IMPACTS OF MANGROVE CONSERVATION ON GROWTH

AND ABUNDANCE OF GASTROPOD Terebralia palustris IN

MICHAMVI ZANZIBAR, TANZANIA

Moyoni Abdi Khatib

M.Sc. Biodiversity Conservation

University of Dar es Salaam

April 2015

IMPACTS OF MANGROVE CONSERVATION ON GROWTH

AND ABUNDANCE OF GASTROPOD Terebralia palustris IN

MICHAMVI ZANZIBAR, TANZANIA

By

Moyoni Abdi Khatib

A Dissertation Submitted in Partial Fulfillment of the Requirements for the

Degree of Master of Science in Biodiversity Conservation of the University of

Dar es Salaam

University of Dar es Salaam

April 2015

i

CERTIFICATION

The undersigned certify that they have read and hereby recommend for acceptance

by the University of Dar es salaam a dissertation entitled: Impacts of Mangrove

Conservation on Growth and Abundance of Gastropod Terebralia palustris in

Michamvi Zanzibar, Tanzania in partial fulfillment of the requirements for the

degree of Master of Science in Biodiversity Conservation of the University of Dar es

Salaam.

……………………………………………

Dr S.G.M Ndaro

(Supervisor)

Date: --------------------------

……………………………………………

Dr N.S. Jiddawi

(Supervisor)

Date: -------------------------

ii

DECLARATION

AND

COPYRIGHT

I, Moyoni Abdi Khatib, hereby declare that this work is entirely a result of my own

original work except where acknowledged in the text. It has not been presented and

will not be presented to any other University for a similar or any other degree award.

Signature ---------------------------

This dissertation is a copyright material protected under the Berne Convention, the

Copyright Act 1999 and other international and national enactments, in that behalf,

on intellectual property. It may not be reproduced by any means, in full or in part,

except for short extracts in fair dealings, for research or private study, critical

scholarly review or discourse with an acknowledgement, without the written

permission of the Directorate of Postgraduate Studies, on behalf of both the author

and the University of Dar es Salaam.

iii

ACKNOWLEDGMENT

I wish to express my grateful thanks to my supervisors Dr S.G.M Ndaro (Department

of Aquatic sciences and Fisheries) and Dr N.S.Jiddawi (Institute of marine science)

for their helpful intellectual advice and supervision in the whole period of conducting

this study. I give special thanks to Mr. Ahmada Soud Ame the leader of the conserved

mangrove forest in Michamvi kae (Kibidukani) for providing permission for carrying

out the study in the forest, cooperation and providing information concerning the

study.

I wish to express special thanks to Mr. Said Juma (Technician at IMS), Mr. Haji

Abdi Khatib, Machano Haji, Abdul- azizi and Ame Juma Ame for their great

experience and help in the whole activities of data collection.

I wish also to express my thanks to Tutorial Assistants at University of Dar es

salaam, Mr. Mohamed Kibaja, Steven Temu and Lyakurwa John for their careful

advice on data analysis and report writing of this study.

I specifically thank Mr. Mtumwa Mwadini of the Institute of Marine Science (IMS),

for guidance in field work and analysis of the samples, may God bless him.

I sincerely thank my husband, mother, brothers and sisters for their support during

the entire degree program. Their encouragement and prayers gave me peace and

improved my performance.

iv

DEDICATION

I dedicate this dissertation to my lovely husband, and my children Zainab, Nusayba

and Abdul wahid; their love, tolerance and encouragement which substantially

contributed to the completion of this work.

v

LIST OF ABBREVIATIONS

CBC - Community Based Conservation

PES - Payment for Ecosystem Services

FSG - Frequency of Size Group

vi

ABSTRACT

Mangrove conservation in Michamvi village is through Community Based

Conservation (CBC) established in 2000. The impact of mangrove conservation on

the gastropod Terebralia palustris in Michamvi, Zanzibar has not been documented.

The aim of this study was to determine the impacts of mangrove conservation on

growth and abundance of T. palustris in conserved and unconserved mangrove forest

of Michamvi. The study was undertaken for two months, January and February 2014.

Sampling was done on three transect lines in each site.

The abundance of T.palustris was found to be not significantly higher between

conserved and unconserved mangrove forest. The distribution of adults and juveniles

was significantly higher in conserved than in unconserved mangrove forest; also the

length weight relationship showed significant positive relationship between

conserved and unconserved mangrove forest. The factors that affected abundance of

T.palustris were destruction of mangrove forest, alteration of habitat and

overharvesting. From this study I conclude that mangrove conservation increases the

abundance and growth of T.palustris while mangrove destruction and overharvesting

(of the gastropods) decreases their abundance and growth.

I recommend that a ban on mangrove clearance and waste disposal be imposed, and I

propose future study to cover a longer time on more distant sites to be able to get

more information of a related study.

vii

TABLE OF CONTENT

Certification…................................................................................................................ i

Declaration and Copyright ............................................................................................ ii

Acknowledgment ......................................................................................................... iii

Dedication…… ............................................................................................................ iv

List of Abbreviations..................................................................................................... v

Abstract……… ............................................................................................................ vi

Table of Content .......................................................................................................... vii

List of Tables................................................................................................................. x

List of Figures. ............................................................................................................. xi

List of Plates… ............................................................................................................ xii

List of Appendices ..................................................................................................... xiii

CHAPTER ONE: INTRODUCTION ....................................................................... 1

1.1 General Introduction ............................................................................. 1

1.2 Statement of the research problem ........................................................ 4

1.3 Objectives .............................................................................................. 4

1.4 Research Hypotheses ............................................................................ 5

1.5 Significance of the Study ...................................................................... 5

1.6 Literature Review .................................................................................. 6

1.6.1 Abundance............................................................................................. 6

1.6.2 Distribution .......................................................................................... 7

1.6.3 Factors Affecting Distribution and Abundance .................................... 7

viii

1.6.4 Growth .................................................................................................. 8

1.6.5 Feeding Ecology.................................................................................... 9

1.6.6 Ecological Role ................................................................................... 10

CHAPTER TWO: MATERIALS AND METHODS ............................................. 11

2.1 Description of the study area............................................................... 11

2.1.1 Geographical location ......................................................................... 11

2.12 Hydrology ........................................................................................... 12

2.13 Climate ................................................................................................ 13

2.1.4 Social economic activities ................................................................... 13

2.2 Description of the study site. ............................................................... 14

2.2.1 Conserved mangrove forest at Michamvi ........................................... 15

2.2.2 Unconserved mangrove forest at kinani .............................................. 16

2.3 Data collection .................................................................................... 17

2.3.1 Sampling for T.palustris ..................................................................... 17

2.3.2 Sampling of the soil ............................................................................ 18

2.3.3 Sampling of sea water ......................................................................... 19

2.3.4 Measurement of salinity and temperature ........................................... 19

2.4 Data analysis ....................................................................................... 19

CHAPTER THREE: RESULTS .............................................................................. 21

3.1 Abundance of Terebralia. palustris in conserved and unconserved

mangrove forest ................................................................................... 21

ix

3.2 The size frequency distribution of T. palustris in conserved and

unconserved mangrove forests ............................................................ 22

3.3 Length and weight of T. palustris in the conserved and unconserved

mangrove forests. ................................................................................ 23

3.3.1 Length weight relationships of T. palustris in conserved and

unconserved mangrove forests ........................................................... 23

3.4 Variations in length and weight of T. palustris between conserved and

unconserved mangrove forests. ........................................................... 25

CHAPTER FOUR: DISCUSSION .......................................................................... 26

4.1 Impact of mangrove destruction on abundance of T. palustris ........... 26

4.2 The size frequency distribution of T.palustris in Conserved and

Unconserved mangrove forest............................................................. 29

4.3 The length weight relationships of T.palustris in conserved and

unconserved mangrove forest ............................................................. 31

CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS ................. 32

5.1 Conclusions ......................................................................................... 32

5.2 Recommendations ............................................................................... 33

REFERENCES .......................................................................................................... 35

APPENDICES ........................................................................................................... 42

x

LIST OF TABLES

Table 2. 1: Distribution of main income generating activities in Chwaka Bay

area. .................................................................................................... 14

Table 2. 2: Main income generating activities by gender in the Chwaka Bay

area. .................................................................................................... 14

xi

LIST OF FIGURES

Figure 2. 1: Map of Chwaka bay showing the study sites,Michamvi kae

(kibidukani) site 1 and Kinani site 2................................................... 12

Figure 3. 1: Mean abundance of T. palustris (Mean±SE) in conserved

(site 1) and un conserved mangrove forest (site 2) ........................... 21

Figure 3. 2: Mean abundance of T. palustris in transects of conserved and

unconserved mangrove forests of Michamvi village, Zanzibar ......... 22

Figure 3. 3: Size frequency distributions of adults and juveniles between

conserved and unconserved mangrove forests of Michamvi

village, Zanzibar (FSG = Frequencies of size groups of

T. palustris) ......................................................................................... 23

Figure 3. 4: The length weight relationship of T.palustris in conserved

mangrove forest. ................................................................................. 24

Figure 3. 5: The length weight relationship of T. palustris in unconserved

mangrove forest. ................................................................................. 24

xii

LIST OF PLATES

Plate 2. 1: The conserved mangrove forest at Michamvi village, the area

known Kibidukani mangrove forest.( Field photo). ........................... 16

Plate 2. 2: Unconserved mangrove forest at Kinani mangrove forest

Michamvi, Zanzibar with fallen logs and young mangrove plants.

(Field photo) ....................................................................................... 17

Plate 2. 3: T. palustris in the field, most of the time occurs in a cluster ............... 18

xiii

LIST OF APPENDICES

Appendix 1: Abundance of T.palustris along the three transect lines of Conserved

mangrove forest. ................................................................................... 42

Appendix 2: Abundance of T.palustris along three transects line of unconserved

mangrove forest. ................................................................................... 43

Appendix 3: The abundance of T.palustris in both Conserved and unconserved

mangrove forest. ................................................................................... 44

Appendix 4: Show the percentage of organic matter content of the sediments in

site1 and site 2 ....................................................................................... 45

1

CHAPTER ONE

INTRODUCTION

1.1 General Introduction

Mangrove forests are comprised of taxonomically diverse, salt tolerant species of

trees and shrubs that thrive in intertidal zones of sheltered tropical and warm

temperate shores and estuaries throughout the world (Macnae, 1968; Yamanda,

1998). The importance of mangroves as a major nursery ground and habitat provider

for a whole range of marine species, many with greater ecological and economical

importance, is well known (Robertson and Duke, 1987; Semesi, 1998).

Mangroves of Zanzibar make up the second largest natural forest in Tanzania (after

Rufiji) with very diverse aquatic fauna composition including mammals (Red

colobus and Sykes monkey, Ader’s duiker, suni Antelope and blue duiker), molluscs

, crustaceans, fish, insects and other terrestrial fauna including reptiles and birds Akil

and Jiddawi, (2001); Mchenga and Rashid, (2010). Human disturbance has resulted

in more than 50% of the world’s mangrove forests being destroyed Spalding et al.,(

2010). This huge loss of mangrove forests globally, has been attributed to urban

development, aquaculture, mining along coastal zones and overexploitation of fauna

and flora of mangrove forests Walters, (2005); Walters et al.,( 2008); Kairo et al.,

(2008); Alongi, (2009).

In Michamvi village some species of mangrove are more exploited than others, for

example Ceriops tagal is the most exploited species accounting for 45%, followed by

Bruguiera gymnorriza accounting for 21% while Rhizophora mucronata accounts for

2

16%. The other species are minimally affected by exploitation. Shunula and

Whittick, (1996). Predictions suggest that all mangroves forests could be lost in the

next 100 years if the present rate loss continues Duke et al., (2007).

Gastropods have been reported in various mangrove forests of Zanzibar Akil and

Jiddawi, (2001) and live on and in the muds, firmly attached to the mangrove roots or

forage in the canopy Kathiresan and Bingham, (2001) .Only few studies on

mangrove fauna have been conducted in Zanzibar Ngoile and Shunula, (1992); Akil

and Jiddawi, (2001).

As in other parts of the world mangroves of Zanzibar are threatened by destruction

intimately linked with human activities, such as logging for timber and cutting for

fuel wood Mkomwa, (1992); Shunula and Whittick, (1996); Semesi, (1998).Major

forest product harvested from mangrove forest includes timber beams, withies,

upright poles, rippers and fuel wood for domestic use and for charcoal and lime

burning. Shunula and Whittick, (1996); Mohammed and Jiddawi, (1999).

A number of prominent mangrove-dwelling species are indeed known to remove and

consume leaf litter, in particular sesarmid crabs (e.g Lee, (1998) and species such as

Ucides cordatus (crab) Nordhaus et al., (2005) and the gastropod Terebralia

palustris Slim et al., (1997). T. palustris (Linnaeus, (1767) is the largest snail species

found in the mangrove habitats, commonly reaching 120 mm in length, and

occasionally as much as 190 mm. Ecologists view that mangroves provide shelter

and food sources for animals such as T. palustris. Crabs and gastropods are the two

3

major mangrove seed eaters in forests, and thus play an important role in determining

plant community structure Smith et al., (1989). A number of gastropod genera (e.g.

Ellobium, Enigmonia, Littoraria and Terebralia) appear to occur exclusively in

mangrove systems Plaziat,(1984).

T. palustris whose habitat is mangrove forest is equipped with thick, heavy, conical

shell with long pointed spire, up to 12cm, Linnaeus,(1767). It has whorls with strong

axial ribs crossed by deeply incised spiral grooves; its colour is dark brown. They are

located in upper eulittoral mud or in mangrove swamps.

The distribution of T. palustris is Indo-Pacific and the local name of the species in

Kiswahili is Suka Richmond, (1997). Previous studies by Plaziat (1997) and

Houbrick (1991) on the T. palustris suggest that it may play an important role in

decomposing mangrove detritus. It has been recorded that T. palustris graze on the

sediment as well as on mangrove litter, including leaf, stipule, calyx, fruit and

propague Nishihira, (1983).

Currently, wild gastropods of the species T. palustris Linnaeus, (1767) have been

reported in Mbweni Akwilapo, (2001), Mtoni Machumu, (1996), Bagamoyo

Kayombo, (1988); Mgaya et al., (1999), and Rufiji Stedman-Edwards, (2000).

The only known predator of T. palustris is the mud crab, Scylla serrata Houbrick,

(1991). T. palustris is also collected by humans, often in great numbers; the fleshy

4

part is primarily sold at local market for food and also used as bait, Mgaya et al.,

(1999).

1.2 Statement of the research problem

It is clear that invertebrate species are poorly documented globally; complete species

list for most invertebrates are currently impossible to produce even for a small

habitat. This lack of knowledge can be serious impediment to the effort of their

conservation New, (1995). Hence their conservation becomes infeasible and not even

considered in most cases. The same problem occurs in mangrove forest of Michamvi

village. Most research carried out in Michamvi village and published has been

focusing on fishing, fish products and mangrove conservation. No research has been

conducted so far to explain the importance of mangrove conservation on the

gastropod T. palustris or other marine invertebrates. The study compares abundance,

distribution and growth parameters of T. palustris in conserved mangrove areas of

Michamvi at Kibidukani to areas affected by human activities at Kinani.

1.3 Objectives

The main objective of the study is to determine the impact of mangrove conservation

on growth and abundance of T. palustris in Michamvi village, Zanzibar.

The specific objectives are:

To determine the abundance of gastropod T. palustris in conserved and un

conserved mangrove forest of Michamvi village.

To determine size frequency distribution of T. palustris in conserved and un

conserved mangrove forest of Michamvi village.

5

To determine length-weight relationships of T. palustris in conserved and un

conserved mangroves forest of Michamvi village.

1.4 Research Hypotheses

The hypotheses of this research are:

The abundance of T. palustris species is significantly greater in conserved

mangroves than unconserved mangroves.

There are significant differences in size frequency distribution of T.

palustris in conserved and unconserved mangrove forest.

There is a significant difference in length-weight relationship of T.

palustris found conserved and unconserved mangrove forest.

1.5 Significance of the Study

The results obtained from this study will benefit the scientific community and

conservationist to get preliminary data which shows the importance of mangrove

conservation that can help to conserve T. palustris. The study will also enhance the

understanding of the status of T. palustris in Zanzibar, which is currently used as

food and as feed for crabs fattening projects. Because of the limited availability of

trash fish, the most common feed used by coastal communities are marine gastropods

(T. palustris). This information will benefit the government of Zanzibar on preparing

by-laws, regulation and guidelines to enhance focused management of mangrove to

sustain the gastropod resources.

6

1.6 Literature Review

1.6.1 Abundance

Juveniles and adults of T. palustris are usually present throughout the whole forest,

from the landward belt to the seaward fringe, locally reaching very high densities at

various levels. The T. palustris is widespread throughout the Indo-Pacific area and is

one of the most abundant inhabitants of mangroves, reaching remarkable densities in

some locations, e.g. 150 adults m2 in New Caledonia Plaziat, (1984) and

approximately 20 adults m2 in Kenya Fratini et al., (2004).

The study conducted by Akil and Jiddawi,(2001) in Jozani showed that Mollusca was

a dominant group in Jozani-Pete mangrove creek Zanzibar and the corn-like

gastropod T. palustris were represented by nearly four in every ten molluscan species

counted. An indication of a negative impact of sewage on T. palustris populations is

provided by a preliminary study on fauna distribution in the disturbed mangrove

system of Maruhubi, Zanzibar by Machiwa and Hallberg (1995). T. palustris proved

to be among the commonest mollusc species where Avicennia marina leaf litter was

present, except in areas where sewage disposal occurred.

T. palustris is known to be a surface-dwelling organism and due to its high

abundance and surface-dwelling behaviour, T. palustris is likely to have an impact

on the biotic and abiotic properties of the sediment surface layer of mangroves

Olafsson, (2003). This is by offering a link in nutrient cycling in mangrove

ecosystems Fratini et al., (2004). During the last decade, this most common and

abundant mangrove gastropods, T. palustris Linnaeus,(1767), has been the subject of

7

several ecological studies due to the significant quantities of leaf litter that it

consumes and processes, and it has become a recognized link in nutrient cycling in

mangrove forests Slim et al., (1997); Fratini et al., (2004). The study done by Blanco

et al (2012) also shows the decline of mangrove gastropods was related to physical

microhabitat ( e.g trees, prop roots and seedlings) degradation and alteration of soil

properties (e.g temperature, pH, organic matter content). Furthermore the collection

of these gastropods for feeding crabs reduce their abundance, Mirera, (2009).

1.6.2 Distribution

As they are such effective grazers and prefer areas under the canopy of mangrove

trees Crowe and McMahon, (1997) and muddy substrate to sandy substrate Rumbabu

et al., (1987), they may be important competitors with crabs in certain area within

mangroves Dahdouh-Guebas et al., (1998) and consume a considerable amount of

leaf litter Fratini et al., (2004). T. palustris distribution also depends on salinity, pH,

temperature and leaf litter accumulation Pape et al, (2008). T. palustris is a truly

amphibious species, active both at low and high tides Fratini et al., (2000, 2001).

However, this snail seems to avoid the driest landward and the most exposed

seaward zone of the mangrove forest, by clustering on the typically fine substrata of

the most shaded patches and in small tidal pools formed in between the aerial roots

of mangrove trees Houbrick, (1991); Slim et al., (1997).

1.6.3 Factors Affecting Distribution and Abundance

Recent years expansion of crab farming in many coastal villages has resulted in

increased pressure (overharvesting) on this species, the study done by Lamtane

8

H,Abdallah J.M,Lilungu J.A(2013).,in Pangani show the crab fattening activities

leads into low abundance and small sized T.palustris and C.decollata. Although mud

crab farming activity has the potential to contribute to communities food security

offering additional livelihoods, this feed input to the farmed crabs may compete with

the utilization of this resource as food for poor people. In Bagamoyo, Tanga,

Zanzibar and Rufiji area, the important crab species are Scylla serrata locally known

as Kaa koko or Mboga and Portunus pelagicus known as Kara Pemba Ngoile and

Shunula, (1992), Mgaya et al. (1999). Women and children collect T. palustris

(locally known as Suka or Tondo) for food and men collect it mainly as fish bait or to

be used as feed in the trial prawn aquaculture pond. Also the size frequency

distribution between adults and juveniles is affected by food availability since several

studies done on T. palustris explain on their size frequency distribution. T. palustris

is known to feed on both the detritus as juveniles and leaf litter as adults, and to

compete with sesarmid crabs, scylla serrata for these resources Fratini et al., (2000),

(2004); Pape et al., (2008).

1.6.4 Growth

The study done in Kenya measured growth of T. palustris by using shell length of

5cm for adult Fratini et al., (2004). However, the size class marking the transition

between the juvenile and the adult stage probably varies throughout the geographic

range of this species Houbrick, (1991). The growth stages of T. palustris can easily

be distinguished on the basis of shell morphology as maturity is indicated by a

thickening of the margins of the aperture, including the outer lip Houbrick, (1991);

9

Nishihira et al., (2002). Therefore it would have been more accurate to delineate age

groups based on the morphology of the shell.

1.6.5 Feeding Ecology

The gut-content analysis confirms that juveniles are detritivorous and adults are

mainly leaf-litter consumers Fratin et al., (2001). As widely recognized for many

gastropods Croll, (1983), T. palustris uses olfaction to locate suitable food resources.

In particular, in its food search it relies on chemical cues released by broken

(scraped) mangrove leaves or propagules, as experimentally demonstrated by Fratini

et al. (2001). This means that this snail is able to locate a mangrove leaf feeding

individuals due to the cues released by the leaves when grazed, while conversely it is

not attracted to snails that are not feeding nor to food items that have not been

scraped Fratini et al., (2001). T. palustris is the only leaf consumer capable of

searching for food under water during high tide and is responsible for the removal of

a great quantity of mangrove litter Slim et al., (1997). T. palustris is known to be

omnivorous, feeding on detritus, leaf litter, mangrove propagules, carrion, sediment

particles, benthic diatoms and bacteria Dahdouh-Guebas et al., (1998). Due to such

food preference the organisms are found in areas that are wet and also under canopy

of mangrove trees Crowe, (1997).

10

1.6.6 Ecological Role

Recently, it has become apparent that T. palustris (Potamididae: Gastropoda) is

crucial in the nutrient cycling process in mangrove forests as this species is

responsible for processing significant amount of leaf litter Slim et al., (1997); Fratini

et al., (2004). T. palustris play an important role in the food web, nutrient cycling

and overall energy-flux of mangrove ecosystems Kathiresan and Bingham, (2001).

11

CHAPTER TWO

MATERIALS AND METHODS

2.1 Description of the study area

The study was conducted at the Michamvi peninsula located in the Chwaka Bay on

the east coast of Unguja Island (main Island of Zanzibar).

2.1.1 Geographical location

Chwaka Bay (approx. 6013’00’’-02’54’’S and 39023’38’’-32’00’’E) is situated on the

east coast of Unguja Island, Zanzibar. The Bay is a major feature of the east coastline

of the Island with an area about 50km2. The Bay has an almost rectangular shape,

surrounded by an extensive arm protecting it from the open ocean on the east side.

Extensive vegetation surrounds the coasts; to the south mangrove forest dominate; to

the west coastal terrestrial vegetation as well as some mangroves are found; along the

eastern shores there are mainly sand dunes. The large mangrove stand to the south

which form part of the Jozani-Chwaka Bay National Park is divided by two main

creeks, namely Mapopwe in the west and Kinani in the east Tobisson et al, (1998)

12

Figure 2. 1: Map of Chwaka bay showing the study sites, Michamvi kae

(kibidukani) site 1 and Kinani site 2

2.12 Hydrology

Chwaka Bay is a shallow system on the east coast of Unguja Island, Zanzibar,

Tanzania. This embayment is an intertidal water body with an average depth of 3.2 m

and an estimated area of 50 km2 at high spring tide and 20 km2 at low spring tide

Cederlöf et al. (1995). The area contains all three critical marine habitats namely

13

mangroves, sea grasses and coral reefs, and is part of the Jozani Chwaka Bay

National Park. The mangrove forest of Chwaka Bay is the largest single area of

mangrove in Zanzibar.

2.13 Climate

There are two rainy seasons in Zanzibar: the extended rainy season that occurs

during the months of March, April and May, and the short rainy season which extend

from October to December McClanahan (1988). The region receives between 1000

mm and 1500 mm of rainfall per annum. Air temperatures are tropical and range

from 27-30°C. Predominantly north-easterly winds occur between October and

March, and mainly south-easterly winds from March to October.).

2.1.4 Social economic activities

Most of inhabitants of Chwaka Bay depend on some terrestrial but mainly marine

based activities for their subsistence. However this dependence varies from one

village to another depending on several factors such as closeness to the resources,

surrounding ecosystems, family traditions, the need for ready cash, and ease of

conducting the activity and alternative sources of income Ngazy (1997). Most people

in Chwaka bay area are involved in marine resources associated activities through

fishing, mangrove cutting and seaweed farming Mohammed and Jiddawi (1999). The

livelihood system is somehow complex since the inhabitants have to strategically

combine exploitation of resources from both marine and terrestrial ecosystems for

survival.

14

Table 2. 1: Distribution of main income generating activities in Chwaka Bay

area.

ACTIVITY PERCENTAGE

Fisher 36%

Farming/wood cutting 25%

Sea weed farming 15%

Gleaning 7%

Government employee 6%

Entrepreneur 6%

Others 3%

Hotel employee 2%

Live stock 0%

Source: Jiddawi, N.S., Personal interviews (unpublished

data), 2010. N=220

Table 2. 2: Main income generating activities by gender in the Chwaka Bay

area.

MEN

ACTIVITY PERCENTAGE

Fisher 72%

Farmer 20%

Other 8%

WOMEN

ACTIVITY PERCENTAGE

Seaweed farmer 80%

Invertebrate collector 14%

Other 6%

Source: Jiddawi. N. S., personal interviews (unpublished data), 2010.

2.2 Description of the study site.

The study was conducted at Michamvi Kae (the last village on the Chwaka Bay

village series) where according to the population census (2012) the total population

15

was 1,572 inhabitants, (895 males and 677 female). The study was conducted in two

sites. Site one is located at Kibidukani (the area where mangroves is conserved by

community based conservation programme) and is 700m in width and 1000m in

length. The second site is kinani (the long narrow forest surrounded three villages

Michamvi,Bwejuu and Ukongoroni) , this area villagers clear Mangroves for their

livelihood. These two areas are about 3km apart.

2.2.1 Conserved mangrove forest at Michamvi

Mangrove conservation programe was established in 2000 in Michamvi kae

mangrove forest, when the local community recognize the over harvesting of

mangrove forest, for social and economic activities such as for fuel and timber

Mohammed (2004). This programe was an intervention measure to avoid several

problems such as rising of water level near to the people settlement and reduction of

number of animals live in mangrove forest.

Additionally the communities were encouraged to conserve the mangrove forest by

the benefits they were getting. Like the rest of Chwaka bay this forest contains all ten

species of mangrove occuring in Zanzibar dominated by species is R. mucronata,

followed by B.gymnorrhiza ,C.tagal, A.marina S.alba. and other five species are

Xylocarpus granatum, X.moluccensis, Heritiera littoralis ,Lumnitzera racemosa and

Pemphis acidula Shunula et al (2001); Shunula (2002) present in small amount.

The community leadership was responsible for the management of this forest at

Kibidukani area in Michamvi kae. However the control of these conserved areas is

16

not effective due to the problems of poachers who enter in the forest and collect

some invertebrates including T.palustris.

Plate 2. 1: The conserved mangrove forest at Michamvi village, the area

known Kibidukani mangrove forest. (Field photo).

2.2.2 Unconserved mangrove forest at kinani

This is very large area of mangrove forest surrounding three villages Michamvi,

Bwejuu and Ukongoroni, where people clear mangrove for their livelihood.

As in other parts of the world the mangroves of Zanzibar are threatened by

destruction intimately linked with human activities, such as logging for timber and

cutting for fuel wood (Mkomwa, (1992); Shunula and Whittick, (1996); Semesi,

(1998). The same case of Kinani mangrove forest neither community leadership nor

government care about this forest, this leads into loss of resources which have very

high economic value. In Zanzibar, mangrove ecosystem is located on a strategically

17

economic zone for tourism industry which contributes 22% of GDP and about 80%

of government revenues OCGS, (2007). Healthy ecological system with high

biological diversity could provide great opportunity for development of eco-tourism

industry that helps in conserving and sustainable utilization of the forest resources

Mchenga & Rashid, (2010).

Plate 2. 2: Unconserved mangrove forest at Kinani mangrove forest

Michamvi, Zanzibar with fallen logs and young mangrove plants.

(Field photo)

2.3 Data collection

2.3.1 Sampling for T.palustris

The T. palustris was sampled through three transect line of 175m, at interval of 30m

apart from one transect line to another in each site. The sampling was conducted in

seven plots of (5m x 5m) at interval of 20m from one plot to another in each transect

line, the transect lines were from the shore to the sea in both un conserved and

18

conserved forest. T. palustris was collected at the centre of each plot by quadrat of

(1mx1m), over the soil and roots of mangroves by hand. The sampling was

conducted once a week for two months January and February 2014 in both sites. The

data was collected during low spring tide when the T.palustris was observed in their

habitats. The collected samples were preserved in a refrigerator for later analysis.

The length of T.palustris was measured by Vernier calipers and its weight was

measured by Electrical balance.

Plate 2. 3: T. palustris in the field, most of the time occurs in a cluster

2.3.2 Sampling of the soil

About 10 grams of soil in each quadrat of 1mx1m was sampled, then dried in the

laboratory by putting in dry container and put in the oven at about 600C for 72hrs,

after which the original dry weight was measured. Then soil sample was transferred

in a crucible and burned in a Muffle furnace at about 4500C for about 20hrs, the final

19

weight was measured. The loss on ignition (LOI) was measured and the organic

content expressed as a percentage of the dry weight ,Heiri et al.,( 2001). The organic

matter of the soil was obtained by the following formula:-

Organic matter = original dry weight of the soil-final weight of the

soil X 100

Original dry weight of the soil

2.3.3 Sampling of sea water

About 100ml of sea water in each quadrat of 1mx1m was sampled and stored in the

bottle to the laboratory to measure pH, by using pH meter. The pH value of each

quadrat was obtained except in a dry quadrat (no water sample obtained).

2.3.4 Measurement of salinity and temperature

The salinity of sea water was measured in each transect line by using Salinometer, in

both sites. While some biogeochemistry parameters are known to be relatively

constant throughout the year, or oscillate seasonally or with important events (e.g.,

heavy rains or winds), some fluctuate significantly during a single tidal cycle (e.g.,

temperature, salinity) Chapman and Tolhurst, (2007). Temperature was measured in

each transect line by using Thermometer.

2.4 Data analysis

Abundance of T. palustris was obtained by counting the total number of individuals

at given site. Abundance of all T. palustris in site 1 and 2 was obtained by summation

of total number of individuals in each site. The coefficient of variance in two sample

t-test was obtained by using Paleontological Statistics Software Package for

20

Education and Data analysis (PAST) and was used to compare levels of significance

difference in mean abundance between two sites.

The size frequency distribution was obtained by classifying individual into two

groups of adult and juvenile according to their length, those reaching 5cm and above

in length are adults and those less than 5cm in length are juveniles, Fratin et al.,

(2004). The size frequency distribution was calculated by 2x2 contingency table .Chi

square test of association was used to determine the significance of variation in size

frequency distribution.

The length weight relationship of T.palustris was obtained by simple Linear

Regression in each site.

The significant difference in length as well as weight of T.palustris from the two sites

was obtained by Mann-Whitney test and the weight length relationship of T.palustris

between conserved and unconserved mangrove forests was obtained by using student

t-test.

21

CHAPTER THREE

RESULTS

3.1 Abundance of Terebralia. palustris in conserved and unconserved

mangrove forest

A total number of T. palustris obtained from this study was 635 individuals. Both

sites had approximately the same mean number of T. palustris (t 0.05 (40) = 0.1025; P =

0.9188) though the conserved forest had slightly higher total number of individuals

than unconserved.

The mean abundance of the T. palustris in the conserved mangrove was 15.3 ±2.751

individuals per quadrat whereas in unconserved forest was 14.9 ±1.733 individuals

per quadrat (Figure3.1).

Figure 3. 1: Mean abundance of T. palustris (Mean±SE) in conserved (site 1)

and un conserved mangrove forest (site 2)

22

With respect to transects in conserved and unconserved mangrove forests, there was

very slight variations in mean abundance of T. palustris among transects, with the

first transect in each forest having highest mean abundance per quadrat (Figure 3.2).

Figure 3. 2: Mean abundance of T. palustris in transects of conserved and

unconserved mangrove forests of Michamvi village, Zanzibar

3.2 The size frequency distribution of T. palustris in conserved and

unconserved mangrove forests

The size frequency distribution (obtained by classifying individuals of T. palustris

according to their lengths) resulted in having adults and juveniles (section 2.3.1).

There was significant difference in size frequency distribution between the conserved

and unconserved mangrove forest (Chi-Square test: 20.05 (1) = 28.679; P = 0.001).

The frequency of adults was higher in unconserved than conserved mangrove forests

while the number of juveniles was higher in conserved than in unconserved

23

mangrove forest (Figure 3.3). In the whole study sites the size frequency distribution

of adults was significantly higher than that of juveniles (Chi-Square test: 20.05 (1) =

478.112; P ˂ 0.0001).

Figure 3. 3: Size frequency distributions of adults and juveniles between

conserved and unconserved mangrove forests of Michamvi

village, Zanzibar (FSG = Frequencies of size groups of T. palustris)

3.3 Length and weight of T. palustris in the conserved and unconserved

mangrove forests.

3.3.1 Length weight relationships of T. palustris in conserved and unconserved

mangrove forests

Simple linear regression showed positive significant relationship between length and

weight in T. palustris both in conserved mangrove forest (t 0.05(317) = 53.804; P ˂

0.05) (Figure 3.4) and in unconserved forest (t 0.05(309) = 32.347; P ˂ 0.05) (Figure

3.3.2). This meant that length (independent variable) influenced the weight in such a

way that when length increases the weight also increases (Figures 3.4 and 3.5). When

24

the slopes of populations in the two forests were compared, significant positive

relationships between length and weight of T. palustris was found (t 0.05 (626) =3.2268;

P = 0.00132) meaning that the two sites had different populations.

.

Figure 3. 4: The length weight relationship of T.palustris in conserved

mangrove forest.

Figure 3. 5: The length weight relationship of T. palustris in unconserved

mangrove forest.

25

3.4 Variations in length and weight of T. palustris between conserved and

unconserved mangrove forests.

Lengths of T. palustris individuals were significantly different between conserved

and unconserved mangrove forest (U0.05(318,310) = 2789; P ˂ 0.001). Individuals of T.

palustris in uconserved forest had longer lengths (7.6 ± 0.054 cm) than individuals in

conserved forest (6.7± 0.078 cm). The individuals of T. palustris were significantly

heavier in unconserved forest (28.2 ± 0.494 g) than in conserved forest (21.2 ± 0.734

g ) (U0.05(318,310) = 2933; P = P ˂ 0.001 ). The larger values of mean lengths and

weights of T. palustris in unconserved forest than conserved forest were due to

presence of large number (frequency) of adults in unconserved forest (see section

3.2).

26

CHAPTER FOUR

DISCUSSION

4.1 Impact of mangrove destruction on abundance of T. palustris

Mangroves destruction is a big problem around the world, this including clearance of

mangroves and use for waste disposal; this affects mass of mangroves dwellers and

leads into loss of aquatic biodiversity. This problem is rapidly increasing due to

increase of population, poverty, lack of education and awareness among the coastal

people. Destruction of mangrove forests is occurring globally. Global changes such

as an increased sea level may affect mangroves Ellison (1993), Field (1995), More

important, it is human alterations created by conversion of mangroves to mariculture,

agriculture, and urbanization, as well as forestry uses and the effects of warfare, that

have led to the remarkable recent losses of mangrove habitats Marshall (1994),

Primavera (1995), Twilley (1998).

The abundance of T. palustris seen like not affected by mangrove destruction in the

present study since the results show their abundance in conserved mangrove forest

does not vary significantly with the abundance in unconserved mangrove forest.

However previous studies show the major threats of T. palustris in the world is

habitat destruction and alteration which include mangrove destruction and waste

disposal. Machiwa and Hallberg, (1995).

The mudwhelk T. palustris Linnaeus, (1767) is a key epifaunal species in East

African mangrove forests. Studies have shown that it is important for the nutrient

cycling by consuming large amounts of Avicennia marina (Forsk.) and Rhizophora

27

mucronata Lam litter, it can also regulate microphytobenthic primary productivity

through feeding and crawling activities Cannicci et al., (2008); Lee, (2008).

However, this species disappeared completely following organic contamination of

mangrove areas in Mozambique, Kenya and Zanzibar (Cannicci et al., in press)

suggesting an upper tolerance limit to the conditions present in those areas. Even

there is no organic contamination in Michamvi mangrove forest but the waste

disposal from the village and tourist house also may leads into decrease abundance

of T. palustris gradually and lastly disappeared of this gastropods species.

The abundance of T. palustris does not vary significantly between conserved

mangrove forest and unconserved mangrove forest may be caused by small size of

the mangrove forest in which this study was conducted as well the closeness of the

sites (site one and two) and the short period in which the study was conducted. The

present study proposes the future study on abundance of T. palustris to be done for

relatively long period, in large areas and farther distance between the sites.

The study done by Blanco et al (2012) at Uraba Gulf, Caribbean coast of Colombia,

the gastropods Neritina virginea in mangroves are local extinct due to clear cutting,

may exert strong negative effects on the ecosystem function because it is dominant

omnivore, this show gastropods in mangroves affected by destruction of their habitat,

therefore even T.palustris will be locally extinct if the mangrove destruction will

continue in Michamvi Zanzibar.

28

The studies done in various mangrove ecosystems around the world show that

abundance of T. palustris or other mangroves invertebrates are favored by shading

effect of the mangrove forest and leaf litter accumulation, these factors are present in

Michamvi mangrove forest. Frith et al. (1976) found that the presence of mangrove

trees and associated microhabitats accounted for the high abundance of grapsid

crabs, but unfortunately the abundance of T. palustris in the present study are lower

than expected; this may be caused by the following reasons:

Firstly the overharvesting of these gastropods done by women and children of

Michamvi and neighboring villages like Bwejuu for home consumption or selling in

local market (personal observation), affects the abundance of T. palustris in both

conserved and non conserved mangrove forest of Michamvi Zanzibar. However the

overharvesting occur extremely in unconserved mangrove forest because the T.

palustris become more exposed after clearing of the Mangroves and also in this

forest there is no restriction on harvesting both mangroves and T. palustris compared

to conserved mangrove forest. Furthermore the poachers are a big problem for

reducing the T. palustris abundance in conserved mangrove forest. Overharvesting is

among the major threats which leads into loss of biodiversity and sometimes cause

local extinction of the species.

Also T. palustris have a tendency of migrating from exposed region to the mangrove

forest for searching food and shelter , Crowe and McMahon, (1997) so this causes to

become more abundant in the interior part of the forest where is difficult to reach for

sampling.

29

Secondly both mangrove forests are dominated by R. mucronata which may cause

reduction in abundance of T. palustris. A study done by Semesi et al., 1998 at

Mangrove of Bagamoyo District shows that T. palustris tends to concentrate in

substrates with high amounts of decomposing leaf litter of Avicennia marina

mangroves. The overall abundance of T. palustris is lower in the two sites; this may

be caused by the A. marina present in small quantity. The study done by Fratin et al

(2008) at Dabaso shore, Kenya reports that this snail (T. palustris) is differentially

attracted to different mangrove species: the major attractive power is wielded by the

rhizophoracean species and Pemphis acidula, while X. granatum does not attract this

snail at all. Therefore the abundance of T. palustris is due to various mangrove

species available in the specific area; they make some adaptation on the species of

mangroves occurring in the area since the above studies conducted in different area

provide different results. However Blackburn (1999) has pointed out that the

abundance of different species is not equal in an area.

4.2 The size frequency distribution of T.palustris in Conserved and

Unconserved mangrove forest

T. palustris use different types of food between adults and juveniles; this may cause

varied distribution in both sites. There are several studies that have been done and

reported the distribution of T. palustris to be affected by the type of food consumed

according to their size. A spatial separation between young and older individuals was

observed by Soemodihardjo and Kastoro (1977).

30

Furthermore, environmental variables were within the optimum range for better

growth and distribution of macro fauna within the mangrove forest, Lamtane

H,Abdallah J.M,Lilungulu J.A(2013). Also most of the time the harvesters take

adults, well grown T.palustris, so this affects the actual number of adults in the sites.

Due to anatomical differences in the structure of the radula, only large (shell height>

5 cm) T. palustris actively feed on fallen mangrove leaves, propagules and fruits,

while small individuals (shell height< 5 cm) are usually detritivorous or deposit

feeders Nishihira, (1983); Houbrik, (1991); Slim et al., (1997); Dahdouh-Guebas et

al., (1998); Fratini et al., (2004); Pape et al., (2008). This different feeding strategy

has been used to explain the spatial segregation between juveniles (more common in

tidal channels and pools) and adults (common in the forest) reported by various

authors for Jakarta Soemodihardjo and Kastoro, (1977), Western Australia (Wells,

(1980) and Gazi Bay, Kenya Slim et al., (1997); Pape et al., (2008). This reason may

cause reduction in the number of juveniles, because sampling was done under

mangrove trees where leaf litter accumulation was most abundant and not in tidal

channel, pools or substratum; most of the time the transects fell in mangrove forest

even there are relatively low destruction in unconserved mangrove forest. However

the juveniles collected were approaching to adults size; this may be due to their

sharing type of the food with adults.

31

4.3 The length weight relationships of T.palustris in conserved and

unconserved mangrove forest

The relationship of weight and length in the present study correlates most of the

time, but sometimes it happen the T .palustris of the same length have different

weight. This may be caused by environmental factors such as availability of food

and shade of the mangrove forest. When T. palustris lives in area where food

availability are minimized for example no leaf litter accumulation and no shade of

mangrove trees direct sun light affect their growth , (example in area called Mbatani

at Michamvi mangrove forest),and the area near the sea rock no mangrove trees (all

mangroves are already cleared); there are T. palustris which stay there for long time

and does not grow anymore and are not used for human consumption because their

meat have changed and become bitter taste (researcher personal interview with

villagers).

Moreover the growth of the T. palustris is reduced due to mangrove destruction;

earlier people who harvested this gastropods for home consumption reported that

T.palustris was large and heavy because they got enough food, shelter and other

suitable environmental factors like salinity and temperature but those factors are

minimized and affected by clearing of mangroves and waste disposal which cause

retardation of growth of T. palustris . However the present study shows the length

and weight of T.palustris was high in unconserved mangrove forest than in

conserved, this may caused by environmental factors such as pH, salinity,

temperature and organic matter as well as the nearest of the study sites.

32

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

From the results obtained in this study the following conclusion can be drawn:

The abundance of T. palustris in conserved mangrove forest is higher compared to

that of unconserved mangrove forest; this shows that mangrove conservation

increases the abundance of T. palustris, mangrove forest is like an umbrella species,

its conservation leads into conservation of fauna that totally depends on mangroves

for their survival.

The abundance of T. palustris observed in this study is lower than expected because

there are various factors that affect their abundance such as clearing of mangroves,

waste disposal and overharvesting that leads to loss of aquatic biodiversity due to

habitat destruction and alteration and sometimes cause a local extinction of the

species.

The uneven distribution between adults and juveniles observed in the present study

may be due to different type of food consumed by these two different population,

short period of the study and nearness of the study sites.

The growth rate of T. palustris between conserved and unconserved forest is

different, T. palustris in conserved mangrove forest was small in size and low weight

while in unconserved mangrove forest T. palustris was longer in size and heavier that

could mean that adult/juvenile size may vary from site to site depending on the

33

ecological status of the environment especially over exploitation of the resource and

degradation of the habitat.

5.2 Recommendations

Based on the present study, the following recommendations are put forward:

Banning of clearing of mangroves and controlling disposal of waste is needed

in order to improve the values of mangrove forest of Michamvi village.

Mangrove restoration must be motivated among villagers in order to save the

aquatic flora and fauna of the Mangrove forest.

Moreover knowledge is needed for the villagers and in schools on the

importance of conserving of biodiversity and proper use natural resource for

future generations.

Future study is proposed to be conducted for long time in many sites of far

distance between one another in order to provide more information on impact

of mangrove conservation on abundance and growth of T.palustris or other

marine invertebrates in Michamvi mangrove forest.

The villages leadership can make contract with buyer on the unconserved

forest for the social obligation; in order to encourage villagers to stop on

destruction of the mangrove forest and instead restore the forest and get other

benefits from the buyer like building of their schools, hospitals or other social

services in the village, while buyer benefits from ecosystem services like

fishing or use the forest for tourism activities. This program called PES

(Payment for Ecosystem Services). On the other hand knowledge of

34

entrepreneurship must be provided to the villagers as alternative way to get

their income.

The effectiveness of Community Based Conservation (CBC) at Michamvi

Kae must be improved.

35

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APPENDICES

APPENDIX 1

ABUNDANCE OF T. Palustris ALONG THE THREE TRANSECTS LINES OF

CONSERVED MANGROVE FOREST

TRANSECT

QUADRAT

TRANSECT 1 TRANSECT 2 TRANSECT 3 TOTAL

1 2 18 18 38

2 1 16 8 25

3 37 5 11 53

4 42 22 1 65

5 28 17 1 46

6 6 8 30 44

7 4 13 33 50

TOTAL 120 99 102 321

MEAN

ABUNDANCE

17.14 14.14 14.57 49.9

43

APPENDIX 2

ABUNDANCE OF T.Palustris ALONG THREE TRANSECTS LINE OF

UNCONSERVED MANGROVE FOREST

TRANSECT

QUADRAT

TRANSECT 1 TRANSECT 2 TRANSECT 3 TOTAL

1 18 11 15 44

2 7 24 9 40

3 25 20 16 61

4 21 18 19 58

5 6 21 14 41

6 23 22 1 46

7 22 1 1 24

TOTAL 122 117 75 314

MEAN

ABUNDANCE

17.42

16.71

10.71

44.9

44

APPENDIX 3

THE ABUNDANCE OF T.Palustris IN BOTH CONSERVED AND

UNCONSERVED MANGROVE FOREST

quadrat no. Site 1 Site 2

1 2 18

2 1 7

3 37 25

4 42 21

5 28 6

6 6 23

7 4 22

8 18 11

9 16 24

10 5 20

11 22 18

12 17 21

13 8 22

14 13 1

15 18 15

16 8 9

17 11 16

18 1 19

19 1 14

20 30 1

21 33 1

TOTAL 321 314

MEAN 15.3 14.9

45

APPENDIX 4

THE PERCENTAGE OF ORGANIC MATTER CONTENT OF THE

SEDIMENTS IN SITE1 AND SITE 2

QUADRAT SITE 1 SITE 2

1 12.72% 5.73%

2 9.54% 5.45%

3 6.81% 8.53%

4 6.37% 10.88%

5 5.21% 17.70%

6 7.96% 8.36%

7 5.56% 7.87%

8 5.67% 10.34%

9 11.01% 9.46%

10 2.75% 5.19%

11 12.58% 7.09%

12 5.56% 4.93%

13 4.19% 5.19%

14 4.96% 5.57%

15 9.03% 3.72%

16 7.23% 7.36%

17 9.48% 9.18%

18 7.63% 7.36%

19 7.23% 8.30%

20 5.58% 6.85%

21 6.30% 7.34%