i

CERTIFICATION

The undersigned certifies that she has read and hereby recommends for acceptance by

the University of Dodoma dissertation entitled Anthropogenic Impacts on Mangrove

and their associated macrofauna in Wesha and Ngezi Pemba Islands, Tanzania in

fulfillment of the requirements for the degree of Master of Science in Biodiversity

Conservation of the University of Dodoma.

………………………………

Dr. Mariam Hamisi

(SUPERVISOR)

Date……………………………

ii

DECLARATION AND COPYRIGHT

I Amour Hamad Saleh, do here by declare that this dissertation is my own original

work and that it has not been presented and will not be presented to any other University

or other academic institution for a similar degree award.

Signature…………………………………

No part of this study may be reproduced, stored in any retrieval system or transmitted in

any form with out permission of the author or the University of Dodoma.

iii

ACKNOWLEDGEMENT

On top of each and every one, appreciation and honour is to ALLAH MASSIVE for

giving me the strength, tolerance and get-up-and-go to complete this dissertation.

However, a number of people contributed in one way or another to make this study

successful. I would like to mention some of them. It is my pleasure to express my

sincere thanks and gratitude to my supervisor Dr. Mariam Hamisi, who devoted her

time and energy to firmly and adeptly supervise this dissertation. Her guidance,

encouragement and constructive ideas throughout the entire research period made it

possible to successfully complete this report.

I would like to express my sincere appreciations to my family for granting me funds,

support and encouragement which assisted me to carry out this degree. Special thanks

go to Dr. Islam Salum of the first Vice President office Zanzibar for his constructive

criticism and support which shaped this work. I also thank the Ministry of Education

and Vocational Training of Zanzibar for grating me an opportunity for further study at

the University of Dodoma. Furthermore, I am gratefully indebted to my friend Abdalla

Rashid Ali for supporting me during whole period of data collection identification and

storage of samples.

I also wish to extent my sincere gratitude to the Ministry of Agriculture and Natural

resources Pemba for providing authority to conduct this study in both Wesha as well as

Ngezi natural forest reserve. Moreover I would like to thanks all Lecturers from the

department of Biological Science for encourage me for providing moral and challenges

during the class session.

iv

DEDICATION

This work is dedicated to:-

My parents

My wife

My children

v

ABSTRACT

Anthropogenic activity is a crucial problem mostly in coastal area and may affect

mangrove and their associated macrofauna. Anthropogenic impacts on mangrove and

their associated macrofauna were examined in Wesha (non protected) and Ngezi

(protected) mangrove forest along Pemba coast in Tanzania. Mangrove and macrofauna

characterization, physicochemical parameters and anthropogenic activities were

determined. Data were collected through field observation and measurements,

questionnaires, checklists and focus group discussion. Instart 3 Trial version and

Statistical Package for Social Sciece were used to analyze data. In this study 8 species

of mangrove were identified in Wesha as well as in Ngezi. The average species density

of mangrove trees per hector was 23,600 for Ngezi and 19,400 for Wesha, with

regeneration rate of 3.1 and 1.8 seedlings /m2 in Ngezi and Wesha, respectively. During

the study a total of 33 species from three classes (bivalves, gastropods and crustaceans

were identified. The results revealed that Ngezi has more species richness (n = 25)

compared to Wesha (n = 23), while Wesha observed to have high species diversity

index (H' = 2.0) than Ngezi (H' = 1.8). Cutting mangrove, over-fishing, oil spills and

salt production were observed to be the major anthropogenic factors that affect

mangroves and their associated macrofauna in Wesha, with exception to oil spills all the

other factors were also observed in Ngezi. The anthropogenic factors was significantly

higher in Wesha as compared to Ngezi (P > 0.0399, t = 0.000, Df = 3). Anthropogenic

activities can affect mangroves and their associated macrofauna as well as the

environmental condition. Therefore, much effort is needed to ensure that anthropogenic

activities have been reduced so as to improve ecosystem healthier.

Keywords: Mangroves, Macrofauna, Anthropogenic, Distribution and Abundance.

vi

TABLE OF CONTENTS

CERTIFICATION ............................................................................................................. i

DECLARATION AND COPYRIGHT ............................................................................ ii

ACKNOWLEDGEMENT ............................................................................................... iii

DEDICATION ................................................................................................................. iv

ABSTRACT ..................................................................................................................... v

TABLE OF CONTENTS ................................................................................................ vi

LIST OF TABLES ............................................................................................................ x

LIST OF FIGURES ......................................................................................................... xi

LIST OF PLATE ............................................................................................................ xii

LIST OF ACRONOMY ................................................................................................ xiii

CHAPTER ONE ............................................................................................................... 1

INTRODUCTION ............................................................................................................ 1

1.1 Background to research problem ................................................................................. 1

1.2 Statement of the problem ............................................................................................. 2

1.3 General Objective ........................................................................................................ 3

1.3.1 Specific objectives. .................................................................................................. 3

1.3.2 Hypotheses. .............................................................................................................. 4

1.4 Significance of the study ............................................................................................. 4

CHAPTER TWO .............................................................................................................. 5

LITERATURE REVIEW ................................................................................................. 5

2.1 Mangrove and associated macrofauna ......................................................................... 5

vii

2.2 Socio-economic importance of macrofauna ................................................................ 6

2.3 Environmental factors affecting the distribution of macrofauna ................................. 8

2.4 Threats of mangrove and their associated macrofauna .............................................. 10

2.5 Conceptual Framework .............................................................................................. 13

CHAPTER THREE ...................................................................................................... 15

METHODOLOGY ....................................................................................................... 15

3.1 Study area .................................................................................................................. 15

3.2 Population and Climate .............................................................................................. 16

3.3 Research design ......................................................................................................... 17

3.4 Sample Design and Sample Size. .............................................................................. 17

3.5 Data collection method .............................................................................................. 18

3.5.1 Primary Data. ......................................................................................................... 18

3.5.1.1 Preliminary Survey. ............................................................................................ 18

3.5.1.2 Fauna and mangrove characterization ................................................................ 18

3.5.1.3 Physicochemical parameters ............................................................................... 19

3.5.1.4 Assessment of anthropogenic activities .............................................................. 19

3.5.2 Materials used ........................................................................................................ 20

3.6 Data analysis .............................................................................................................. 20

3.7 Data validity and reliability ....................................................................................... 21

CHAPTER FOUR .......................................................................................................... 22

RESULTS AND DISCUSSION .................................................................................... 22

viii

4. 1 Objective one: To examine mangrove distribution and regeneration rate along the

study area. ............................................................................................................... 22

4.1.1 Mangrove zonation ................................................................................................ 22

4.1.2 Mangrove diversity ................................................................................................ 24

4.1.3 Mangrove species density ...................................................................................... 26

4.1.4 Mangrove regeneration rate ............................................................................... 30

4.1.5 Factors affecting mangrove regeneration .............................................................. 33

4.2 Objective two: To examine the distribution and abundance of macrofauna ............. 35

4.2.1 Distribution of Macrofauna ................................................................................... 36

4.2.2 Abundance of macrofauna ..................................................................................... 41

4.2.2.1 Crustacean (Crabs) .............................................................................................. 44

4.2.2.2 Gastropods .......................................................................................................... 46

4.2.2.3 Bivalves .............................................................................................................. 49

4.3 Objective three: To assess the association between environmental conditions

(salinity, temperature and pH) to the distribution of macrofauna. ......................... 54

4.3.1 Salinity ................................................................................................................... 54

4.3.2 Pore water pH ........................................................................................................ 57

4.3.3 Pore water temperature .......................................................................................... 58

4.4 Objective four: To investigate anthropogenic activities affecting the distribution and

abundance of macrofauna ....................................................................................... 61

4.4.1 Respondents profile ............................................................................................... 61

4.4.2 Anthropogenic activities ........................................................................................ 62

4.4.2.1 Clear cutting of mangroves ................................................................................. 63

4.4.2.2 Over-fishing and illegal fishing gears ................................................................. 66

ix

4.4.2.3 Oil spills .............................................................................................................. 68

4.4.2.4 Salt Production ..................................................................................................... 71

CHAPTER FIVE .......................................................................................................... 74

CONCLUSION AND RECOMMENDATIONS ........................................................... 74

5.1 Conclusion ................................................................................................................. 74

5.2 Recommendations ...................................................................................................... 75

5.3 Limitation of the study ............................................................................................... 76

5.4 Area for further study ................................................................................................ 76

REFERENCES ............................................................................................................... 78

APPENDEX I- QUESTIONNAIRE FOR LOCAL COMMUNITY ............................. 98

APPENDEX 11-CHEK LIST FOR GOVERNMENT OFFICERS ............................. 101

x

LIST OF TABLES

Table 1: Distribution of mangrove species in three zone of Ngezi and Wesha forest .... 23

Table 2: Mangrove species & and their percentage in Ngezi and Wesha. ..................... 24

Table 3: Regeneration rate per species in Ngezi and Wesha mangrove forest. .............. 33

Table 4: Distribution of macrofauna in the study sites (+ found, - not found) ............... 37

Table 5: Abundance of macrofauna species identified in Ngezi and Wesha.................. 42

Table 6: Percentage of tree dwelling animals in different heights in Ngezi and Wesha. 53

Table 7: Percentage of macrofauna per zone in Ngezi and Wesha mangrove forest. .... 56

Table 8: Respondent profile ............................................................................................ 62

Table 9: Percentage of anthropogenic factors in Wesha and Ngezi ............................... 63

xi

LIST OF FIGURES

Figure 1: Conceptual Framework on anthropogenic impacts on mangrove and their

associated macrofauna .................................................................................................... 14

Figure 2: Map of Pemba Island showing the study areas (Modified by Bentje, 1990) .. 16

Figure 3: The mangrove species diversity in three zones of Ngezi and Wesha. ............ 26

Figure 4: Mangrove species density in Ngezi and Wesha mangrove forest. .................. 27

Figure 5: Number of mangroves trees per zone in Ngezi and Wesha. ........................... 29

Figure 6: Regeneration rate per zone in Ngeazi and Wesha mangrove forest. ............... 32

Figure 7: Diversity index (H') of macrofauna in three zones of Ngezi and Wesha ........ 41

Figure 8: Number of crabs per zone in Ngezi and Wesha mangrove forest ................... 45

Figure 9: Number of gastropods per zone in Ngezi and Wesha mangrove forest. ......... 48

Figure 10: Showing number of bivalves per zone in Ngezi and Wesha. ........................ 51

Figure 11: Variation of salinity in Ngezi and Wesha mangrove forest. ......................... 55

Figure 12: Variation of pH per zone in Ngezi and Wesha mangrove forest. ................. 58

Figure 13: Variation of temperature per zone in Ngezi and Wesha mangrove forest. ... 60

Figure 14: Common anthropogenic factors in Ngezi and Wesha mangrove forests ...... 71

xii

LIST OF PLATE

Plate 1: Determination of physico-chemical parameters of pore water in Ngezi forest . 19

Plate 2: Dead mangroves and planting of seedlings near the power plant at Wesha. ..... 30

Plate 3: Showing Wesha port where storage tanks of petroleum are located ................. 35

Plate 4: Showing (bivalve) Isognomon ephippium attached to the mangrove trunks ..... 52

Plate 5: Local peoples in utilization of mangrove trees for boat making along Wesha . 65

Plate 6: Crude oil generated by power plant along Wesha costal area. .......................... 69

Plate 7: Showing dead mangroves near the power plant at Wesha coastal area. ............ 70

.

xiii

LIST OF ACRONOMY

D O Dissolved oxygen

C B Community base conservation

PAH Poly aromatic hydrocarbons

RGoZ Revolutionary Government of Zanzibar.

1

CHAPTER ONE

INTRODUCTION

1.1 Background to research problem

Mangroves are evergreen salt tolerant plants found in tropical and sub-tropical

countries (Kathiresan, 2010). Mangroves play a crucial part in coastal tropical

biodiversity. First and for most, they provide a habitats, breeding site and feeding area

for many species of animals including macrofauna (Gilman et al., 2009, Donato et al.,

2011). Macrofauna/macrobenthos are organisms that live in or on sediment or attached

to hard substrates (Ogbogu, 2001). Benthic invertebrates are a vital component of the

estuarine food web, providing key linkages between primary producers and higher

trophic levels. Some are important economically; others improve water quality by

filtering the water or mediating nutrients remineralization within the sediment. Some

benthic invertebrates promote nutrients recycling or aerate the sediment, thereby

modifying the actual structure of the sediment, which in turn influences geochemical

processes within their habitat. Benthic species are even important in distributing food

resources (Nordhaus et al., 2009).

Another important role of mangrove ecosystem include pollutants filtering,

stabilization of coastal area through sediment trapping. Moreover, mangrove

ecosystem protects coastal area against storm damage (Semesi, 1998). Although

mangroves play significant roles but still they have been impacted through natural

factors as well as anthropogenic activities. In Zanzibar particularly Wesha, mangrove

are seriously impacted by human population pressure through harvesting of timber,

construction materials, wood fuel, sea weed farming and lime production. This

2

situation result ecological damage in such away biological diversity particularly

macrofauna are threatening through habitat destruction and fragmentation.

Apart from that, mangroves are also threatened by oil spills pollution and crude oil

generated by power plant. Oil spillage heavily contaminates marine shorelines, causing

severe localized ecological damage to the near shore community (Dauvin, 2000). So

the life in this region increasingly becoming unbearable due to the ugly effects of oil

spills and many communities continue to grown under the degraded impact of spill

(Gesteira, 2000). Oil spills involve the release of dangerous hydrocarbons such as

benzene and Polynuclic Aromatic Hydrocarbons (PAH) into the soil and water sources.

These spillages affect vast stretches of land and waterways thus polluting not only

crops but also the distribution of marine life (Ewa-oboho, 1994). However, physico-

chemical properties such as salinity, temperature, sediments, dissolved oxygen and pH,

have been reported to affect the distribution of these marine life (Ansa, 2005).

Oil and chemical pollution has been reported in various districts of both Unguja and

Pemba (ICMZ, 2009). The great concern is also Wesha, Chake Chake district in Pemba

where major petroleum storage facilities are located. The present study will focus to

assess the impacts of anthropogenic activities including oil spills pollution on

mangrove and its associated macrofauna, in Wesha mangrove forest Pemba.

1.2 Statement of the problem

Anthropogenic activities are the potential threats that may have considerable impacts

along Wesha mangrove forest and to their associated macrofauna. This is due to the

fact that, number of activities such as cutting mangrove, salt production and over-

3

fishing are conducted by the local community and large numbers of mangrove have

been impacted.

Hence, the magnitude of anthropogenic activities including oil pollution on mangrove

and their associated macrofauna along the coastal area of Zanzibar is not well

understood. Some studies have been conducted on marine coastal areas including

social- ecological resilience of mangrove (Othman, 2005), mangrove and crabs

ecosystem engineers (Nicholson, 2009). But, there is no adequate information about

anthropogenic impacts on mangroves and their associated macrofauna to the study

area. Therefore comprehensive scientific study of anthropogenic impacts on mangrove

and its associated macrofauna is needed so as to generate information for proper

protection and good management of coastal resources in Pemba mangrove forest and to

fill the existence knowledge gap.

1.3 General Objective

The general objective of this study was to examine the anthropogenic impacts on

mangroves and their associated macrofauna along selected Pemba mangrove forests.

1.3.1 Specific objectives.

i. To examine mangrove distribution and regeneration rate in Ngezi and Wesha

mangrove forests.

ii. To examine the distribution and abundance of macrofauna in mangrove forest

of Wesha and Ngezi natural forest in relation to anthropogenic sources.

iii. To assess the association between environmental conditions (salinity,

temperature and pH) to the distribution of macrofauna along the study areas.

4

iv. To investigate anthropogenic activities affecting the distribution and abundance

of macrofauna along the study areas.

1.3.2 Hypotheses.

i. There is higher distribution of mangroves and regeneration rate in Ngezi than

Wesha.

ii. There is higher distribution and abundance of macrofauna in Ngezi than Wesha

mangrove forest.

iii. There is possible relationship between environmental conditions (salinity,

temperature and pH) and distribution of macrofauna along the study areas.

iv. Higher anthropogenic activities affect negatively the distribution and

abundance of macrofauna in Wesha than Ngezi.

1.4 Significance of the study

The results of the present study will provide basic information about the impacts of

anthropogenic activities to the mangrove and their associated macrofauna which will

be useful for managers and policy makers. Apart from that, the recommendations given

by the study will be used to provide appropriate measures to be taken so as to minimize

anthropogenic factors that could affect coastal resources not only in Wesha but also in

other areas having similar problems. Moreover, the recommendations given by the

study will be also used to sensitize local community living around the coast, the

importance of sustainable use of coastal resources.

5

CHAPTER TWO

LITERATURE REVIEW

2.1 Mangrove and associated macrofauna

Mangroves are among the most important of coastal habitats because of their unique

ecological functions and services and their socio-economic value to local communities

and nations. Coastal ecosystems are resilient habitats because of their high functional

diversity and coastal communities are socially and economically resilient because of

the robustness of the ecosystem upon which they depend through the availability of

diverse economic activities (Adger, 1997).

Mangroves provide habitat for attachment for several animals including macrofauna.

Macrofauna/ macrobenthos are organisms that live in or on sediment or attached to

hard substrates (Ogbogu, 2001). They form a major link in the food chain as most

estuarine fishes, birds and mammals depends directly or indirectly on benthos for their

food supply and they are usefully bio-indicators because of providing a more accurate

understanding of changing aquatic condition than chemical and micro-biological data,

which at least give short term fluctuation (Ikomi et al., 2005). Through burrowing

activities benthic invertebrates have pronounced effect on sediment and biochemical

properties. They enhance the porosity of water flow through the sediment and assist in

flushing away toxic substances (Lee, 1998). Crabs are the most abundant of mangrove

macrofauna and are a valuable asset to the mangrove ecosystem. Burrowing crabs are

particularly important and may be ought to be considered ecological engineer as well

as aerate the sediment through burrowing (Jones et al., 1994). They reduce pore water

salinity by allowing flushing of the sediment via their burrows and also they trap

energy within the mangrove forest (Robertson, 1996; Lee, 1999).

6

Burrowing crabs create microhabitat for other fauna and also important in contributing

secondary production and increase the amount of nutrients and decrease the sulfide

concentration in the sediment due to their burrowing activities (Smith et al., 1991).

Macrofauna such as crustaceans that feed on a vast number of other animals in the

marine ecosystem are important links between producers and large consumers in

aquatic food webs (GAFRD, 2006). Krill and copepods are extremely abundant in the

worlds oceans may be the animals with the greatest biomass on the planet so, without

crustaceans, animal populations in aquatic ecosystems would collapse (Jones et al.,

1994).

Some macrofauna act as a key stone species for example mangrove crabs, that play a

critical role in maintaining the structure of an ecological community and whose impact

on community is greater than would be expected (Power et al., 1996). Also they have

significant impact on the bioturbation of the habitat and on nutrients recycling within

the system (Smith et al., 1991; Lee, 1998). It follows that key stone dependent

combines are perhaps more vulnerable and potentially unstable than communities

where key stone are absent (Navarrete & Menge, 1996). The reviewed literature

indicate that, there is a strong relationship between the mangroves and macrofauna

living in this ecosystem, so, this study will emphasize proper ways of conserving these

unique ecosystem that support large number of macrofauna which play an important

role in supporting local community in their livelihood needs worldwide.

2.2 Socio-economic importance of macrofauna

Macrofauna are among the major resources found in mangrove forest. These resources

have both socio and economic importance to the local communities living near the

7

coastal area as well as to those living away from the coast. They are very important in

supporting the livelihood to the respective Communities (Benabo et al., 1999). Most

people around the coastal areas rely on macrofauna such as crabs, lobsters, crayfish

and shrimps as a food which are mainly chief source of protein for people of low

income (Vijayalakshmi et al., 1993). According to Alfred et al., (1997), in Asia more

than ten million tons of Crustaceans are harvested for food each year. Crustaceans and

mollusks are two common invertebrate groups which are exploited by aborigines as a

food source (Kathirvel, 1992). Most of the hunting in the mangroves for those animals

is done by women, often with children in tow (Kathirvel, 1992). The mud crabs which

are an important food source and is eagerly hunted using sticks to extract the crabs

from their hole (Alfred et al., 1997).

The annual economic value of mangrove macrofauna estimated by the cost of the

products and services they provide. For example in Indonesia the cost of products and

services they produce has been estimated to be $200,000 - $900,000 /hectare (Wells et

al., 2006). The income is derived from the collection of the mollusks, crustaceans, and

fish that live in mangrove ecosystem (McLeod, 2006). This situation corresponds to

Tanzania whereby the collection of sea cucumber is significance source of cash income

for coastal communities; especially in rural areas on solid them at the local market

(Semesi et al., 1998; Canand, 1997a) reported that for the period of three months,

Tanzania export 73.8 metric tones of beche-de-mer (Sea cucumber) worth H K$

1,679,000 to Hong Kong. The total annual world catch is around 120,000 tones (wet

weight). According to Canand, (1997 b), Hong Kong is the largest world market for

these resources followed by Singer pore and Taiwan.

8

Besides their role in human diet, benthos especially mussels and clams are also used as

an important sentinel organisms for pollution monitoring studies and are being used as

indicators of pollution (Coccioni, 2000). The main reason of choice of benthic

organisms for pollution monitoring is that, they have the ability to bio-accumulate

many pollutants like heavy metals, hydrocarbons and pesticides (Gesteira and Dauvin,

2000). Their ability to metabolize pollutant is very low, so it is easy to measure the

body load of pollutants and also the amount that is depurated (Ajao and Fagade, 1990).

They are tolerant to wide ranges of temperature and salinity, and can be easily grown

in captivity for experimental studies. Moreover, these animals can be easily sampled

from inshore areas due to their sedentary habit (Ajao and Fagade, 1990). Different

studies conducted in various parts of the world shows that macrofauna are used as a

food for most people living near the coastal area and also as a source of income.

Therefore this study will promote different measures to be taken so as to avoid

improper use of these valuable resources in order to make them more sustainable since

they are still needed for future generation.

2.3 Environmental factors affecting the distribution of macrofauna

The distribution and relative abundance of macrofauna is not uniform, it depends upon

the physico-chemical properties (Odiete, 1999). Aggregations may occur at scales from

a few millimeters to many kilometers. Differences in physico-chemical properties such

as temperature, depth, pH, mean grain size, water currents, salinity, food and oxygen

tension are known to be associated with differences in density of marine benthic

populations between localities (Gibson, 1982).

9

Salinity and moisture or pore water content in mangrove ecosystem vary much

between seasons and on a diel basis as a result of dilutions during rainfall and day-time

evaporation (Kathiresan, 2006). The condition is accompanied by high temperature

variations during ebb and in windy conditions (Jansson, 1994). It has been reported

that, fresh water runoff has also been found to influence other environmental

parameters like temperature and it lowers the salinity and thus increase stratification,

which may affect the primary production (Nyandwi and Dubi, 2001). Such

environmental changes could have negative effects on the biodiversity of the coastal

zone if they persist for a long time. Further study show that the distribution of the

mollusks were found to be relatively high in area with high saline compared to the

other areas recorded with low salinity (Ajao and Fagade, 2002).

Changes in temperature have been found to influence the metabolism and can alter

ecological processes such as productivity and species interactions (Kennedy et al.,

2002). Species are adapted to specific ranges of temperature and salinity and are

therefore sensitive to just a few degrees higher or lower than those they usually

experience. Muthiah, (2005) found that larvae of sea cucumbers have the highest

survivorship and growth rate at specific water temperature of 28°C – 32°C.

Temperature influences organism’s biology including mortality, reproduction, growth

and behavior. For example, development of eggs and gonads in most of the marine

species are influenced by temperature (Lin et al., 2005).

Crabs concentration varies in the forest depending on the level of moisture, detritus

and shade. At low tide, crabs tend to concentrate in soggy areas and under shade

especially those species which occupy the upper intertidal areas such as Sesarma

10

species. In the lower intertidal areas the mangrove stems and roots carry a higher

biomass of barnacles, oysters and algae than those on the landward zone (Semesi et al.,

1998). This is due to less exposure to the air and the higher moisture content which

reduces the rate of desiccation (Semesi et al., 1998). Further study conducted by

Vilardy and Polania (2002), show that, the diversity of the mulluscs communities is

higher and species richness increases with low variation of dissolved oxygen. The

variation of physico-chemical parameters can affect the distribution and abundance of

macrofauna in their localities. The variation of physicochemical properties, may be

influenced by human activities that indirect affect the distribution of macro fauna at

large extent. Therefore different measures should be taken so as to minimize those

activities that may affect physico-chemical parameters which are very important in

regulating the distribution of mangrove fauna.

2.4 Threats of mangrove and their associated macrofauna

Mangrove vegetation play an important role in maintaining environmental complexity

and influencing the diversity and distribution of animals related to the ecological

system (Gao et al., 2005). At the same time these animals (macrofauna) play an

important part in mangrove ecological systems. They are both consumers and transfer

of energy flow and materials circulation system. However due to human population

pressure that rely on these resources to a large extent, hence they are seriously

threatened. Mangroves and their associated macrofauna are under threats Worldwide

through human population pressure (Maclaren &Masden, 2010). Currently these

resources are experiencing a high degree of degradation through a combination of

natural and human disturbance. However human factors contribute much (Fondo &

Marterns, 1998). It has been reported that cutting mangroves for building purposes,

11

fuel wood consumption, lime and charcoal making are the major threats of these

mangrove ecosystem (Semesi, 1999). The destruction of mangrove areas reduces the

diversity of macrofauna communities (Fondo & Marterns, 1998).

Over-fishing and the use of illegal fishing gears also have been reported to affect

population density of macrofauna by reducing the spawning biomass of fishery below

desired level (Taylar et al., 2003). It is the biggest threat to marine environment, even

greater than that of other human caused disruptions. Over-fishing influence changes in

species composition and biodiversity can occur with progressive reduction of large,

long lived and high value of predators’ species. Moreover, over-fishing may also

reduce genetic diversity of intertidal organisms as well as marine fisheries resources in.

generally.

Oil spills and crude oil is another most important factor affecting costal resources

(mangroves and their associated fauna). Oil spills is the release of liquid petroleum

hydrocarbon into the environment, especially marine areas, due to the human activity

and is a form of pollutants (Pezeshki et al., 2000). Oil spillage can be a resulting of

corrosion of oil pipes, storage tanks, sabotage and sometimes carelessness during oil

production or unloading operation. The impacts of spillage on coastal areas are

enormous whereby lives have been lost and the habitat and ecology have also been

damage due to the presence of hydrocarbons that disrupts the existing community

(Fukuyama and Vanblaricom, 1997).

Oil spills may have adverse effect on in fauna due to smothering or toxic (Kingstone et

al., 1995). The Florida oil spills in Buzzards Bay, resulting immediate mortality of

12

intertidal and sub tidal benthic fauna documented by Sander, (1978). The result show

that, the opportunistic polychaete, initially settled into disturbed areas at densities up

200,000 individual per meter square but after about seven months, densities of this

species dropped as other species replaced it (Sander, 1978). Oiled areas showed large

fluctuations in abundance and species composition while un-oiled areas were relatively

stable over time (Sander, 1978). The decrease in both density and species richness are

signs of disturbance to the macrofauna community brought about the oil spills. Hall,

(1994) define disturbance as a discrete event in time that disrupts an ecosystem,

community or population structure and changes resources, substrate availability or

physical environment.

Although direct effect mortalities from oil pollution may comprise much of the loss of

many macrofauna, however animals that are able to survive the spills may be subjected

to other threats such as predation. The study done by Elmgren et al., (2006) after the

Florida barge spills 700,000 liters of oil into the salt marsh sediments, the result show

that crabs exposed to the oil avoided burrowing, suffered delaying response, lower

feeding rate, thus oil residues are therefore biologically active and affect crabs

population. The effect of oil pollution on marine coastal area is a serious problem for

both mangrove and their associated macrofauna. So, this study will provide basic

information about the effect of oil spills to marine coastal area and to give out

recommendation which will be used by police and decision makers in conservation

program.

13

2.5 Conceptual Framework

Conceptually, mangrove and their associated macrofauna have been impacted through

natural factors like, salinity, temperature, pH dissolved oxygen. However,

anthropogenic activities such as cutting mangrove, salt production and oil spills

pollution have impacted this ecosystem in alarming rate. These factors cause serious

environmental degradation through habitat destruction and fragmentation that result to

improper habitat as well as inadequate food resources for variety of intertidal

organisms including macrofauna. Moreover, under severe condition local extinction

may occur. However, some measures such as planting of new mangrove seedlings and

unloading operation should be taken. Furthermore, knowledge of environmental

conservation for the local community including the effect of over-harvesting of coastal

resources as well as the use of illegal fishing gears should be given so as to ensure that

our biological resources we have are healthier and more sustainable.

14

Figure 1: Conceptual Framework on anthropogenic impacts on mangrove and their

associated macrofauna

-Mangrove

deforestation

-Low

distribution of

macrofauna

Local extinction

Mangroves & associated

macrofauna

Anthropogenic

factors

-Cutting

mangroves

-Oil spills

-Over fishing

-Salt

production

Environmental

factors

-Climate change

-Temperature

-Dissolved

oxygen

-pH

-Salinity

Conservation

measures

-Alternative

project

-Planting

seedlings

-Knowledge

for community

-Proper use of

Coastal

resources

-High distribution

of mangroves

-High distribution

of macrofauna

15

CHAPTER THREE

METHODOLOGY

3.1 Study area

The study was conducted in Pemba Island which is the second major Island of

Zanzibar archipelago. It lies between 40˚52' and 60˚31' South of equator. It is about 50

km from the coast of Tanzania in the Indian Ocean. It covers an area of 980 square

kilometers. The archipelago is surrounded by the coral reefs, beautiful sandy beaches,

natural and unexploited lagoons, mangrove swamps which are rich in marine life

(Kombo et al., 2006). This study was focused on two mangrove forests. Wesha and

Ngezi Natural forest reserve. Wesha is located in Chake Chake district in the Western

part of Pemba Island. It is 15 km from Karume Airport. The area is non protected and

is highly impacted through anthropogenic activities such as cutting mangrove for

building purposes, charcoal and lime production and overfishing. Apart from that the

area also have been impacted by oil spills pollution from unloading operation and

crude oil generated by the power plant that are located closely to Wesha coastal area.

Ngezi natural forest reserve is located on the Northern part of Pemba Island (39˚42´E

and 40˚55´S) in Micheweni district. It is about 50 km off the coast of Mainland

Tanzania. The gazetted area is recorded as 1456 ha (Kombo et al., 2006). It is a natural

forest reserve which is protected under the Government authority and people were

prohibited to utilize coastal resources legally. The areas were selected for the following

reasons: Wesha has been selected because it is an open access which is highly

impacted through anthropogenic activities including oil spills pollution. On other hand,

Ngezi mangrove forest was selected as a control site, due to the fact that it is a

16

protected area with no or less anthropogenic activities including sources of oil

spills/contamination.

Figure 2: Map of Pemba Island showing the study areas (Modified by Bentje, 1990)

3.2 Population and Climate

The population density of Wesha was 3,209 and that of Ngezi was 185,326 (URT,

2002). Their annual growth rate is 5% which is greater than the National average of

3.1% (RGOZ, 2009).The climate is dominated by bimodal rain fall pattern, the main

rain season (Masika) occurs between March and June. The short rains (Vuli), usually

17

starts in October and ends in December. Some inter-monsoonal precipitation takes

place (Jumah et al., 2010). However, there is some variation in mean annual rainfall

among the study areas. The mean annual rain fall of Wesha is 1760 mm and the

average temperature ranges between 26 °C and 32 °C. Meanwhile, the mean annual

rain fall of Ngezi natural forest reserve is 1,860 mm, the long rains average 363mm per

month and the short rains average 175 mm per month (Beentje, 1990; Abdullah et al.,

1996).

3.3 Research design

The study was tailored through both quantitative and qualitative approaches.

Quantitative approach was used so as to increase level of reliability of gathering data

(Cassel & Symon, 1994). Qualitative approach was employed because it enabled the

researcher to obtain more and in-depth information. This is because the researcher can

interact with the research subjects by their own language and their own term. The

combined methods/approach ensured high degree of reliability of data, understanding

of the contextual aspects of the research, flexibility and openness of data collection and

more holistic interpretation of the research problem. Quantitative design was used to

collect information about the distribution and abundance of macrofauna, mangrove

diversity and regeneration rate as well as physico-chemical parameters of pore water.

Since qualitative design was used to collect data about anthropogenic activities that

could affect the distribution and abundance of mangrove macrofauna.

3.4 Sample Design and Sample Size.

Random sampling techniques were employed in biodiversity assessment and physico-

chemical properties of pore water through establishment of sampling plots and

18

quadrants. This technique was selected based on the nature of the forests and it was

more convenient and quick method of obtaining samples. Nine plots of 10 m x10 m

and 90 quadrants of one meter square (1 m x 1 m) were established along each study

area. However, stratified sampling was employed in selecting members for assessment

of anthropogenic activities. Furthermore 50 respondents were selected from each study

area (Ngezi and Wesha) to form a total of 100 respondents. Stratified sampling was

selected because it is the sampling technique that can minimize sampling error and also

reduce population variability (Folz, 1996).

3.5 Data collection method

3.5.1 Primary Data.

3.5.1.1 Preliminary Survey.

A preliminary survey was conducted in each study site so as to characterize the study

area for proper methodology design and identify working stations for establishment

and selection of sample plots.

3.5.1.2 Fauna and mangrove characterization

The transect survey was conducted to determine the distribution and abundance of

macrofauna, mangrove diversity and regeneration rate as well as determination of

physicochemical parameters of pore water along the study areas. A total of 3 plots of

10 m x 10 m each were randomly established in each zone (upper, middle and lower

zones), so as to make a total of nine plots in each study area. In each plot, 10 quadrants

of one by one meter square (1 m x 1 m) were established. A plot of 10 m x 10 m were

used to identify mangrove species while quadrant of one meter square was used to

count mangrove seedlings and collection of macrofauna located at the sediment and

19

those attached to the mangrove trunks (30 cm and 60 cm height from the sediment).

The collected macrofauna were identified using field guide book (Richmond, 1998).

3.5.1.3 Physicochemical parameters

Also quadrant of one meter square was used to collect pore water for determination of

physicochemical parameters such as pH, temperature and salinity using pH meter,

thermometer and salinometer, respectively. The instruments were introduced in a

prepared hole of about 30 cm deep and then the measurement was recorded (Plate 1).

All samples were collected during low tide.

Plate 1: Determination of physico-chemical parameters of pore water in Ngezi forest

3.5.1.4 Assessment of anthropogenic activities

Survey to investigate anthropogenic activities that can affect the mangrove and their

associated macrofauna were conducted using questionnaires. The questionnaires were

given to the local villagers who were depending directly on mangrove resources for

supporting their livelihood needs. The information required from the villagers

20

including source of income and how they were benefited from the coastal resources. In

addition to that, checklists were supplied to the Government officers from the

department of forest from each study area to collect information about the

anthropogenic activities conducted by the local community. Also other information

about measures to be taken so as to reduce these anthropogenic impacts to the coastal

areas was collected. Furthermore, focus group discussions with the local leaders were

conducted to collect necessary information about the impact of different activities

performed by local community and its consequence to the mangrove forest and to their

associated fauna.

3.5.2 Materials used

A measuring tape was used to measure the size of sampling plot and the distance

between one plot to another. Quadrants were used to assess the distribution and

abundance of macrofauna, mangrove seedlings, and collection of pore water for

determination of physicochemical parameters. Salinometer was used to measure pore

water salinity, thermometer for pore water temperature, pH meter for pore water pH,

and questionnaires were used to collect information from the respondents. Moreover,

field forms were used for ecological data assessment as well as physicochemical

parameters of pore water.

3.6 Data analysis

Data were analyzed using Statistical package (InStat 3 Trial version and Statistical

Package for Social Science (SPSS) version 16). Anthropogenic data were analyzed

using SPSS, in which cross tabulation were used to get percentage of respondents

perception about factors affecting the distribution of macrofauna. However ecological

data and physicochemical parameters of pore water were analyzed using statistical test

21

such as t-Test, Pearson correlation, chi-square and ANOVA. Also Microsoft Excel

2003 was used to draw charts and graphs that were used to describe ecological data as

well as physicochemical parameters of water. Species diversity of mangrove and

macrofauna were determined using Shannon-Wieners which is more effective in

determination of species diversity.

H' = -Σ (Pi x ln Pi)

Where, i= 1

H' = Shannon diversity index

Pi= Fraction of entire population. Made up species i

S = number of species accounted.

Σ= Sum from all species.

3.7 Data validity and reliability

Validity increases the accuracy and usefulness of findings through eliminating much

confounding variables which allow greater confidence in the findings of the study.

Since both qualitative and quantitative approaches were used so as to increase the

validity and reliability of data. Quantitative approach was used in biodiversity

assessment from the field to ensure the validity and reliability of data because data is

obtained directly from field using transects through identification and counting.

However, qualitative approach also was used to increase the validity of data because

the data were collected directly from the respondents through questionnaires which are

more effective for assessing social issues. Moreover, pre-testing of data collection

methods (field survey and questionnaires) were conducted so as to increase validity of

data.

22

CHAPTER FOUR

RESULTS AND DISCUSSION

4. 1 Objective one: To examine mangrove distribution and regeneration rate

along the study area.

This objective covers the following sub titles, mangrove zonation, mangrove diversity,

mangrove species density, mangrove regeneration, and factors affecting mangrove

regeneration rate.

4.1.1 Mangrove zonation

Three different zones of mangrove distribution have been observed in Ngezi as well as

in Wesha mangrove forest (Table 1). The results indicated that, Avicenia marina,

Ceriops tagal and Xylocarpus granatum may thrive in all three zones of mangrove

forest while Lumnitzera racemosa and Hertiera littoralis were observed only in upper

zone of mangrove forest. The situation could be attributed by the interaction of

environmental and physical factors of that particular ecosystem. The findings

corresponds to the previous study on distribution of mangrove, that have been done by

Odum and Malvor, (1990) who reported that C. tagal, A. marina and X. granatum

species can dominate the shoe line from upper sub tidal to lower intertidal zones. In

addition to that, the occurring of Avicenna marina in all three zones of mangrove forest

is due to their ability of salt tolerance (Semesi, 2001). Furthermore the study indicated

that Bruguiera gymnorrhiza, Rhizophora mucronata and Sonneratia alba were

observed in middle as well as in lower zones. This observation have been supported by

previous studies like (Smith, 1987; Mendelssohn & McKee, 2000; Soud, 2004) who

reported that double distribution may occur when species are more abundant in two

different zones of that particular ecosystem.

23

Table 1: Distribution of mangrove species in three zone of Ngezi and Wesha forest

Mangrove

zone

Ngezi Wesha

Upper zone X. granatum, L .racemosa, H. littoralis, C.

tagal. A. marina and B. gymnorrhiza.

X. granatum, L. racemosa,

C. tagal, A. marina, H.

littoralis

Middle zone X. granatum, B. gymnorrhiza, C. tagal,

R. mucronata , S. alba and A. marina

R. mucronata, B. gymnorrhiza,

C. tagal, S. alba and A. marina

Lower zone S. alba, C. tagal, R. mucronata. X.

granatum and B. gymnorrhiza

R. mucronata, C. tagal, S.

alba, B. gymnorrhiza & A.

marina

Source: Field data 2012

In Ngezi, X. granatum, B. gymnorrhiza and R. mucronata were the dominant species at

upper, middle and lower zones, respectively. Unlike Ngezi, in Wesha, A. marina, were

the dominant species in upper zone while R. mucronata were observe as the dominant

species in middle as well as lower zones. Generally description of mangrove zonation

depicts a pattern that extends from shore to inland regions (usually higher in elevation).

Tidal flooding, land elevation, and salinity are often attributed as controlling factors in

mangrove zonation. The existence of distinct zones, each dominated by different

species is often evident in well developed mangal mangrove zonation, however the

distribution pattern is not uniformly throughout the world, it depend upon complex

physical and biological interaction occurring in that particular ecosystem (Odum and

Malvor,1990).

24

4.1.2 Mangrove diversity

The study indicated that 8 mangrove species were identified in Ngezi as well as Wesha

mangrove forests (Table 2). The results varied to the previous study like that of

Othman (2005) who identifies 5 mangrove species in Pete and six 6 mangrove species

in Maruhubi mangrove forest in Zanzibar. It has been observed that X. granutum were

the dominant species in Ngezi that constituted 23.3% of the total mangrove trees

identified. On other hand A. marina were observed as the dominant species in Wesha

and they constituted about 22.1% of the total mangrove trees identified in Wesha

mangrove zones (Table 2).

Table 2: Mangrove species & and their percentage in Ngezi and Wesha.

Source: Field data (2012)

The study indicated that, Ngezi has large number mangrove trees compared to Wesha

(Table 2). However, the areas which were involved in data collection are of the same

size. The large numbers of mangrove trees in Ngezi could be attributed by nature of

forest (conserved area) which is protected under the Government authority in which

S/no Species Ngezi- no. of

Trees/ha

(%) Wesha-.no. of

Trees/ha

%

1 X. granatum 55 23.3 9 4.63

2 L. racemosa 13 5.50 8 4.1

3 H. littoralis 10 4.23 4 2.06

4 A. marina 11 4.66 43 22.16

5 B. gymnorrhiza 47 19.9 30 15.46

6 C. tagal 49 20.76 35 18.0

7 R. mucronata 34 14.40 41 21.11

8 S. alba 14 7.2 24 12.30

Total 236 100 194 100

25

local communities were controlled by in utilization of these valuable resources. Apart

from that, also local community were restricted to perform most activities that could

affect the existing biological resources which are important to surrounding community

as well as to increase national income through ecotourism. In general, the study

indicated that, the species diversity index (H') was 1.85 and 1.87 for Ngezi and Wesha,

respectively. The study showed that, there were no differences in species diversity

between these two mangrove forests. The situation may be attributed by presence of

almost homogeneous physico-chemical parameters that determine the distribution of

mangrove trees Worldwide. Also, the corresponding physical conditions (e g soil type)

between the two forests may contribute in reducing diversification of mangrove

species along the study sites. It has been observed that, large area of Wesha mangrove

forest has been covered by sandy soil and silt like that of Ngezi thus why the species

that can tolerant in Ngezi can also exist in Wesha mangrove ecosystem.

In term of zonation, the results showed that, species diversity index (H') of Ngezi was

1.60, 1.77 and 1.5 for upper middle and lower zones, respectively. Meanwhile the

species diversity index (H') for upper, middle and lower zones Wesha was 1.4, 1.89

and 1.56, respectively. Furthermore, the statistical test indicated that, there was no

significant difference in mangrove species diversity between the three zones of the

forests (two tailed test P = 0.2038, t = 0.277, Df = 2).

However the study indicated that, middle zones Ngezi exibit high species diversity

followed by the upper and finally lower zone. Meanwhile in Wesha the situation is

different, whereby high species diversity were observed in middle zone followed by

lower and finally to upper zones. In general the results showed that, high

26

diversification of mangrove species have been observed in middle zones. Probably

edaphic and environmental factors contribute to high species diversity in middle zones.

However, at the upper and lower zones of both forests shows slightly diversification of

mangrove species (Figure 3).

1

1.5

2

2.5

Upper Middle Lower

Div

ers

ity

in

dex

( H

')

Station

Ngez

Wesha

Figure 3: The mangrove species diversity in three zones of Ngezi and Wesha.

4.1.3 Mangrove species density

The study indicated that the average species density of mangrove trees was 19,400 and

23,400/ha for Wesha and Ngezi, respectively. The results showed that the individual

mangrove species having high density in Wesha were A. marina, R. mucronata, and C.

tagal, that constituted 43 (22.16%), 41 (21.11%) and 35 (18%), respectively. However,

X. granatum, C. tagal and B. gymnorrhiza were observed as the species having high

density in Ngezi mangrove forest and they constituted 55 (23.3%), 49 (20.7%) and

47(19.9%), respectively (Figure 4). Moreover, the statistical test showed that, there

was no significant difference in number of mangrove species density between Ngezi

and Wesha mangrove forests (two tailed test P > 0.5315, t = 0.6581, Df = 7).

27

2

12

22

32

42

52

62

Man

gro

ve s

pecie

s

Den

sity

/h

a

Mangrove species

Ngezi

Wesha

Figure 4: Mangrove species density in Ngezi and Wesha mangrove forest.

Furthermore, the results indicated that, X. granatum in Ngezi are the one having high

density compared to other species within the forest. The situation could be attributed

by its unique character to exist in all three zones of the forest. Also the situation have

been contributed by it morphological structure whereby most people were not

interested in harvesting this species for building purposes, boat making and tannin

extraction which are major threats for mangrove trees. However in small extent, they

were used as a wood fuel and lime production. Another important factor that made this

species to be more abundantly is due to the presence of dry dehiscent fruits that contain

four seeded chambers and each, contain a single seed, so that their seeds can stay for

very long period within the pericarp but still they are viable. Moreover conservation

status of the forest may also contribute to maintain that situation. A part from that, C.

tagal also has been observed as the second most species having high species density in

Ngezi. Probably high regeneration rate may influence high species density of

mangrove (Soud, 2004).

28

Unlike Ngezi, in Wesha Avicenia marina has been observed to exhibit high species

density. This is because, the species are not common harvested by most people for

economic purposes and thus why they have high species density. However in our

discussion with the Government officers from the department of Natural resources

Pemba, one of Government officer reported that traditionally, some people use A.

marina species for medicinal purpose especial for washing young baby.

In zonation wise, the results showed that in Ngezi the average mangrove trees counted

was 22, 32 and 25 for upper middle and lower zone, respectively. Similarly in Wesha

the average mangrove trees counted was 20, 21, and 23 for upper, middle and lower,

respectively (Figure 5). However results indicated that middle zone of Ngezi consist of

greater number of mangrove trees followed by lower and finally upper zone. Unlike

Ngezi, In Wesha lower zone has higher number of mangrove trees followed by middle

and finally upper zone (Figure 5). In general middle and lower zone of the both forest

consist of large number of mangrove trees. The situation could be explained by the

presence of large number of mangrove species like B. gymnorrhiza, C. tagal and R.

mucronata that were considered having high regeneration rate (Soud, 2004).

Furthermore statistical test (ANOVA) indicated that, there was no significant

difference in number of mangrove trees between three zones of Ngezi and Wesha

mangrove forest (P > 0.2375).

29

10

15

20

25

30

35

40

upper middle lower

Man

gro

ve

tree

s (D

ensi

ty/m

²)

Station

Ngezi

Wesha

Figure 5: Number of mangroves trees per zone in Ngezi and Wesha.

In general, the results indicated that all three zones of Wesha exhibit less number of

mangrove trees compared to Ngezi (Fig. 5). High population pressure in utilization of

mangrove trees for construction materials, fuel wood consumption, lime and charcoal

making that are performed by most local communities for supporting their livelihood

needs influence low mangrove density in Wesha. Apart from that, the study indicated

that 20% of the total respondents of Wesha said that, oil spills resulted from the

unloading operation and crude oil generated by the power plant contribute to lower

mangrove density. Through field survey large number of dead mangroves have been

observed along Wesha coastal area where the power plant is located and unloading

operation takes place (Plate 2) It has been observed that, the area near the power plant

has been completely degraded and some conservation measures have been taken

through establishment of small project as a pilot so as to restore the degraded area by

planting native species of mangrove seedlings in some part of Wesha coastal area

(Plate 2).

30

Plate 2: Dead mangroves and planting of seedlings near the power plant at Wesha.

4.1.4 Mangrove regeneration rate

Mangrove regeneration refers to the process whereby seedlings become mature/adult

plants that can contribute in conserving the important gene pool of that particular

species. Mangrove seedlings refer to individuals shorter than one meter. A total of

28,400 and 16,800 individual seedlings/ha were counted in Ngezi and Wesha,

respectively. The study further indicated that, the regeneration rate was 3.1 and 1.8

seedlings/m² for Ngezi and Wesha respectively. The statistical test showed that there

was a significantly higher in regeneration rate of mangrove seedlings between Ngezi

and Wesha mangrove forests (One tailed test P > 0.0191, t = 2.549, Df = 7).

According to the results, Wesha mangrove ecosystem has low regeneration rate

compared to Ngezi. The situation could be explained by the physical disturbance

through utilization of mangrove trees along Wesha that affect mangrove species

density which are source of new seedlings. Apart from that, environment degradation

31

caused by crude oil generated by the power plant that is located along Wesha coasta

area also contributes low regeneration. Unlike Wesha, Ngezi have been observed to

exhibit high regeneration rate. The situation could be attributed by the conservation

status of the forest whereby most activities that could affect the existing biological

diversity were not allowed legally.

In term of zonation, in Ngezi the mangrove seedlings counted was 77 (27.11%), 111

(39.08%) and 96 (33.80%) for upper middle and lower zone, respectively. Similarly in

Wesha the mangrove seedlings counted was 42 (25%), 62 (36.90%) and 64 (38.09%)

for upper middle and lower zones, respectively. The results indicated that in Ngezi

higher regeneration rate were observed in middle zone followed by lower and lastly

upper zone Unlike Ngezi, in Wesha higher regeneration rate have been observed in

lower zone followed by middle and finally upper zones (Figure 6). In general the

results indicated that middle and lower zones exhibit higher regeneration rate

compared to upper zone. The situation could be explained by the presence of large

number of mangrove species having high regeneration rate like R. mucronata, C. tagal

and B. gymnorrhiza.

32

30

50

70

90

110

130

upper middle lower

No

.of

Seed

lin

gs

(Den

sity

/m²)

Station

Ngezi

Wesha

Figure 6: Regeneration rate per zone in Ngeazi and Wesha mangrove forest.

The findings agree with the previous studies such as that of Jumaha et al., (2001) and

Soud, (2004) who reported that mangrove species like, C. tagal, R. mucronata and B.

gymnorrhiza have higher regeneration rate. Moreover, the statistical test indicated that

there was a significantly higher in regeneration rate in three zones of both forests (P >

0.0179, t = 7.381, Df = 2).

At species level, the results showed that, in both study sites C. tagal, R. mucronata and

B. gymnorrhiza exhibit high regeneration rate. In Ngezi the regeneration rate for the

three mangrove species which are probably having high regeneration rate were C.

tagal, R. mucronata and B. gymnorrhiza that constituted 22.18%, 23.2%, and 27.8%,

respectively. Like Ngezi, in Wesha C. tagal, R. mucronata and B. gymnorrhiza

constituted 19.0%, 30.35% and 23.21% of the total seedlings, respectively (Table 3).

These findings corresponds to the previous study on mangrove regeneration done by

Jumah et al., (2001) who reported that C. tagal, B. gymnorrhiza and R. mucronata are

mangrove species having high rate of regeneration.

33

Table 3: Regeneration rate per species in Ngezi and Wesha mangrove forest.

Source: Field data (2012)

4.1.5 Factors affecting mangrove regeneration

Generally, regeneration are influenced by number of factors such as salinity, types of

seedling, predators (such as crabs, barnacles and gastropods), shade, tidal inundation,

high temperature, oil spills pollution and other anthropogenic activities performed by

the local community living around the coast. These factors may affect natural habitat

as well as environmental conditions that are important in supporting proper growth and

development of mangrove seedlings (Fukuyama and Vanblaricom, 1997). For

example, physico-chemical parameters of water are among the most important factors

affecting mangrove regeneration in any mangrove ecosystem. The study revealed that,

the physicochemical parameters of water were almost the same in both sites. However,

the results showed that Wesha exhibit very low regeneration rate compared to Ngezi.

Human factors such as clear felling of mangrove for construction materials, wood fuel

Ngezi Wesha

S/no Mangrove

species

No. of

seedlings

Percentage

(%)

No. of.

seedlings

Percentage

(%)

1 X .granatum 40 14.08 15 8.92

2 L. racemosa 10 3.52 3 1.78

3 H. littoralis 5 1.76 2 1.19

4 A. marina 18 6.33 23 13.69

5 B. gymnorrhiza 79 27.81 39 23.21

6 C. tagal 63 22.18 32 19.04

7 R .mucronata 66 23.23 51 30.35

8 S. alba 3 1.05 3 1.78

Total 284 100 168 100

34

consumption and salt production are the common activities that lead to mangrove

deforestation. As many mangrove species reproduce through viviparous mode of

reproduction whereby seedlings grow while still they are attached to the parent plant.

So, physical disturbance of mangroves may influence low production of mangrove

seedlings.

Apart from high rate of mangrove utilization by the local communities around Wesha

coastal area, also field observation showed that large numbers of mangrove trees

closely to the power plant are completely dead and propagules have been observed.

Possibly, crude oil generated by the power plant influence mangrove deforestation

which is directly associated to lower the production of new seedlings. The observation

is consistent with the previous studies on mangrove deforestation. Example, (Snedaker

et al., 1981 and Getter et al., 1981) who reported that chronic effect of oil pollution

contamination influence defoliation and death of mangrove seedlings. Moreover, the

major consequence of die back of mangroves is to influence erosion along the coast

due to the completely degraded area that is unable to resist with water current mostly

during high tide. Environmental degradation along the coast may influence mangrove

seedlings to be carried by water current (Shunula, 2001).

Through focus group discussion which was conducted with government officers and

local leaders, Officer in charge of Wesha port reported that for very long period,

unloading operation was not well managed. He stated that, during unloading operation,

a significant amount of oil have been observed around Wesha coastal area whereby

storage tank of petroleum are located (Plate 3).

35

Plate 3: Showing Wesha port where storage tanks of petroleum are located

In this area large numbers of dead mangrove have been observed. The situation was

the major factor that influence low mangrove density which directly affects the

availability of seedlings. The observations correlate with the previous observation done

by Fukuyama and Vanblaricom (1997) who reported that, oil pollution may disrupt the

existing community by affecting physiological activities of the living tissues, soak the

sediment as well as shortage of oxygen (anoxic condition) whereby oxygen is very

important in growth and development of seedlings.

4.2 Objective two: To examine the distribution and abundance of macrofauna

This objective covers the distribution, species richness, species diversity and

abundance of macrofauna in general, abundance of crustaceans, gastropods and

bivalves. Also tables and figures will be used to elaborate the findings.

36

4.2.1 Distribution of Macrofauna

Mollusks and arthropods were the only two phyla of macrofauna encountered during

the study period. The 2 phyla consist of 3 classes namely gastropods, bivalves and

crustacean with 19 families, 29 genera and 33 species. Out of 33, 25 species of

macrofauna comprises of 4 species of gastropod, 2 species of bivalve and 19 species of

crustaceans were identified in Ngezi. Likewise in Wesha, 23 species of macrofauna

that comprises of 6 species of gastropods, 13 species of crustaceans and 4 species of

class bivalve were identified. In addition, further analysis of the results revealed that

out of 33 species, 10 species were only identified in Ngezi while 8 species were only

identified in Wesha, with 15 species found in both sites (Table 4). These findings

correspond with the previous study that was conducted by Othman, (2005) who

identifies thirty (30) species of macrofauna from Maruhubi and Pete mangrove forest

in Zanzibar. However the observation varied from the study done by Schrijvers et al.,

(1995) who reported 16 species of macrofauna in mangroves of Gazi Bay in Kenya.

Also Hart, (1994) reported forty three species of macrofauna from mangroves swamp

of Port Harcourt area of the Niger Delta.

37

Table 4: Distribution of macrofauna in the study sites (+ found, - not found)

Source: Field data 2012

Furthermore, it was observed that, C. decollata and T. palustris (gastropods) were the

dominant species in Ngezi meanwhile I. ephippium (bivalves) was the most dominant

species in Wesha. The occurring of large number of gastropods in Ngezi, could be

S/N Class Individual species Sites

Wesha Ngezi

1

Crustaceans

Eurycarcinus natalensis - +

2 Scylla serrata + +

3 Sarmatium grassum + +

4 Matuta.lunaris + -

5 Macrophthalamus grandidieri + -

6 Macrophthalamus depressus + -

7 Cardisoma carnifex + + 8 Uca inversa Inversa + + 9 Uca uvillei + + 10 Charybdis natator + + 11 Caenobita violascens + -

12 Metopograpsus thukuhar + + 13 Uca tetragon + + 14 Uca lactea annulipes + + 15 Epixanthus frontalis - + 16 Calapa hepatica - + 17 Thalamita poisson - + 18 Neosarmatium smith - + 19 Sesarmops impressus - + 20 Female uca - + 21 Clibanarius danai - + 22 Philyra platchira - + 23 Ocypode ryderi - + Total 13 19

Gastropods

Terebralia palustris + +

24 Fusnus colus + +

25 Planaxis sulcatus + +

26 Cerithidea decollata + +

27 Rhinoclavis senesis + -

28 Phasianella nivosa + -

Total 6 4

29

Bivalves

Isognomon ephippium + +

30 Anadara antiquata + -

31 Trachycardium pectiniforme + -

32 Saccostrea cuculata + +

Total 4 2

Total species 23 25

38

explained by the conservation status of the forest whereby local community were

restricted in utilization of coastal resources legally. Apart from the conservation status,

that species were not more preferred by local community for food. On other hand, the

occurring of bivalves (I. ephippium) as a dominant species in Wesha could be

attributed by unique characters possessed by that particular species to exist in stressed

environment. Probably are among the bivalve species having special immunity mainly

supported by hemocytes which are important in eliminating the parthogen by

phagocytosis as supported by study done by Coles and Pipe (1994). That is why they

are more resistant to stressed environment.

The study further indicated that gastropods like Rhinoclavis senesis and Phasianella

nivosa and some bivalve species like Anadara antiquata and Trachycardium

pectiniforme were among the 8 species of macrofauna that were only identified in

Wesha. Probably these species are less susceptible to environmental degradation and

that is why they were found only in Wesha mangrove zones which are highly impacted

through human activities including pollution from the power plant. On other hand, the

study indicated that Eurycarcinus nataensis, Epixanthus frontalis, and Philyra

platchira were among the ten species of macrofauna that were only identified in Ngezi

but not identified in Wesha. It is likely that, these species are more susceptible to

anthropogenic factors including oil spill pollution which are the major source

environment degradation in Wesha. The observation relate to the observation of

Suchanek (1993) who reported that, animals in soft stratum area are more susceptible

from pollution. Moreover, the results showed that, the species that were only identified

in Ngezi constituted about 30.30%, while those that were only identified in Wesha they

constituted 24% of the total species identified. However, the study revealed that, there

39

was an overlapping of species whereby 15 species of macrofauna were identified in

Ngezi as well as Wesha mangrove zones. The percentage of species overlapping was

45.45% which is greater compared to the species that were only identified in either

sites. The situation could be explained by, that species are well adapted to the

environment.

In zonation wise, the results indicated that, 14, 21, and 24 species of macrofauna were

identified in upper, middle, and lower zones of Ngezi mangrove forest, respectively.

Like Ngezi in Wesha upper, middle and lower zones constituted 11, 19 and 23 species

of macro fauna, respectively. In generally the study indicated that upper zones exhibit

less species of macrofauna compared to middle and lower zone of both systems. The

situation could be explained by the presence of long period of low tide as well as long

period of exposure to air with the additional of high temperature variation.

Furthermore, the study indicated that, no bivalve species were identified in upper zone

of either site. This is because bivalves are filter feeders, so they need an environment

of long period of high tide, less temperature variation as well as less period of exposure

to the air.

The study further indicated that some species of gastropod (C. decollata) and bivalves

(I. ephippium and S. cuculata) were observed on mangrove trunks as their main

habitat. Gastropods like C. decolata were found in wide range of habitats, from the

sediment, 30cm and 60cm height from the sediment. Similarly the results indicated that

some bivalve species like I. ephippium and S. cuculata were also observed on

mangrove trunks at the different height from the sediment.

40

Moreover, the results indicated that Ngezi has high species richness (where n= 25)

compared to Wesha (where n = 23). The situation could be explained by the nature of

the forest as conserved area in which local communities were restricted to utilize these

resources legally. Apart from that, large coverage area of Ngezi forest also contributes

high species richness through providing adequate space and food supply. On other

hand low species richness in Wesha are influenced by human disturbance such as clear

felling of mangrove for building purposes, salt production and over-fishing. In addition

to that, oil spills pollution and crude oil generated by the power plant that are closely to

Wesha coastal area also may influence low population density of macrofauna.

Furthermore, the study revealed that species diversity index (H') for Ngezi was 1.77

while that of Wesha was 2.00. This indicated that, Wesha has high species diversity

compared to Ngezi. It is likely that, the presence of some species of gastropods and

bivalves which are more resistant to worse condition contribute high species diversity

of macrofauna in Wesha mangrove ecosystem.

In term of zonation the study indicated that, in Ngezi the species diversity index (H')

was 1.68, 1.81, and 1.75 for upper, middle and lower zones, respectively. Similarly in

Wesha the species diversity index (H') was 1.61, 2.4 and 1.8 for upper, middle and

lower zones, respectively (Figure 7). In generally high species diversity were observed

in middle followed by lower and finally upper zones. The situation could be explained

by the presence of adequate amount of food resource, less temperature that reduce

animal desiccation as well as less period of exposure to the air (Ajao and Fagade,

2002). However, the study revealed that upper zone Wesha has least species diversity

index compared to other zones of both forests. Human disturbance like, clear cutting of

mangroves and waste generated by the power plant which results high degradation of

41

this zone influence low species richness as well as diversity. Furthermore the study

indicated that, no grater change in species diversity index in Ngezi mangrove zones

(Figure 7). The situation could be attributed by less or no anthropogenic impacts in

Ngezi mangrove forest.

1

1.5

2

2.5

3

Upper Middle Lower

Mac

rofa

una

div

ersi

ty

Ind

ex (

H' )

Station

Ngezi

Wesha

Figure 7: Diversity index (H') of macrofauna in three zones of Ngezi and Wesha

4.2.2 Abundance of macrofauna

A total of 4,126 individual macrofauna were counted during the study period in which

2,586 and 1,540 were counted in Ngezi and Wesha mangrove forest, respectively. In

Ngezi 2,586 individual macrofauna which is equivalent to 62.6% of the total

macrofauna identified. Out of which 936, 1260 and 390 were bivalves, gastropods and

crustacean (crabs), respectively. Similarly in Wesha 1,540 macrofauna which is

equivalent to 37.32% of the total macrofauna comprises 682, 595 and 263 of bivalves,

gastropods and crustaceans (crabs), respectively (Table 5). The study revealed that, the

individual macrofauna per meter square was 29 and 17 for Ngezi and Wesha,

respectively.

42

Table 5: Abundance of macrofauna species identified in Ngezi and Wesha.

Source: Field data 2012

S/no Class Individual species Number.of

macrofauna

Wesha Ngezi

1

Crustaceans

Eurycarcinus natalensis 0 4

2 Scylla serrata 11 18

3 Sarmatium grassum 29 31

4 Matuta.lunaris 11 0

5 Macrophthalamus grandidieri 16 0

6 Macrophthalamus depressus 14 0

7 Cardisoma carnifex 13 17

8 Uca inversa Inversa 39 48

9 Uca uvillei 26 42

10 Charybdis natator 12 16

11 Caenobita violascens 3 0

12 Metopograpsus thukuhar 21 19

13 Uca tetragon 23 27

14 Uca lactea annulipes 45 55

15 Epixanthus frontalis 0 4

16 Calapa hepatica 0 3

17 Thalamita poisson 0 8

18 Neosarmatium smith 0 18

19 Sesarmops impressus 0 47

20 Female uca 0 6

21 Clibanarius danai 0 19

22 Philyra platchira 0 3

23 Ocypode ryderi 0 5

Total 263 390

Gastropods

Terebralia palustris 78 107

24 Fusnus colus 5 2

25 Planaxis sulcatus 10 9

26 Cerithidea decollata 471 1142

27 Rhinoclavis senesis 3 0

28 Phasianella nivosa 28 0

Total 595 1260

29

Bivalves

Isognomon ephippium 445 666

30 Anadara antiquata 3 0

31 Trachycardium pectiniforme 4 0

32 Saccostrea cuculata 230 270

Total 682 936

Total macrofauna 1540 2586

43

Moreover, the statistical analysis indicated that, there was no significant difference in

number of macrofauna between the sampling sites (P > 0.1442, t =1.497, Df = 32).

Similarly other test indicated that there was no significant difference in number of

macrofauna in three zones of Ngezi mangrove forest (ANOVA P = 0.91). The same

test indicated that there was no significant difference in number of macrofauna in

Wesha mangrove forest (P = 0.86). It has been observed that Ngezi mangrove forest

was dominated by gastropods that constituted about 48.7% followed by bivalves that

constituted about 36.19% of the total individuals counted. Unlike Ngezi, Wesha

mangrove forest was dominant by bivalve species that constituted 44.28%, followed by

gastropods that constituted 38.6% of the total individuals counted. Crabs were found to

be the least abundant in both study sites and they constituted about 15.08% and

17.07% for Ngezi and Wesha, respectively. Moreover the study showed that, only

epifauna were considered, however fish and prawn were excluded due to the time

factor, because all the ecological data were collected during the low tide.

In general, the results indicated that Ngezi mangrove forest has large number of

macrofauna compared to Wesha, even though the recorded physico-chemical

parameters of Ngezi and Wesha which are the most important factors that determine

the distribution of macrofuna were almost the same. It is likely that, there are other

factors that influence low distribution of macrofauna along Wesha mangrove forest.

The situation could be attributed by physical disturbance such as cutting mangrove,

overfishing that initiate habitat destruction as well as fragmentation. Apart from that,

also oil pollution and crude oil generated by the power plant that causes serious

ecological risks as well as environmental disturbance to Wesha mangrove ecosystem

influence low distribution of macrofauna. The observations correspond to the previous

44

studies on distribution of macrobenthos like, Pearson and Rosenberg, (2003); Surugiu,

(2005); Hatje et al., (2008) who reported that, the distribution of macrobenthos can be

affected by both anthropogenic factors as well as toxic compounds from the petroleum

hydrocarbons including heavy metals.

4.2.2.1 Crustacean (Crabs)

A total of 653 crabs were counted during the study period, out of which 390 (59.7%)

were found in Ngezi while 263 (40.27%) were found in Wesha. In general, the study

revealed that a total of 5 and 3 crabs /m² were counted in Ngezi and Wesha mangrove

forests, respectively. The statistical test (two tailed test) indicated that there was a

significantly higher in number of crabs in Ngezi than Wesha (P < 0.0472, T = 2.102,

Df = 22). The presence of huge number of crabs in Ngezi is influenced by nature of the

forest which is a protected under the Government authority whereby local people were

restricted to perform most activities that may affect or lowering biological diversity

present in that ecosystem.

In term of zonation, the results indicated that, in Ngezi, upper, middle and lower zones

comprises 38.2% (149), 34.1% (133), and 27.69% (108) of the total crabs identified

respectively. Similarly in Wesha, the upper, middle and lower zones comprises 39.16%

(103), 33% (87) and 27.7% (73) of the total crabs identified respectively (Fig 8).

45

50

70

90

110

130

150

170

upper middle lower

No

. o

f C

rab

s

(Den

sity

/m²)

Station

Ngezi

Wesha

Figure 8: Number of crabs per zone in Ngezi and Wesha mangrove forest

Statistically, t-Test showed that there was a significant higher in number of crabs

between the three zone of the study sites (P < 0.0042, t = 10.89, Df = 2) for Ngezi and

(P < 0.0048, t = 10.115, Df = 2) for Wesha.

In general the study indicated that upper and middle zones supports large number of

crabs compared to lower zone. These findings agreed with previous studies for

instance Ajao and Fagade, (2002) who conclude that, the distribution of crabs were

relatively higher in upper zone compared to middle and lower zones in mangrove

swamp of Port Harcourt area of the Niger Delta. Possible physical changes in the

substrate composition in availability of maximum organic carbon may attribute for

greater abundance of crabs in upper zone. In addition to that, the presence of rich

nutrients in the Avicenia marina leaves which are mostly found in upper zone attribute

high population density of crabs in upper zone rather than in the middle and lower

zones. Also, most crab species are well adapted to areal breathing and thus are able to

withstand longer exposure periods and adoption which allow them to colonize the

more landward of intertidal areas. Moreover, it is likely that, the presence of large

46

number of crabs in upper zone is due to the presence of lower number of predators that

depend directly on such kind of organisms as a source of food.

At the species level, the results showed that, Uca annulupes, Uca inversa inversa and

Sesarmorp impresus that constituted 14.18%, 12.28% and 12.19% of the total crabs

counted, respectively were the dominant crab species in Ngezi. However, in Wesha,

Uca annulupe, Uca inversa inversa and Sarmatium Grassum were observed as the

dominant crab species and they constituted 17.13%, 14.96% and 11.2% of the total

crabs counted, respectively. The study indicated that Uca annulupes were the dominant

crab species in Ngezi as well as in Wesha mangrove zones. The results corresponds

with the study of Hartnnoll et al., (2002) who reported that, Uca annulupes is the most

abundant among the crab species in East African Mangroves brachyurans.

4.2.2.2 Gastropods

In Wesha, a total of 595 individual gastropods which was equivalent to 32.07% of the

total gastropods were identified and counted. They belonged to Terebralia palustris,

Planaxis sulucatus, Rhinoclavis.senesis. Phasionella nivosa, Fusnus colus and

Cerithedea decollata. Similarly, in Ngezi 1,260 individual gastropod which was

equivalent to 67.92% of the total gastropods were counted. They belonged to

Terebralia palustris, Planaxis.sulucatus, Fusnus colus and Cerithedea decollata. The

study showed that 14 and 7 individual gastropods /m² were counted in Ngezi and

Wesha mangrove zones, respectively. Furthermore, the statistical test indicated that,

there was a significant higher in number of gastropods between Ngezi and Wesha (χ²

=14.95, P < 0.0001, Df = 5.

47

The presence of fewer number of gastropods in Wesha than Ngezi could be attributed

by less species richness that are influenced by increasing anthropogenic activities such

as cutting pressure of mangrove trees which are the main habitat of most gastropod

species especially tree dwellers. Apart from lacking appropriate habitat oil spills

pollution that may introducing toxic materials from aromatic hydrocarbons.also

influence less number of gastropods in Wesha. On other hand, lager number of

gastropods in Ngezi could be attributed by the conservation status of the forest that

promotes high species richness.

In zonation wise, in Ngezi, the upper, middle and lower zone comprised of 26.81%

(338), 36.11% (455) and 37.06% (467) of the total gastropods counted, respectively.

Similarly, in Wesha the upper, middle and lower zones comprised of 28.4% (169),

37.14% (221), and 34.45% (205) of the total gastropods counted, respectively. The

study revealed that more gastropods were observed in middle and lower zones rather in

upper zone (Figure 9). It is likely that, the presence of hard shells that protect them to

be taken by their predators influence them to inhabit at middle and lower shore of the

intertidal areas where large number of predators are found. Apart from that, low

salinity that were and recorded at the middle and lower zones favor high population

density of gastropods. Furthermore, other statistical test indicated that, there was no

significant difference in number of gastropods between the three zones of the forest

(One way ANOVA P > 0.964 for Ngezi and P > 0.323 for Wesha).

48

100

200

300

400

500

600

upper middle lower

No

. o

f G

ast

rop

od

s

(Den

sity

/m²)

Station

Ngezi

Wesha

Figure 9: Number of gastropods per zone in Ngezi and Wesha mangrove forest.

At the species level, the results revealed that, C. decollata and T. Palustris were the

dominant species of gastropods in both sites and they constituted 90.6%, and 8.49% for

Ngezi and 79.15% and 13.1% for Wesha. Even though less gastropods were counted in

Wesha, but more species were identified. The situation could be explained by the

presence of wood boring gastropods that survived worst condition even in a spilled

area. The results correspond with the study of Powell, (1990) who reported that some

species of gastropods are resistant on harsh environment.

Moreover, the study revealed that some species of gastropod (C. decollata) have been

observed in mangrove trunk as their main habitat. The study revealed that a total of

1142 and 471 C. decollata were counted in Ngezi and Wesha, respectively during the

study period. In Ngezi 34.5% of the total C decollata were observed in 30 cm while

62.69% were observed in 60 cm height from the sediment and only 2.71% were

observed in sediment. Like Ngezi in Wesha mangrove forest 37.15%, 55.4% and

7.43% of the total C. decollata were observed in 30 cm, 60 cm and sediment

49

respectively. The observation are consistent to the observation of the previous study on

distribution of macrofauna along the intertidal area conducted by Ajao and Fagade

(2002), who reported that gastropods and bivalves are relatively tolerant to physical

and chemical variations in the environment and they are found in a broad range of

habitat.

4.2.2.3 Bivalves

A total of 682 individual bivalves which is equivalent to 42.15% of the total bivalves

were counted in Wesha and they belonged to Isognomon ephippium, saccostrea

cuculata, Anadara antiquata and Trachycardium pectiniforme. Meanwhile 936

individual bivalves which is equivalent to 57.84% were counted in Ngezi and they

belonged to Isognomon ephippium and Saccostrea cuculata. The study further

indicated that, 10 and 8 bivalves /m² were counted in Ngezi and Wesha, respectively.

Furthermore, the statistical test showed that, there was a significant higher in number

of bivalves between Ngezi and Wesha mangrove ecosystem (χ² = 14.65, P < 0.021, Df

= 3). The results indicated that, more bivalves were counted in Ngezi that belonged to

only 2 species. Unlike Ngezi, in Wesha less bivalves were identified that belonged to 4

species. The presence of more number of bivalves in Ngezi could be influenced by

protective nature of the forest which influences more species richness. On other hand

less number of bivalves in Wesha could be attributed by high population pressure that

affects the richness of biodiversity. On other hand more species of bivalves identified

from Wesha mangrove ecosystem could be explained by the presence of some

bivalve’s species that probably having special immunity mainly supported by

hemocytes which are important in eliminating pathogen by phagocytosis (Coles and

50

Pipe, 1994). These results corresponds to the study done by Powell, (1990) who

reported that, some species of gastropod and bivalve are more resistant in hush

condition even in a contaminated area. It has been reported that, some bivalve species

their hemocytes produce lysosome enzymes and antimicrobial molecules which

contribute to the destruction of pathogen.

For the case of zonation, the results indicated that, in Ngezi, upper, middle and lower

zones constituted 0 (0%), 447 (47.75%) and 489 (52.24%) of the total bivalves counted

respectively. Similarly in Wesha, upper, middle and lower zones constituted 0 (0%),

315 (46.18%) and 367 (53.81%) of the total bivalves counted respectively. In general,

the results indicated that, middle and lower zone of Wesha have been observed to

support very few numbers of bivalves compared to Ngezi (Figure 10). Habitat

destruction through cutting mangrove and undersized fishing influence low population

density of macrofauna in Wesha. However, the statistical analysis indicated that there

was no significant difference in number of bivalves between the three zones of the both

sites (One way ANOVA P < 0.0266) for Ngezi and (P > 0.1664) for Wesha.

51

150

250

350

450

550

650

upper middle lower

No

.of

biv

alv

es

(Den

sity

/m²

)

Station

Ngezi

Wesha

Figure 10: Showing number of bivalves per zone in Ngezi and Wesha.

Moreover, the study showed that no bivalve species were observed in upper zone of

either site, but mainly were observed in middle and lower zones (Figure 10). The

situation could be explained by a specifically applicable to such animals as they are

filter feeders, they feed on filtering micro-organisms from the water and thus rely on

high tides for their existence. Apart from that, the occurring of large number of

bivalves in middle and lower zones may be due to the environmental condition having

low salinity than the area having high salinity. The results correspond to the previous

studies on distribution of macrofauna in intertidal area like that of Frith et al., (1996);

Boehs et al., (2004) who reported that bivalve species are widely distributed in

seaward area of the shore.

At the species level, the results showed that I. ephippium and S. cuculata were the

dominant bivalve species in both Ngezi and Wesha mangrove forests. I. ephippium and

S. cuculata they constituted 71.1% and 28.84% of the total bivalves counted in Ngezi,

respectively. Similarly in Wesha, I. ephippium and S. cuculata were observed as the

52

dominant bivalve species that constituted 65.24% and 33.2% of the total bivalves

identified, respectively.

In addition to that, the study indicated that some bivalve species were observed on

mangrove trunks as their main habitat (Plate 4). A total of 1,111 I. ephippium were

counted during the study period. In Ngezi 666 I. ephippium counted, out of 35.1% and

64.8% were observed in 30 cm and 60 cm height on mangrove trunks from the

sediment, respectively. Meanwhile in Wesha 445 I. ephippium counted, 24.7% and

75.5% were observed in 30 cm and 60 cm height from the sediment, respectively.

Plate 4: Showing (bivalve) Isognomon ephippium attached to the mangrove trunks

The study further indicated that, a total of 500 S. cuculata were counted in Wesha and

Ngezi mangrove forest. In Wesha 230 S. cuculat counted, 31.7% and 68.2% were

observed in 30 cm and 60 cm height from the sediment, respectively. Similarly in

Ngezi 270 S. cuculata counted, 36.2% and 63.7% of the total S. cuculata were

53

observed in 30 cm and 60 cm height from the sediment, respectively. (Table 6) The

study further indicated that large number of tree dwelling animals ware observed on 60

cm height from the sediment rather than in 30 cm from the sediment. This is due to

their morphological structure that enabled them to thrive in different habitat, even in

dead wood of mangroves. However, the results showed that no animals were observed

above 60 cm height from the sediment.

Table 6: Percentage of tree dwelling animals in different heights in Ngezi and Wesha.

Source: Field data 2012

In zonation wise, the study showed lower zones of both sites possessed large number

of tree dwelling animals compared to middle and upper zones. This is because,

majority of tree dwelling animals (bivalves) are filter feeders, so they preferred on

habitat which are characterized by long period of submerged in water and very short

period of exposure to air. The results also supported by other previous studies like that

of Frith et al., (1996) who reported that, tree dwelling animals mainly occurred in

seaward area rather than on landward of mangrove zones. Moreover, the results

indicated that neither I. ephippium nor S. cuculata have been observed in sediment.

S/no Species Ngezi Wesha

30 cm 60 cm Sediment 30 cm 60 cm Sediment

1 C. decollata 34.5% 62.69% 2.7% 37.15% 55.5% 7.43%

2 I. ephipium 35.1% 64.8% - 24.4% 75.2% -

3 S. cuculata 36.2% 63.7% - 31.7% 68.2% -

54

4.3 Objective three: To assess the association between environmental conditions

(salinity, temperature and pH) to the distribution of macrofauna.

This objective covers three physicochemical parameters of pore water which are

salinity, pH and temperature. Figures and tables have been used to elaborate the

results.

4.3.1 Salinity

The results indicated that, the salinity value ranged from 32 ‰ – 40.5‰ for Wesha and

25.8‰ - 39.7‰ for Ngezi mangrove forest. Furthermore, the statistical analysis

showed that there was no significance difference in salinity value between Ngezi and

Wesha mangrove forest (One tail P < 0.1798, t = 1.034, Df = 4). The results

correspond to the previous studies. For examples Richardson (2010) reported that

salinity in coastal areas ranges on 32‰ - 35‰. However the result differs from other

studies like that of Vijayalakshmi et al., (1993) who reported that the salinity value

ranges from 34‰.-48‰ in mangroves of Gulf of Kachchh. The study further indicated

that, highest salinity value was recorded at Wesha while the lowest was recorded at

Ngezi which was 40.54‰ and 25.88‰ respectively. Salinity plays a crucial role on

distribution and abundance of mangrove macrofauna at large extent. It has been

identified as a key environmental variable affecting the distribution of organisms and

influencing critical physiological process (Jansson, 1994). It is important because it

represents ecological master factor for marine organisms.

In zonation wise, the results showed that in Wesha the salinity value was 40.5‰,

35.8‰, and 32.8‰ for upper middle and lower zones, respectively. Similarly in Ngezi

the salinity value for upper, middle and lower zones was 39.75‰, 25.88‰ and

55

28.75‰, respectively (Figure 11). The study indicated that in Wesha the salinity value

decreases from upper zone to middle zone and lower zone. The upper zone Wesha

exhibit high salinity value compared to middle and lower zones. The situation could be

explained by high temperature and subsequent evaporation of sea water that coupled

with increased salinity (Zingda et al., 1987). However in Ngezi the situation is quite

different, high salinity value was recorded at upper zone followed by lower and lastly

middle zone of the forest. According to the results middle zone of Ngezi exhibit very

low salinity compared to the other zones of both sites. This is due to the fresh water

influx from the river Kunguni that discharged their water through this zone, thus why

the salinity value in this zone was found to be very low compared other zones (Figure

11).

20

25

30

35

40

45

upper middle lower

Sal

init

y v

aria

tio

n

( ‰

)

Station

Ngezi

Wesha

Figure 11: Variation of salinity in Ngezi and Wesha mangrove forest.

The salinity is the most important a biotic factor that determines the distribution and

abundance of macrofauna along the coast. In general the results showed that, low

salinity support large number of macrofauna mostly gastropods and bivalves. Bivalves

are filter feeders so most of the time they need water for their survival and that is why

56

they preferred in lower shore of mangrove zone in which low salinity was recorded and

adequate amount of water/ moisture is available (Boehs et al., 2004). However, the

study revealed that more crab species were observed on upper and middle shore of the

mangrove and very few were observed in lower zone. This is because most crab

species preferred to the habitat having high saline rather than low saline.

The results is supported by other studies like that was conducted by Anger et al.,

(2005) who reported that low salinity (hyposaline) can result mortality of crabs due to

imbalance in osmoregulatory mechanism. In addition to that, hyposaline have negative

effect on crab species by increases energy expenditure and reduce food consumption

and absorption. In general low salinity influence high population density of

macrofauna, thus why huge numbers of macrofauna were identified in middle and

lower zones rather than in upper zone (Table 7). In relation to the distribution of

macrofauna the statistical analysis indicated that, there was a strong correlation on

distribution of macrofauna and salinity variation in both mangrove forest (r = 0.9578,

r² = 0.9173, p < 0.0001).

Table 7: Percentage of macrofauna per zone in Ngezi and Wesha mangrove forest.

Source: Field data 2012

Zone/Study site Ngezi Wesha

No. of

macrofauna

Percentage (%) No.

of.macrofauna

Percentage

(%)

Upper zone 487 18.83 272 17.6

Middle zone 1035 40. 623 40.4

Lower zone 1064 41.1 645 42

Total 2586 100 % 1540 100 %

57

4.3.2 Pore water pH

The pH of water is the second most important a biotic factor that may influence many

biological and chemical processes in natural waters (Saad, 1998). The results showed

that the recorded pH ranged from 6.55 to 6.6 and 6.42 to 6.52 for Ngezi and Wesha

respectively. The study revealed that the highest pH value was recorded in Ngezi

which was 6.6 while the lowest pH was recorded in Wesha which was 6.42.

The study further indicated that, there was no significant difference in pH value

between Ngezi and Wesha mangrove ecosystem (two tailed test P > 0.1729, t = 2.081,

Df = 2). The results are also supported by the previous study on physicochemical

parameters, Example, Rogothaman and Patil (1995) who reported that the pH of pore

water ranged from 6.7 to 7.4 in the mangroves along Vellar estuary. However, the

results varied from the study of Govindasany and Kannan (1991) who reported that the

pH of pore water ranged from 4.9 to 7.2 in the mangroves of Pitchavaram.

In term of zonation, the results showed that, in Ngezi the pH value was 6.56, 6.6 and

6.5 for upper middle and lower zones respectively. Similarly in Wesha the salinity

value was 6.52, 6.49 and 6.42 for upper middle and lower zones respectively. The

study further indicated that upper zone Wesha exhibit high pH value followed by

middle and lastly lower zones. However, in Ngezi the situation is different, high pH

value was recorded at the middle zone followed by upper and finally lower zone

(Figure 12). The situation could be explained by the fresh water influx from the river

Kunguni that discharged their water directly to the middle zone Ngezi. Furthermore,

the study indicated that, there was no great variation of pH value along the study sites

(Figure 12).

58

6

6.2

6.4

6.6

6.8

7

upper middle lower

pH

vari

ati

on

Station

Ngezi

Wesha

Figure 12: Variation of pH per zone in Ngezi and Wesha mangrove forest.

In relation to the distribution of macrofauna, the results indicated that low pH favor

high population density of macrofauna like gastropod and bivalve species that is why

huge number of gastropods and bivalves were observed and recorded at the lower

shore where low pH value were recorded. These results are also supported by previous

study on effect of physicochemical parameters on distribution of macrofauna along

intertidal area done by Boehs et al., (2004) who reported that bivalves are widely

distributed in environment with low pH. Furthermore, the statistical analysis (Pearson

correlation) indicated that there was a strong correlation between pore water pH and

the distribution of macrofauna in both study sites (r = 0.9591, r² = 0.9785, p < 0.0001).

4.3.3 Pore water temperature

Like salinity and pH, temperature plays an important role on distribution and

abundance of macrofauna in a particular area of niche. In the present study, the results

indicated that the pore water temperature recorded ranged from 28.44˚C - 29.81˚C and

29.1˚C - 31.57˚C for Ngezi and Wesha, respectively. The highest recorded temperature

59

was 31.57˚C in Wesha while the lowest temperature was 28.44˚C in Ngezi. Moreover,

the statistical analysis indicated that there was no significant difference in temperature

variation between Ngezi and Wesha mangrove forest (two tailed test P < 0.0900, t =

3.105, df = 2).

These results is also observed earlier by several workers like Ragothaman and Patil

(1995) who reported that the pore water temperature ranged from 27˚C and 33˚C in

Tapi estuary; Watts et al., (1982) reported that pore water temperature in Gulf of

Karachchh ranging between 25˚C to 30˚C, Selvam et al., (1992) reported that pore

water temperature along Kakinada mangrove ranging between 26.9˚C to 31.2˚C.

However, the results varied to the study of Kesavan et al., (2007) who reported that

pore water temperature in Godavari mangrove ranging from 19˚C to 37˚C. The highest

temperature recorded at Wesha mangrove forest could be explain by free open space

whereby local community were observed to involved in utilization of mangrove trees

for construction materials, wood fuels, sea weed farming and lime and charcoal

making which are major threats of mangrove community.

Moreover, the die back of mangrove forest may attribute in temperature fluctuation in

Wesha. Generally, surface water temperature is influenced by the intensity of solar

radiation, evaporation and fresh water influx. Unsuitable temperature may affect

growth rates, length of life, reproductive capacity as well as intra and interspecific

competition. In fact such effect may have some impact, directly or indirectly on

distribution of mangrove macrofauna. Moreover the major obvious effect of unsuitable

temperature is the resulting of exclusion of certain species of that particular habitat

(Choudhury et al., 1984).

60

In term of zonation the study indicated that in Ngezi the recorded temperature was

29.81˚C, 28.6˚C and 28.44˚C for upper middle and lower zone, respectively. Similarly

in Wesha the recorded temperature was 31.57˚C, 29.4˚C and 29.1˚C for upper, middle

and lower zones, respectively. According to the results upper shore of both systems

exhibit high temperature followed by middle and lower shore (Figure 13). In relation to

distribution and abundance of macrofauna, more numbers of macrofauna were

observed in middle and lower zones rather than in upper zone. The situation could be

explained by the presence of low temperature that reduces water loss or desiccation

which is a major threat for intertidal animals. Extremely high or low temperature may

have negative effect on macrofauna such as mortality, low rate of hatching, desiccation

and under sevier condition animals can migrate from one habitat to another. Therefore

moderate temperature plays an important role for the proper growth and development

of macro fauna (Steele and Steele, 1991). The study further indicated that there was a

strong negative correlation between temperature variation and distribution number of

macro fauna (Pearson correlation - r = 0.9588, r² = 0.9784, p < 0.0001).

28

29

30

31

32

upper middle lower

Tem

pera

ture

vari

ati

on

( ˚C

)

Station

Ngezi

Wesha

Figure 13: Variation of temperature per zone in Ngezi and Wesha mangrove forest.

61

Furthermore, the present study showed that, no great variation of physicochemical

parameters between the study areas, however differences in distribution and abundance

of macrofauna have been observed at large extent between the two sites. Possibly there

are other factors that contribute lower distribution of macrofauna at Wesha rather than

environment factors. Cutting mangrove, over-fishing, and contamination from the oil

spill pollution with the addition of crude oil generated by the power plant which is

closely located to Wesha coastal area influence low distribution and abundance of

macrofuna in Wesha.

4.4 Objective four: To investigate anthropogenic activities affecting the

distribution and abundance of macrofauna

This objective covers respondent profile, clear felling of mangroves, over-fishing, oil

spills pollution and salt production as an anthropogenic factors affecting the

distribution and abundance of macrofauna.

4.4.1 Respondents profile

Fifty respondents from each study site were involved in this study to make a total of

one hundred (100) respondents. Among these 56% were males and 44% were females

(Table 8). Out of these 89% were married while 11% were unmarried (Table 8). In

considering educational status 21% of the total respondents were illiterate, 30%

attained primary education, 46% attained secondary education and the remaining 3%

have completed Advance level and above (Table 8). The study further indicated that

28% of the total respondents were involved in fishing activity, 24% in farming activity,

32%) in collection of marine resources and the remaining 16% were involved in other

economic activities (Table 8).

62

Table 8: Respondent profile

Category Number of respondents Percentage (%)

Gender

Male 56 56

Female 44 44

Marital Status

Married 89 89

Single 11 11

Type of Activities

Fishing 28 28

Farming 24 24

Collector of marine resources 32 32

Others 16 16

Education

Never attended 21 21

Primary Education 30 30

Secondary education 46 46

A level and Above 3 3

Source: Field data 2012

4.4.2 Anthropogenic activities

During the study period, four anthropogenic factors were investigated as major threats

on distribution and abundance of macrofauna along the study sites.

63

Table 9: Percentage of anthropogenic factors in Wesha and Ngezi

Source: Field data 2012

4.4.2.1 Clear cutting of mangroves

The results indicated that, 38% of the total respondents in Wesha agreed that clear

felling of mangrove for several purposes contribute to lower the distribution and

abundance of macrofauna while in Ngezi only 30% of total respondents agreed that

low distribution and abundance of macrofauna is the resulting of clear felling of

mangrove trees (Table 9). The study showed that, in Wesha large number of the local

communities were involved in clear felling mangrove for supporting their livelihood

needs. The situation could be explained by free open space whereby local communities

were involved in utilization of coastal resources without any restriction from

Government. The results correlate well with the previous studies like that of Semesi,

(1992, 1998) who reported that most destructive activities on mangrove are the

clearing for several purposes like construction materials, lime production and boat

making.

In contrast to Wesha, in Ngezi the results indicated that only 30% of the total

respondents agreed that felling of mangrove trees influence low distribution of

macrofauna. The situation could be explained by the conservation status of the forest in

which local communities were restricted in utilization of mangrove resources legally.

Apart from that, Ngezi has large area covered by terrestrial forest which is an

Site Cutting mangrove Oil pollution Over-fishing Salt production

Ngezi 30% 0% 28% 42%

Wesha 38% 20% 32% 10%

64

alternative resource for charcoal making, building materials, and other purposes like

fuel wood consumption. In considering the importance of mangrove trees to the

macrofauna, further study on the Mesoamerican reef has revealed that reefs close to

mangrove areas has twenty five (25) times more fish of some species rather than in

area where the mangroves have been cleared.

The felling of mangroves lead to loss of habitat, shore line, organic matter production

and species dependent on the habitat and mangrove based food chain (Semesi, 1991).

In general mangrove forest may be felled for several purposes like aquaculture ponds,

salt pans, agricultural use like rice fields, roads construction, industrial development,

boat making and village development. The commercial needs are the most important

activities that lead on over exploitation of mangroves (Semesi, 1991).

Clear felling of mangroves is considered as major threat of this unique system. In our

discussion with Government officers and local leaders, the head of forest department

Pemba reported that, the majority of local people along Wesha coastal area were

involved in cutting mangroves as a major source of income (Plate 5). The situation are

influenced by lacking of employment from the Government and they have no

alternative income generating project for improving their livelihood needs and thus

why they were involved in utilization of these coastal resources much with out

considering their roles to other living creatures living in that particular ecosystem.

However, the study revealed several negative impacts of clear felling of mangrove

trees to their associated macrofauna in number of ways. Felling of mangroves

contribute in habitat destruction that result refuges related problems, loss of breeding

ground for fish as well as other macrofauna in particular.

65

Plate 5: Local peoples in utilization of mangrove trees for boat making along Wesha

Moreover the ecological data from the field observation showed that Wesha have low

species richness, low distribution and low abundance of macrofauna compared to

Ngezi. The situation could be explained by habitat destruction from the clear felling of

mangrove trees which are the main habitat as well as source of food for variety of

species of macrofauna like crabs and gastropods. Loss of natural habitat is among the

major threats facing intertidal animals that directly affect their population density. The

results corresponds with the other studies like that of Kaly et al., (1997) who reported

that severely damaged mangrove site in North Queensland lead to a significant loss of

both Nitrogen and phosphorous from the soil which are indirectly related to decline in

macrofauna especial crabs. The study further indicated that clear felling of mangroves

influence low composition, distribution and abundance of macrofauna through

increasing stress with increasing temperature as well as exposure to air (Robertson and

Duke, 1990).

66

Apart from raising temperature and increasing exposure to air, felling of mangrove

trees, affect energy transfer because they are valuable food resources of macrofauna

like crabs and gastropods. It is likely that low distribution and abundance of

macrofauna in Wesha mangrove ecosystem are influenced by inadequate food

resources through clear felling of mangrove. Mangroves are important in providing

goods and services to many organisms living along the estuary environment. The

results correlate to the previous findings on mangrove deforestation done by Stuart et

al., (1990). In addition the productive nature of mangrove communities which are often

important link between many biological diversity and other near shore community

(Alongi, 1989; Robertson, 1991; Lee, 1995; Kathiresan and Bigham, 2001).

Like any other ecosystem, mangrove link number of macro as well as micro-organisms

to make it as complete system. Each unit plays any important role in supporting the life

of others, so, the removal of a single unit will affect the flow of energy of that

particular ecosystem. Therefore, the clear felling of mangrove trees in Wesha

contributes low distribution and abundance of macrofauna through disruption of either

components of concerned system. Furthermore, loss of mangrove leaves that are

important in contributes substantially to formation of detritus which support many

coastal fisheries, contributes low distribution and abundance of macrofauna.

4.4.2.2 Over-fishing and illegal fishing gears

The results showed that 28% of the total respondents in Ngezi agreed that low

distribution and abundance of macrofauna are influenced by over fishing activities that

are performed by local community living along the coast illegal. However the study

indicated that, 32% of the total respondents in Wesha agreed that low distribution of

67

macrofauna are influenced by over-fishing (Table 9). This observation corresponds to

the previous studies like that of Myers and Worm, (2003) who reported that over-

fishing as a major factor that influence biodiversity loss. In Ngezi, low percentage of

respondents that agreed, low distribution of macrofauna are influenced by overfishing

could be explain by the nature of the forest which is protected and local people were

just utilize these valuable resources under supervision otherwise they utilize the

resources illegally. Unlike, Ngezi, in Wesha large percentage of the respondents agreed

that, low distribution of macrofauna are influenced by overfishing. The situation could

be explained by free space Wesha in which majority of local communities living near

and around Wesha coastal area were involved in utilization of these resources with out

consider the size and age of macrofauna that are landed.

Over-fishing is among the anthropogenic activities affecting the distribution and

abundance of macrofauna. It occurs when fish and other living resources are caught at

a rate which exceeds the maximum harvest that allows the population to be maintained

by reproduction (Myers and Worm, 2003). Over fishing and the use of illegal fishing

gears are among factors influencing of low population density of macrofauna in

intertidal area as well as threatening the endangered species due to harvesting even non

target animals (Jones, 1992; Gray, 1997; Janning and Kaiser, 1998; Myers and Worm,

(2003). The situation results biodiversity loss due to the incidental capture of non

target animals. Apart from that, long term over-fishing reduces the abundance,

spawning potential and possibly population parameters like growth and maturity of

macrofauna (Myers and Worm, 2003).

68

Moreover, over-fishing reduces age and size structure, sex ratio, species composition

of the target resources as well as of their associated and dependent species. Over-

fishing and the use of illegal fishing gears lead to clear changes in community

composition of benthic infauna and epifauna which may have far-reaching implications

for the integrity of marine food webs (Darrel et al., 2012). In addition to that over

fishing and the use of illegal fishing gears may alter habitats most notably by

destroying and disturbing bottom topography and associated habitat e.g. sea grass and

benthic communities as well as direct mortality of benthic infauna.(Kaiser & Spencer,

1996, Schwinghamer et al., 1998).

4.4.2.3 Oil spills

The study indicated that in Ngezi no respondents agreed that low distribution and

abundance of macrofauna are influenced by oil spills pollution. However, the study

revealed that 20% of the total respondents in Wesha agreed that low distributions of

macrofauna are influenced by oil spills pollution (Table 9). The situation could be

explained by the presence of port that are mainly used for unloading operation of

petroleum as well as the presence of power plant that are located closely to Wesha

coastal area (Plate 6). The power plant discharged their wastes directly along the coast

where varieties of living organisms are located. Oil spills from the unloading operation

and crude oil generated by the power plant are the main source of environmental

degradation that influence low population density of macrofauna in Wesha.

69

Plate 6: Crude oil generated by power plant along Wesha costal area.

Pollution from the oil spills continue to damage mangrove as well as to their associated

fauna (Semesi, 1998). Oil contamination can damage animals in the mangal, both in

sediments and submerged mangrove roots (Elmgren et al., 2006). Through field

observation, the study indicated that low distribution and abundance of macrofauna

were identified in Wesha compared to Ngezi The results corresponds to the previous

studies like Levy et al., (1980) who reported that, the population density of macrofauna

have been reduced by 60% after the Galeta spills in Panama. The decreasing of

population density is a part of related to loss of root surface on which most macrofauna

like bivalves and some gastropods are located as their main habitat. Therefore, loss of

mangrove vegetation influence low distribution of macrofauna due to lack of suitable

habitat, lack of adequate food from the mangrove leaves as well as refuges related

problems (Plate 7).

70

Plate 7: Showing dead mangroves near the power plant at Wesha coastal area.

It has been reported that, oil spills pollution and industrial wastes induced adverse

effect on macrofauna due to smothering or toxic (Kingstone et al., 1995). Oil spills

pollution can induced direct mortality of macrofauna that results low population

density as well as low species richness due to ecological disturbance (Hall, 1994).

Apart from direct mortality of macrofauna, oil spills and waste from the power plant

may also associated to long term effect such as predation, avoided burrowing activities,

delaying response, lower feeding rate due to oil residue which are biological active that

can affect population density of macrofauna (Elmgren et al., 2006). Moreover, unlike

Wesha in Ngezi, the situation is different whereby the population density of

macrofauna was high. This could be explained by the absence of source of oil pollution

that causes seriously ecological damage that could affect the population density of

macrofauna along the intertidal area like Wesha which is highly polluted.

71

4.4.2.4 Salt Production

The results indicated that 10% of the total respondents in Wesha agreed that low

distribution and abundance of macrofauna was influenced by solar salt production

activities. However, the results showed that in Ngezi 42% of the total respondents

agreed that low distribution and abundance of macrofauna was influenced by salt

production activity that are conducted by local community along the intertidal area

(Figure 14)

0

10

20

30

40

50

Perc

en

tage o

f R

esp

on

den

ts (

%)

Anthropogenic factors

Ngezi

Wesha

Figure 14: Common anthropogenic factors in Ngezi and Wesha mangrove forests

Solar salt productions are man-made systems for the extraction of salt from seawater,

by means of solar and wind evaporation. They are also coastal aquatic ecosystems of

great ecological importance, as they are characterized by considerable habitat

heterogeneity. They combine a spectrum of aquatic environmental types along salinity

gradient. Solar salt works are closely related to natural transitional water ecosystems,

as they are located at the land-sea interface and their lower salinity part presents many

72

similarities with coastal lagoons, regarding both the abiotic environment and the biota

(Evagelopoulos & Koutsoubas, 2007).

Salt solar production is among the anthropogenic activities that constitute greatest

threat on mangrove as well as to their associated fauna (Farnsworth, 1997; Semesi,

1998). It is associated with the clear cutting of mangrove forests, which are significant,

used as suitable habitat for animals living in the mangrove zones. Therefore, felling of

mangrove trees results habitat loss that influence low distribution of macrofauna along

the intertidal areas. Apart from that solar salt production elevate water salinity and

decreased water flow due to salt farms, the situation may kill number of macrofauna

that directly result low population density (Viles, 2005). Further study indicated that

population density of macro-invertebrates of coastal lagoon in Ghana was less in area

near the salt ponds compared to the area with out salt ponds (Molony and Parry, 2006).

Moreover, salt ponds increases water temperature whereby macrobenthose suffered

from elaveted temperature. The situation may affect the physiological process of

macrofauna and under sevier condition may result mortality of macrofauna that

directly influence low distribution and abundance of macrofauna.

However, the study indicated that the intensity of anthropogenic activities to the

distribution and abundance of macrofauna varies. The results indicated that in Ngezi

42% of the total respondents agreed that solar salt production influence low

distribution of macrofauna however, high population density have been observed. It is

likely that solar salt production has lees impact on distribution and abundance of

macrofauna compared to other activities that were identified during the study period.

Even though, Ngezi is a protected area but the results showed that in some extent local

73

communities were allowed to utilize some resources but in a proper way. For example

the study indicated that some local people were involved in solar salt production but it

might be the operation has less effect on distribution of macrofauna because the

activities are conducted at the open space which is far apart from the mangroves. Apart

from that, due to the nature of forest (conserved area) solar salt production in Ngezi act

as an alternative income generating project instead of depending on mangrove and

their associated macrofauna which are mainly prohibited.

Furthermore, the statistical analysis indicated that, there was a significant higher in

anthropogenic activities affecting the distribution and abundance of macrofauna

between Ngezi and Wesha (two tailed test P > 0.0399, t = 0.000, Df = 3). The same test

indicated that there was no significant difference in anthropogenic factors in Wesha

mangrove forest (P > 0.1342, t = 2.039, Df = 3). However, the study indicated that,

there was a significant differences in anthropogenic factors in Ngezi mangrove forest

with salt production being the most influencing factor (p > 0.0171, t = 4.811, Df = 3).

74

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

The results indicated that Wesha mangroves ecosystem have been greatly impacted

through human activities with the addition of oil spills pollution from unloading

operation and wastes generated by the power plant. The study indicated that, Wesha

(non protected) has low species density of mangrove trees with low regeneration rate

compared to Ngezi (protected) where the species diversity and regeneration rate were

observed to be higher. The results further indicated that, the physicochemical

parameters of pore water between the study sites were almost the same however

Wesha has low species richness, low distribution and low abundance of macrofauna.

Moreover, the study has shown that, cutting mangrove for different purpose, salt

production, over-fishing and oil spills pollution were the major anthropogenic

activities that affect mangrove as well as to their associated macrofauna along the

study sites. However the study indicated that, Wesha (non protected area) coastal zones

are more affected compared to Ngezi which is well protected. Even though Wesha

have been seriously impacted by number of anthropogenic factors, but it is more

diverse in macrofauna species due to the presence of bivalve species that are more

resistant to anthropogenic threats. Therefore intensive conservation practice is needed

so as to protect them.

75

5.2 Recommendations

Based on results of the present study the following recommendations should be taken:-

To reduce mangrove deforestation as well as low distribution and abundance of

macrofauna along Wesha mangrove forest, unloading operation and wastes from

power plant should be well manageable.

The degraded system along Wesha coastal area should be restored so as to bring back

as nearly as possible to its original state with high resistant and resilience.

Publicity and awareness campaign through film shows, organizing seminars, nature

camps, distributing publicity materials should be conducted not only to the local

community of Wesha coastal area but also for all people living along the coast so as

promote knowledge of environmental conservation which is important in supporting

many biological resources.

Alternative projects for income generation should be established for local community

living along the coast rather than depending only on harvesting of coastal resources for

supporting their livelihood to a large extent.

Establishment of community based conservation that involves local villagers in the

management of coastal resources will promote sense of ownership. The situation will

promote effective management of coastal resources which is very important for the

benefit of all stake holders and Government in general.

76

Under sized fishing of coastal resources mainly macrofauna such as crabs, bivalves

and gastropods should be burned.

Priority environmental protection must be incorporated into the planning of all major

projects as a fundamental requirement.

Comprehensive and more powerful environmental laws should be formulated and

enacted to enabling the relevant bodies to enforce such legislation.

Specific project of environmental conservation for Wesha mangrove forest should be

established due to the presence of variety of biological resources in order to make it

healthier like or more than other conservation area.

5.3 Limitation of the study

The following are some constraints that were encountered during this study. Firstly,

lack of instruments like (DO meter) for measuring dissolved oxygen which was the

most important parameter used to determine the distribution of macrofauna. Secondly

lack of financial support which is important for the successful completion of any study,

so due to financial constrain the study could not detect the level of oil pollution along

the study areas.

5.4 Area for further study

According to the results, the study revealed that, Wesha mangrove forest and their

associated macrofauna have been seriously impacted by combination of anthropogenic

factors including oil spills pollution. So these factors result serious ecological damage

77

in such away the degraded system are an able to provide goods and services needed by

biological diversity living in that particular ecosystem. Hence further scientific study is

needed to detect the level of oil pollution as well as the survival of planting seedlings

along Wesha coastal area. Apart from that, also further scientific study for the species

of macrofauna that are considered as less susceptible to the oil pollution is needed.

78

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98

APPENDEX I- QUESTIONNAIRE FOR LOCAL COMMUNITY

PART A. PERSONAL DETAIL

1. District…………………(2) Village ……………………(3) Shehia ……………

4. Sex………………………Male/ Female…………………………………………….

5. Marital status (1) Single (2) Married

6. Age…………………………………………………………………………………..

7. Name of the village …………………………………………………………………

8. Educational level (i) Not attend (ii) Primary (iii)Secondary (iv)Advance level and

above.

B. NATURAL RESOURCES UTILIZATION.

9. What is your occupation? …......................................................................................

(1) Fisherman (2) Coastal resources collector (3) Farmer (4) Others

10. For how long do you employ in this activity?

(a) 1-5 ( b) 6-10 (c ) 11-15) (d) 16 & above

11. Is this activity can satisfy your livelihood? (1) Yes (2) No

12. If yes, to what extent? (a) Some extent (b) Moderate (c) Large extent

13. What kind of natural resource which are mainly used for many local people in this

area?

(1) Mangrove forest (2) Terrestrial forest (3) Macrofauna (4) other

14. To what extent do the economic well beings in this village depend on mangroves

and their associated macrofauna? (a) Some extent (b) Moderate (c) Large extent

99

PART C. ANTHROPOGENIC FACTORS AFFECTING MANGROVE7THEIR

ASSOCIATED FAUNA

15. Do you know mangrove macrofauna? (1) Yes (2) No

16. If yes which macrofauna is more abundance?

(a) Gastropods (b) Mollusks (c) Crabs) (d) Other

17. Is there any changes on availability of mangrove macrofauna ?

(1) Yes (2) No

18. If yes, what kind of changes?

(a) Decreasing (b) Increasing (c) No change

19. For how long do you experience that changes?

(a) 1-5 (b) 5- 10 (c) 10- 15 (d) 15-20 (e) 21 and above

20. What are the common activities do you espect may affect mangroves and its

associated macro fauna. ?

a) Over fishing ( b) Cutting mangrove (c) Oil spill pollution (d) Salt production

21. Do you depend on mangrove macrofauna?

(1) Yes (2) No

22. If Yes for what purpose ? (a) Food ( b) Medicine (c) Source of income (d)

Others

23. What are the major economic activities undertaken by local people in this area?

a) Charcoal and lime production (b) Salt making (c) Cutting mangrove

24. Is there any relation ship between mangrove and macrofauna? (1)Yes (2) No

25. If yes, what will happen if people harvest much the mangrove forest?

a) Macrofauna decrease (b) Increase (c) Not affected

26. In what extent do local communities depend on mangroves?

(a) Some extent (b) moderate (c) large extent

27. Is there any source of oil pollution in this area? (1)Yes (2) No

100

28. If yes, list them ( a)………………(b)……………..(c)……………(d)…

29. Do you aspect that oil spills can affect mangrove and their associated fauna?

(1) Yes (2) No

101

APPENDEX 11-CHEK LIST FOR GOVERNMENT OFFICERS

1) What do you understand by mangrove macrofauna?

2) What is their main habitat?

3) Is there any economic importance of mangrove macrofauna?

4) Is there any relation ship between mangrove and macrofauna?

5) There is any change in availability of macrofauna within six years ago?

6) For your experience, what are common activities conducted by local people in this

area?

7) Which one of the above may affect mangrove ecosystem at all?

8) What factors that may influence local community to involved in utilization of

coastal resources in non sustainable manner.

9) How over-harvesting of coastal resources may affect the distribution of

macrofauna?

10) What do you aspect, if these activities are proceeds for next ten years?

11) Is there any NGO’S dealing with environmental conservation in area?

12) What measures to be taken so as to reduce these anthropogenic activities that could

affect the mangroves as well as to their associated macrofauna.?

Thank you for your contribution