly in the monthly samples but some occurred rather irregularly (Appendix). The whole fauna can be studied under the following categories:

(I) Surface fauna which includes free living forms found exposed on the surface. This comprises gastropods mainly and is marked 'S' in the last column in Table 3. Other common surface organisms not listed in the table include Clibanarius infraspinatus (Hilgendorf), C. padavansis de Man and various microscopic crustaceans and nematodes.

(II) Burrowing fauna comprising forms normally hidden below the surface when the tide is out. This group is mainly characterized by bivalves and polychaetes (see organisms marked B in the last column of Table 3).

(III) Semi-burrowing fauna comprising forms which surface for feeding during low tide. This group contains mostly crabs (Table 3, organisms marked 'SB' in the last column). Other noteworthy species not appearing in the list are Meiomenippe granulosa de Man and Ocypode ceratophthalma (Pallas).

(IV) Enhalus zone fauna comprising mostly the surface dwellers collected during occasional visits to the Enhalus bed at low water extreme tides only. Because of the highly soft nature of the substratum, usual regular samples were not possible from this area. However, the group includes:

Phylum Porifera: Clathria transiens Hallmann, Petrosia testudinaria (Lamarck). Phylum Coelenterata: Cassiopeia sp., Catostylus sp., Cerianthus sp., Gorgonia sp.,

Mastigias papua (Lesson), Peachia sp. ?, Pteroides sp., Zoanthus sp. Phylum Sipunculoida: Sipunculus nudus Linnaeus, S. robustus Keferstein. Phylum Mollusca: (a) Bivalves: Anadara antiquata (Linnaeus), A. granosa (Linnaeus),

Arca auriculata Lamarck, Chione calophylla (Philippi), Laternula truncata (Lamarck), Mytilus viridis Linnaeus, Ostrea sp., Paphia spp. Pinna atropurpurea (Sowerby), P. hanleyi Reeve, Placuna placenta (Linnaeus), P. sella Lamarck, Solen delesserti Chemnitz, Tellina rostrata Linnaeus.

(b) Gastropods: Architectonica perdix (Hinds), Cerithium moniliferum (Kiener), C. morus Lamarck, C. patulum Sowerby, Crepidula walshi(Reeve), Melongena(Semifusus) pugilina Born, Murex capucinus Chemnitz, M. martineanus Reeve, Nassarius hepaticus (Montague), N. thersites (Bruguiere), Pyrenefulgurans (Lamarck), P. versicolor (Sowerby), Strombus isabella Lamarck, S. urceus Linnaeus, Voluta scapha (Gmelin).

Phylum Arthropoda: Clibanarius infraspinatus Hilgendorf, C. padavensis de Man, Diogenes diogenes Herbst, Grapsus spp., Neptunus pelagicus (Linnaeus), Penaeus indicus Milne-Edwards, Scylla serrata Forskal., Squilla spp., Hyastenus sebae Buitendijk.

Phylum Echinodermata: Archaster typicus Mueller & Troschel, Holothuria atra (Jaeger), H. scabra Jaeger, Luidia maculata Mueller & Troschel, Ophiolepis cincta Mueller & Troschel, Pentacta tuberculosa Quoy & Gaimard, Phyllophorus sp., Synaptid.

(V) Alien fauna comprising forms not characteristic of a purely sandy habitat but occurring there on isolated patches of rocks, debris and wood, viz: Arca auriculata Lamarck, Assiminia brevicula Pfeiffer, Drupa mussiva Keiner, Martesia striata Linnaeus, Miniola sp., Modiolus senhausii Reeve, Nassarius olivaceus Bruguiere, Nerita chaemeleon Linnaeus, Pyrene versicolor (Sowerby), Thais echinata (Blainville).

Table 3 shows total numbers of each species collected at each station during the period of study. The more common and interesting of these are as follows.




(I) Surface fauna Diogenes, the commonest hermit-crab became concentrated at station 6 during low

tide, having followed the tide down shore. Gastropods were particularly abundant and varied, Batillaria multiformis being found in all monthly samples from all stations (Table 3), but with concentrated patches occurring in areas overgrown with Halophila ovalis at lower stations (5 and 6). Cerithidea cingulata and Clithon (Theodoxus) oualaniensis, the most widely distributed species on the shore, were obtained in all monthly samples with greater abundance at stations 3 and 4. At upper stations they showed a patchy distribution tending to be absent from the cleaner sand near the stream. Migration up and down the shore seemed to occur in Cerithidea cingulata and this has been dealt with in a separate paper (Vohra, 1970). Cerithium coralium, with its optimum level between stations 5 and 6, seemed to inhabit patches overgrown with Halophila ovalis.

Cerithium moniliferum, sporadic in distribution, was in big concentrations in the Enhalus zone. The species was also found colonizing stones and logs of wood scattered and extending to station 3.

Cerithium lemniscatum, Nassarius jacksonianus and N. muricatus were found in smaller numbers, particularly in the lower stations 5 and 6 (Table 3).

Syncera (Assiminia) brevicula, first noted in samples in June 1958, is more characteristically found on the banks of streams in mangrove swamps around Singapore. Its appearance along with Nassarius olivaceus and Modiolus senhausii (both characteristic of the mangrove swamps) can probably be connected with the changing substratum at the base of the steep slope A (Fig. 3) and the proximity of freshwater seepage.

Nassarius olivaceus was found at station 1 at Mata Ikan, but only occasionally.

(II) Burrowing fauna This constituted the greatest part of the Mata Ikan fauna and its distribution over the

area investigated was less patchy than that of the surface fauna. Thus it is among members of this group that the effects of tidal level on zonation can best be studied.

Amongst the numerous bivalves there was a narrowly midlittoral group concentrated at stations 1 and 2 (Elizia, Glauconome, Meretrix and Soletellina) and a more widely distributed lower midlittoral group (Felaniella, Gafrarium pectinatum, Hemitapes, and Paphia striata) with some preference for stations 3 and 4.

The commonest bivalve of the lowest levels, which are usually called lower littoral by rocky-shore ecologists, was Anomalocardia. Others occurring mostly at the lowest stations included Cyclinella sp., Dosinia, Gafrarium tumidum, Mactrostoma, Pinquitellina, Pitar, Tellina (Angulus) iridescens and Wallucina.

Among polychaetes, Ophelia sp. had its maximum density at station 1, a total of 212 specimens being collected during the period of study (Fig. 12). The other common species at upper stations (1 and 2) included Diopatra and Perinereis which provide a good fishing bait and hence were hunted enthusiastically by fishermen.

Ceratonereis sp. showed a wide range but with concentrations at upper stations (1 and 2) and lower ones (5 and 6). This bimodal distribution suggests that two distinct species may be represented.

Ammotrypane, Lumbriconereis, Cirratulus and Goniada on the other hand were characteristic polychaetes of the lower stations (5-6). The other more widely distributed species of Aricia, Clymene, Glycera, Marphysa, Onuphis and Owenia also showed greater preference for the lower levels.

Of the remaining burrowing and semiburrowing forms Ocypode ceratophthalma lives



F. C. VOHRA 695

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C14 . O ( Cjt

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FIG. 12. (a) and (b). 'Kite' diagrams representing the relative abundance of commonest species along the transect line at Mata Ikan shore.




in a deep burrow about 1 m long at the upper limit of the littoral zone, Dotilla selects clean patches of sand between stations 1 and 2, while Uca can be found all over the beach with preference for the upper levels. Lingula unguis was most common at stations 5 and 6.

Animals which fall outside the scope of this paper include prawns and certain fishes which sometimes occurred in sievings but belong naturally to free-swimming populations and may become stranded in shallows during the receding tide. Barnacles which occurred attached to some shells (dead or alive) and stones, etc. were also left out of sampling counts.

No detailed study was made of microfauna. Occasional examination (July, October 1958, and April 1959) of the top 1 cm layer of the soil, however, showed a considerable number of amphipods, isopods, copepods, ostracods, protozoans (flagellates and ciliates), nematodes and diatoms, etc. Of these, amphipods, copepods and nematodes were most abundant at stations 5 and 6.

Overall results indicate that many animals have their particular zone of maximum

Table 4. Total number of species recorded in faunal surveys on various temperate shores

Author Place No. of species Beanland (1940) Dovey Estuary 30 Bady (1943) Northumberland 27 Colman & Segrove (1955) Stoupe Bank Sands 26 Day et al. (1952) Westford Lagoon 74* Day & Morgans (1956) Durban Bay 25* Holme (1949) Exe Estuary 49 Longhurst (1958) West Africa 60* Macnae (1957) Zwartkops Estuary 66* Macnae & Kalk (1958) Inhaca Island 90t Perkins (1956) Dee Estuary 17 Southward (1953) St Mary 36

Derbyhaven 48 Spooner & Moore (1940) Tamar Estuary 32 Stephenson et al. (1958) Low Isles 49*

* This number refers to the species recorded from sand flats alone. t This number represents only the common species found there. The

actual number recorded is probably greater than this.

abundance on the shore, while others seem to be more evenly distributed over a wider range. 'Kites' in Fig. 12 (a and b) represent the distribution and relative abundance of the more common species along the transect line at Mata Ikan shore. Briefly, the abundant species at upper stations (1-3) are Elizia orbicularis, Ceratonereis, Diopatra, Ophelia, Perinereis and Uca; while at lower stations (4-6) they are represented by Anomalocardia, Wallucina, Batillaria, Cerithium corallium, C. moniliferum, Aricia, Ceratonereis, Clymene, Onuphis, Owenia, Diogenes and Lingula.

DISCUSSION

Faunal comparison The fauna of Mata Ikan comprises more than 140 recorded species out of which about

sixty were collected from the Enhalus zone during occasional visits to the area. The total is much higher than that found in surveys in temperate regions (Table 4). The maximum number of species recorded at a single station in one monthly count was 39 at station 6



F. C. VOHRA 697

(Table 5). The total number of species from Inhaca Island (Macnae & Kalk 1958) compares favourably with that of Mata Ikan. The bulk of the fauna is of tropical origin and is very similar to that of Mata Ikan, more than twenty-five genera including some of their species being common to the two places.

The richness of the fauna at Mata Ikan may indeed be due to the sheltered nature of the site and to the absence of greater fluctuations in temperature. Since very low tides occur either very early in the morning or late in the evening, the lowest levels of the beach, where greater diversity of fauna is noted, are never exposed to the greater heat of the tropical sun. Other possibilities may include continuity in supply of plankton food for filter feeders. In temperate regions only those species that can stand starvation through the unproductive winter months can survive.

Gastropods, lamellibranchs and polychaetes are the most important groups found at Mata Ikan shore. This is in line with various surveys of temperate shores around the British Isles and America.

Table 5. Total number of species collected in monthly samples at each sampling station of Mata Ikan

Stations

Months 1 2 3 4 5 6 Sept. 1957 18 16 26 26 30 39 Oct. 24 18 31 26 32 37 Nov. 16 14 25 35 29 30 Dec. 21 16 26 30 36 36 Jan. 1958 15 14 17 27 27 36 Feb. 13 17 23 23 32 32 March 16 15 23 20 24 24 April 20 11 14 26 26 29 May 15 16 19 21 20 30 June 20 24 16 29 27 34 July 27 19 26 20 31 25 Aug. 21 29 23 33 27 31 Sept. 18 19 27 30 31 31

The Crustacea, however, are poorly represented at Mata Ikan. Crabs, which form the dominant intertidal surface animals in the Brisbane River (Snelling 1959), Java River (Verwey 1930), Low Isles (Stephenson, Endean & Bennett 1958) and various South African estuaries (Day, Millard & Broekhuysen 1952; Day et al. 1953; Day & Morgans 1956; Scott, Harrison & Macnae 1952; Millard & Harrison 1953), are commonly represented, on the collecting stations of Mata Ikan, by Uca marionis, Dotilla wichmani and Macrophthalmus transversus only. Similar paucity of crab fauna has also been noticed in various surveys in the British Isles (Allen & Todd 1902; Percival 1929; Fraser 1932; Alexander, Southgate & Bassindale 1932; Bassindale 1938, Hartley & Spooner 1938; Milne 1940; Beanland 1940; Holme 1949), California (MacGinitie 1935) and the Pacific coast of North America (Ricketts & Calvin 1952).

Most of the polychaete genera, like Marphysa, Owenia, Ophelia, Glycera, Diopatra, Cirratulus, and some lamellibranch genera, e.g. Tellina and Donax, are similar to those found on other shores around Britain (Holme 1949; Colman & Segrove 1955), Africa (Day et al. 1952, 1953; Day & Morgans 1956; Macnae & Kalk 1958 and their co-workers), Gold Coast (Buchanan 1958), Australia (Stephenson et al. 1958), India (Panikkar & Aiyar 1937), Hawaii (Edmondson 1946) and the Pacific coast around Mexico (Ricketts &




Calvin, 1952), and are, therefore, almost universal in their distribution. Most polychaete genera have wide distributions in the tropical Indo-Pacific region. A particularly striking resemblance, however, is seen between the polychaete faunas of Mata Ikan and Inhaca (Macnae & Kalk 1958). The polychaetes of Mata Ikan are burrowing or tubicolous, either active and predatory forms (e.g. Glycera) or less active deposit and filter feeders. Specialized ciliary feeding polychaetes like sabellids and serpulids are present only in the downshore Enhalus zone.

One of the most abundant of the intertidal lamellibranchs of some European shores is Tellina tenuis (Stephen 1929) which is commonly found somewhat below low water mark. At Mata Ikan species of Anomalocardia and Wallucina are more abundant at the lower shore, though species of Tellina do inhabit this level.

In abundance the gastropod fauna resembles that of Low Isles and Heron Island (Stephenson et al. 1958) but in its mode of feeding it differs in being mainly herbivorous. Species of Natica, Terebra and Oliva, so commonly found at Low Isles, are absent from Mata Ikan. The local predators include Nassarius, at stations 1-6, and Melongena and Strombus in the Enhalus zone.

Callianassa, so abundantly present in South Africa (Macnae 1957 and his co-workers), Queensland (Hailstone & Stephenson 1961; Dakin, Bennet & Pope 1952) and America (MacGinitie 1934), is characteristically absent from the Mata Ikan shore. Again Mictyris, the soldier crab of Australian sand fiats (Dakin et al. 1952), is replaced by Dotilla-a genus which is widely represented in the various surveys in South Africa (Day et al. 1952, 1953; Day & Morgans 1956; Macnae 1957), Inhaca (Macnae & Kalk 1958), India (Panikkar & Aiyar 1937) and the Philippines (Edmondson 1946).

As regards the fauna in general, there are many similarities to be noticed between Mata Ikan and Inhaca, Durban Bay and Richard Bay (South Africa). Of the great number of species recorded at Mata Ikan, however, only a few are widespread and abundant throughout the transect studied, while the majority occur in small numbers at few stations (Table 3).

Zonation In comparison with rocky shores very little attention has been paid to the zonation of

animals in sandy shores in general and much less in tropical or subtropical sand beaches, yet it is almost as pronounced as on rocky shores. While reviewing the earlier literature, Dahl (1953) suggested three main zones, based on the distribution of crustaceans and comparable with the tripartite division of rocky shores proposed by Stephenson & Stephenson (1949). His scheme does not apply to the temperate coast of California, where Emerita is the most abundant crustacean of the middle zone. According to Mac- Ginitie (1935) and Pearse, Humm & Wharton (1942), Emerita moves up and down the shore with the tides and therefore it is not wise to name a zone after it. Gauld & Buchanan (1956), while not denying the general validity of Dahl's scheme, have discovered that the West African coast is an area where Ocypode and Talitridae overlap and that the maximum abundance of Excirolina too may exactly coincide with the Ocypode zone. Observations at Mata Ikan, Inhaca, South Africa, Gold Coast, America, Low Islands and various other places confirm Dahl's basic tripartite division of the shore though with different dominant species at each zone in different parts of the world. Further, workers from these regions (Macnae & Kalk, Day and their co-workers; Pearse et al., Stephenson et al., Buchanan & Gauld, etc.) agree with Dahl in so far as they show one of his three principal zones to be that of Talitridae and Ocypode round about high water mark.



F. C. VOHRA 699

The studies of Stephen (1929), Pearse et al. (1942), Watkin (1942) and Colman & Segrove (1955) suggest that to Dahl's cirolanid zone there may be added, as widespread features of sandy beaches, a Donax zone and a Nerine zone. In the opinion of the present author the second midlittoral zone of Dahl can easily be split into sub zones (see p. 694). The lowest zone, which is inhabited by some sea grass (Enhalus at Mata Ikan, Zostera in many British, Australian and African shores, and Cymodocea in Inhaca) and can thus similarly be termed the 'eel grass zone', lies at about low water of spring tides, so evidently corresponds with the Laminaria zone of rocky shores and must be termed the infralittoral fringe.

The Mata Ikan shore can thus be divided fairly clearly into the following main zones: (1) Ocypode zone (Supralittoral fringe) (2) Midlittoral zone (3) Enhalus zone (Infralittoral fringe)

Below these lies the infralittoral zone. Although no work was done there, it is believed that there may be a more pronounced change in species composition in this area. Such a change has already been reported in the North Pacific by Shelford et al. (1935), but according to Holme (1953) and Sanders (1956) pelecypods and annelids are still pre- dominant in this zone. The three main zones at Mata Ikan support very different types of animals and a pattern of zonation is seen within each. The Ocypode zone is composed of loose, rather dry, sand, which harbours no macroscopic fauna in its top 5 cm layer. 0. ceratophthalma and Perinereis sp. are found in much deeper layers where some moisture is always retained. Ocypode ceratophthalma is also dominant on Malayan shores, e.g. Mersing, Penang and Port Dickson (personal observations), Hawaii (Edmondson 1946), Queensland (Stephenson et al. 1958), Christmas Island (Andrews 1900), Inhaca (Macnae & Kalk 1958), South African estuaries (Day and his co-workers) and Madras (Panikkar & Aiyar 1937). Other species of Ocypode are widely distributed throughout the Indo- Pacific region (Rathbun (1921) in Congo; Mayer (1905) in North America; Crane (1941) on the west coast of Tropical America; and Dakin et al. (1952) in New South Wales). In brief the Ocypode zone of Snelling (1959) is slightly different, because the crabs of the subfamily Ocypodinae which occur in the Brisbane River are dwellers around H.W.N. and not H.W.S.

The midlittoral region is totally covered by all high tides but is not entirely exposed by all low tides, since some neap tides recede only to about station 4. The flora here is very poor compared with the fauna, of which eighty-eight species have been recorded, compared with forty-nine at Low Isles in subtropical Australia (Stephenson et al. 1958), 47* at Inhaca and 45 at Zwartkops estuary (Macnae 1957).

Analysis of the fauna of this zone at Mata Ikan reveals a subzonation, which in some cases is well marked (Elizia at stations 1-2, Tellina at stations 5-6), while in others, where individuals occur over a broader area of the zone, it is less definite (e.g. Hemitapes marmoratus, Paphia striata, Table 3). Of the surface gastropod fauna Cerithidea cingulata and Theodoxus oualaniensis are the most abundant.

The upper region of this zone has a well-drained patch of clean brown sand, overlying a black layer. This drier patch of oxidized sand harbours Dotilla. The presence of this crab has also been reported in similar habitats of well-drained sand, by Macnae & Kalk (1958) at Inhaca, Day & Morgans (1956) in Durban Bay and by their co-workers in other parts of South Africa. Of the rich burrowing fauna Ophelia (polychaete) and Elizia (bivalve)

* This number represents only the common species found there. The actual number recorded is probably greater than this.




are found in the Dotilla habitat. This 'Elizia zone' at M.T.L. seems just as distinct as the L.W.N.T. zones of Davila recorded by Stephenson et al. (1958) at Low Isles and Donax of Gauld & Buchanan (1956) on the Gold Coast and of Pearse etal. (1942) at Beaufort, N.S. Uca also occurs at M.T.L., its distribution along with Macrophthalmus and Scylla serrata following the same general pattern as in the Brisbane River (Snalling 1959), Java River (Verwey 1930) and Inhaca (Macnae & Kalik 1958).

On most shores, as Durban Bay (Day & Morgans 1956), there is a progressive increase in number of species from high water mark to low water mark. At Mata Ikan a similar general pattern prevails, the number of species increasing steadily from forty-five at station 1 to seventy-one at station 6 (Table 1). As in Durban Bay the animal populations are denser and more varied in muddy than in clean sand. The total numbers of species collected in monthly samples at each station are shown in Table 5. It is interesting to note that minimum numbers of species were found at each station during the period February- July, particularly during March and April.

The Enhalus zone at Mata Ikan is muddy with much shell gravel and standing water. This is the local equivalent of the Cymodocea fields at Inhaca. Both these zones form the lowest sections of the intertidal fiats which are exposed at low spring tides. Both are covered with dense vegetation which provides food and shelter to their associated greater wealth fauna. Many genera like Holothuria, Synapta, Murex, Trochus, Chione, Anadara, Scylla, Clibanarius, etc. are common in both areas. These zones are comparable with the Zostera zone in temperate regions.

Like other zones at Mata Ikan, the Enhalus zone has its own characteristic fauna, much of which is dependent on the growth of Enhalus but sometimes strays into the midlittoral zone.

Causes of zonation There has been much discussion in the literature concerning the relative importance of

variable factors in determining the zonation of intertidal animals. According to Spooner & Moore (1940) and Emery et al. (1957), some species maintain their relation to a particular tidal level even where there is no change in the substratum. In the opinion of Stephen (1953) the zones are related to the interface between air and water, wave action, sunshine and competition for food and space. Brady (1943) and Evans (1957) argue that the periods and frequencies of submergence or emergence are particularly important factors. Holme (1949), Gunter (1950), Webb (1956), Moore (1958) and Teal (1958) stress the importance of salinity and/or the nature of the soil in determining the distribution of animals.

Allen (1899), Ford (1923), Davis (1925), Smith (1932), Wilson (1937, 1948, 1952), Panikkar & Aiyar (1937), Dahl (1946,1953), Thorson (1946), Chapman (1949), Chapman & Newell (1949) and many more workers in Africa and elsewhere emphasize the importance of the composition and physical properties of soil. Petersen (1915, 1918), while not denying the importance of sediments in determining the nature of the community, con- siders predation and competition to be particularly important.

Soil temperature and exposure to air are closely linked with the tidal factor. The highest collecting station at Mata Ikan is exposed seven times as long as the lowest. Accordingly the soil at the upper stations suffers greater variations in daily temperature and is liable to more desiccation than at the lower stations. The greater temperature at the landward fringe and on the slope A (Fig. 3) may explain the complete absence of the marine fauna in the upper 5 cm layers. As this range decreases downshore the number of



F. C. VOHRA 701

species increases. On the other hand temperature ranges are smaller below the surface and many animals are able to burrow during the period of exposure.

Drainage may be of particular importance on the top shore at Mata Ikan where there are marked changes in the fauna. Most of the species including Tellinids, common on the rest of the shore, are absent here but Dotilla and Ophelia are commonly found, as in similar environments elsewhere (Holmes 1949; Macnae & Kalk 1958, etc.). The intertidal distribution of most other species, however, cannot be explained in terms of drainage alone.

On the Mata Ikan shore, salinity and pH values of interstitial water at different stations show variations too small to be judged as having a far reaching influence on the zonation of the burrowing fauna. In spite of longer exposure and a higher temperature range at upper stations, salinity of interstitial water at these places remains low and stable, no doubt because of rain, high humidity, cloud cover and seepage of freshwater. The salinity of surface waters, however, has a wide range of variations (7-31 4%.), which will affect mostly the surface dwellers, e.g. Cerithidea cingulata and Theodoxus (= Clithon) oualaniensis. These were seen to be limited to regions of low salinity and pH.

Soil grades from various stations at Mata Ikan did not vary greatly from the average for the whole shore. Only the fractions of stone, medium and fine sand showed some considerable variation. Evidence from Mata Ikan and other shores suggests that soils with approximately 4500 of coarse sand (500-2057 Iu) and 25-30% of medium sand (211- 500 ,u) provide suitable environments for most burrowing animals. Finer grades, though capable of retaining more water, are more closely packed and thus have less oxygen circulating through them. At Mata Ikan the general fauna did not seem to be limited by this factor, for the abundance of burrowing forms (individuals as well as species) increased with increasing proportions of the finer soil grades. Certain species, however, may have been adversely affected.

Surface animals, especially gastropods, e.g. Cerithidea cingulata, Theodoxus oualaniensis, Nassarius jacksonianus, N. thersites, etc. seem unlikely to be limited by soil grades. Glauconome chinensis, Elizia orbicularis, Soletellina elongata and Ophelia sp. on the other hand are more common in the much coarser grades (e.g. at station 1). The distribution of Ophelia is probably limited by both drainage and soil grades and neither by drainage alone (Holmes 1949) nor by soil alone (Wilson 1948).

The nature of the shore soil along with the animal's own physiological needs (food and feeding habits, spawning and material for tubes, etc.) would appear to affect the distribution and population densities of various animals. It is not possible, however, to separate this factor completely from other effects related to differences in shore levels, and it is likely that some animals are more strictly limited by soil conditions, others more strictly by times of emergence and submergence, and yet others by additional factors.

Movements on the beach Many organisms are known to migrate up and down the beach either with the tide or

seasonally (MacGinitie 1938; Pearse et al. 1942; Mori 1938, 1950; Hedgpeth 1957; Jacobson 1955). On the Mata Ikan shore Diogenes exhibited this movement with the tide while Cerithidea cingulata showed a seasonal migration controlled perhaps by internal physiological rhythms. The tidal migrations are presumably associated with feeding and the need for moisture.

In addition to its seasonal migration, C. cingulata also showed segregation by size in relation to tidal levels, the biggest individuals being found at the upper stations (1-2).




A similar distribution has also been noticed in the case of Pismo clams (Weymouth 1923), toheroa (Rapson 1952), Thoracophelia mucronata (Dales 1952), Cardium edule and Tellina tenuis (Stephen 1953). Some of these have their bigger individuals upshore, while others have smaller ones there and whether this difference is due to migration of the year groups or better growth at one particular level would appear to depend on the individual species and its mode of life.

ACKNOWLEDGMENTS

My sincere thanks are due to Professor R. D. Purchon and Professor A. J. Berry for constant encouragement and helpful criticism during the present study.

I am greatly indebted to Professor Tucker Abbot and Dr D. S. Johnson for their valuable assistance in checking the identification of molluscs and crustaceans respectively. Mr Eric Alfred, Curator of Raffles Museum, Singapore, kindly allowed me to compare my specimens with the named collection in the museum. Secretarial help by Miss Kuan Lai Wah in typing this manuscript is also acknowledged.

Finally I wish to acknowledge the grant of a scholarship by the Government of the Federation of Malaya which enabled me to undertake this work.

SUMMARY

(1) Monthly quantitative collections of the macrofauna were made for one year along a traverse of sandy shore at Mata Ikan.

(2) The species which inhabit this shore are listed and exceed 140. While some are more or less uniformly distributed, others show marked zonations which are compared with those of temperate and other regions.

(3) Bivalves and polychaetes form the bulk of the macrofauna. (4) Measurements of salinity, temperature, pH, tidal coverage and grading of soil

particles show differences in physical conditions at different stations along the traverse. (5) Salinity and temperature are more stable at depth, so only the animals which live on

the surface have to be capable of adapting themselves to large variations. Most of these animals are gastropods, which are capable of closing their opercula in unfavourable conditions.

(6) The soil composition is relatively uniform, but the fractions of stone, medium sand, and fine sand show some variations. Conclusions as to the role of the soil as a limiting factor are rather difficult to draw.

(7) Variations in temperature and duration of exposure seem likely to be most signifi- cant in controlling the zonations of the animals.

(8) Animals are exposed to higher temperatures than those found around temperate shores, but the range of temperature variation is moderated by climatic and tidal conditions.

(9) The relative importance of several factors in supporting a rich fauna and determining its distribution is discussed.

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(Received 7 March 1971)



0

APPENDIX

Monthly total numbers of individuals of each species collected from Mata Ikan Shore during the period of study, September 1957-58

Species Sept. Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept. Total Bivalves

1. Anomalocardiasquamosa 22 19 20 19 10 15 17 12 12 15 13 34 13 221 2. Arca auriculata - - - - 1 - - - - - - 1 - 3 3. Crassatellites radiata - - - - - - - - - - 1 - 1 N 4. Cyclinella sp. (young of C. sinensis?) 3 1 - - - _ _ _ 1 _ _ 1 _ 6 t 5. Donaxfaba - - - - - 1 - - - - - - - 1 I 6. Dosinia prostrata 5 3 2 3 1 1 - 3 - 5 2 3 3 31 O 7. Elizia orbicularis - - - - - - - - - 25 164 79 75 343 8. Felaniella cumingii 8 6 6 5 5 3 2 1 2 1 4 7 4 54 t 9. Gafrariumpectinatum 11 13 5 11 1 3 5 1 2 5 6 6 5 74 t

10. G. tumidum 1 2 - 1 - - - - - 2 - 1 2 9 > 11. Glauconome chinensis 2 5 4 4 3 - - 3 1 21 26 22 13 104 12. Hemitapes marmoratus - 5 1 1 1 3 - - 1 4 - 4 2 22 ; 13. Laternula anatina 2 2 1 - 1 1 - - 1 1 7 1 3 20 14. Lucina edentula? - - - - - - - - - - - 2 - 2 | 15. Mactrostoma depressa 12 9 3 4 4 4 - 3 1 2 9 8 - 59 16. Meretrix meretrix 2 - 1 - - - 1 - - 1 - - - 5 17. M. morphina? 3 4 1 - 1 - - - - 1 - - - 10 18. Modiolussenhausii - - - - - - + - - - 8 - - 8 ? 19. Paphia striata (P. luzonica) 15 8 17 6 8 8 6 7 2 6 7 8 2 100 20. Pinquitellinapinquis 3 1 2 1 - - - - 2 1 - 1 3 14 21. Pitar affinis 2 1 2 2 - - 1 - - 1 - - - 9 22. Soletellina elongata 2 1 - 1 3 - 2 3 1 18 18 3 5 57 23. Tellina (Angulus) iridescens 6 3 4 7 3 3 6 5 5 10 6 5 1 64 24. Tellina sp. I Macoma? 2 2 6 - 2 2 3 2 1 11 5 4 4 44 25. Tellina sp. 2 Angulus? 2 - - - - 1 - 2 - 4 1 - - 10 26. Wallucina sp. 11 15 19 12 13 15 7 5 9 5 7 7 18 143



Species Sept. Oct. Nov. Dec. Jan. Feb. March April May June July Aug. Sept. Total

Gastropods 1. Batillaria multiformis 10 262 359 318 873 67 49 10 3 3 5 31 54 2044 2. Cerithidea cingulata 1743 1591 1432 1293 1332 866 908 1059 953 1026 1319 1244 1545 16311 3. Cerithium corallium 163 146 105 75 85 62 14 7 16 15 34 105 117 944 4. C. lemniscatum 9 9 5 8 6 1 1 - - 4 3 3 4 53 5. C. moniliferum 86 251 131 102 98 62 22 26 18 21 39 32 87 975 6. Clithon (= Theodoxus) oualaniensis 724 667 556 512 508 526 406 458 267 384 465 448 581 6502 7. Melongena pugilina - - - 1 - 1 1 - - 1 1 1 1 7 8. Miniola sp. 3 1 1 2 - - 1 2 1 - 1 - 1 13 9. Mitra cf. funeria 5 8 6 7 5 3 5 8 8 6 4 4 5 74

10. Nassarius costatus 2 - - 2 - - - - 1 1 1 - - 7 11. N. jacksonianus 27 46 19 32 19 14 12 8 12 7 8 18 18 240 12. N. muricatus 4 6 4 8 2 2 - - - - 1 - - 28 13. N. thersites - 1 1 1 - 2 1 - 2 2 1 1 3 15 14. Nerita chameleon - 1 - 1 - - - 1 1 - 1 2 1 8 1 15. Pyrene versicolor 2 - 1 1 - 1 - - 1 - - - 1 7 16. Strombus isabella - 1 - - - - - - - - - 1 - 2 17. S. urceus - 1 - - 1 - - - - - 1 - 1 4 0 18. Syncera (=Assiminea) brevicula - - - - - - - - - 55 24 14 79 172 =

19. Turbonilla sp. - 2 6 2 1 - - 1 - - 1 2 - 15

Polychaetes 1. Ammotrypane aulogaster - - 1 5 - 1 - 1 - 1 - - 1 10 2. Arabella iricolor 1 - 1 - - 1 - - - - - - - 3 3. Aricia sp. 5 14 9 20 20 26 6 18 8 25 26 20 4 201 4. Chone sp. 4 - - 1 - 1 - - - - 1 1 1 9 5. Ceratonereis hircinicola? 142 91 93 73 59 50 46 13 31 56 197 186 369 1406 6. Cirratulus cirratulus 1 1 - 4 1 1 1 1 - - 2 - 1 13 7. Clymenesp. 67 60 82 35 32 39 22 12 16 10 13 33 33 454 8. Diopatraneopolitana? 33 21 28 62 134 72 96 185 66 63 111 111 112 1094 9. Eone sp. 1 - - - - - 1 - - 1 - - 1 4

10. Eunice spp. - 5 1 - - - 1 - - - 1 1 1 10 11. Glycerasp. 3 7 4 3 5 7 6 12 9 12 17 19 11 115 12. Coniada sp. 2 1 2 3 2 - - 1 1 3 - - 1 16 13. Hypsicomusphaeotaenia - - - 1 - - - 1 1 - - - - 3 14. Lumbriconereis sp. - 5 3 24 10 2 1 - - 1 - - 1 47

0



00

A ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~ ~~~~~~~~~~~~~~~~~0 APPendix (cont.)

15. Lysidice collaris 1 - 1 - 1 1 1 - 1 2 1 - 2 11 16. Marphysa mossambica 8 3 4 7 7 9 4 7 7 8 7 7 4 82 17. Myriochzele sp. - 1 1 - - - - - - - - - - 2 18. Onuphis sp. 76 131 110 105 100 103 80 82 89 86 81 56 68 1167 19. Ophelia sp. 11 42 14 10 14 12 9 6 1 47 18 26 24 234 20. Owenia fusiformis 22 20 18 11 17 19 13 19 18 17 18 20 26 238 21. Perinereis sp. 26 13 36 31 36 16 41 47 51 49 1 1 9 56 422 22. Phyllodoce sp. 2 3 2 2 1 2 - 2 - 1 3 - - 18 23. PolychaetelI 1 3 1 3 - 1I - - - - 1I 10 N 24. Polychaete 2 F. Nereidae 1 2 - 1 - 2 - - - - - - - 6 ;:

25. Polychaete 3 - 1I - - 3 - - 1 2 - 11 . 26. Polyodontes sp. - 1 1 - - - - 1 1 - - 1 - 5 27. Potamilla leptochaeta - - -1 - - - 1 - - - 1 1 4 28. Syllidae (Single species) - 1 1 1 - 1 - - - - - - - 4 29. Terebellides stroemi - - 1 - - - - - - - - 1 1 3

Others 1. Chiton - 1 1 - - - - - - - - - - 2 2. Diogenes diogenes 151 214 264 240 123 122 66 24 103 75 77 82 154 1695 3. Dotillawichmanii 1 1 2 4 2 1 2 1 1 1 - 1 2 19 4. Macropthalamus transversus - 2 - - - - - - - 1I 2 2 7 5. Sphaeromid - - - - - - - - 1 2 - - - 3 6. Uca marionis 10 11 9 5 3 3 4 2 7 2 4 6 69 Z- 7. Cerianthzus 5 3 8 3 5 2 - 6 6 15 17 26 6 102 8. Sea anemone 2 3 1 2 1 2 1 2 1 1 2 1 1 20 9. Holothuria atra - 1 - 1 - - - - - 1 - - - 3

10. Lingula unguis 6 3 4 4 8 3 5 7 6 8 7 10 6 77 11. Oligochaetes 2 2 1 1 - 1 - - 1 - 1 1 1 11 12. Sipunculus sp. - - - - - 1 1 - - - 1 1 - 4 13. Nemertinel1. 1 3 2 - 1 3 3 1 1 2 2 - 2 21 14. Nemertine 2. - - - - 1 1 3 1 1 2 1 1 2 13 15. Nematodes 1 I 1 1 1 - - - 3 - - 2 10

Species caught otherwise are not listed in the Appendix.



zonation on a tropical sandy shore

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