ECOLOGICAL STUDY OF THE MOLLUSCAN FAUNA ON INTERTIDAL ARTIFICIAL ROCKY SHORE OF TARKWA BAY AREA, LAGOS, NIGERIA
BY
ERUTEYA, ONOSIVBAKPO JONATHAN
`
FEBRUARY 2014
II
ECOLOGICAL STUDY OF THE MOLLUSCAN FAUNA
ON INTERTIDAL ARTIFICIAL ROCKY SHORE OF
TARKWA BAY AREA, LAGOS, NIGERIA
A thesis submitted for the degree of Doctor of Philosophy (Marine Biology)
BY
ERUTEYA, ONOSIVBAKPO JONATHAN
B.Sc, M.Sc (Zoology) Lagos.
MATRIC NO: 830809031
DEPARTMENT OF MARINE SCIENCES
III
IV
DEDICATION
This project is dedicated to Almighty God for His divine guidance over my life, and members of my immediate family.
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ACKNOWLEDGEMENTS
I am indeed grateful for the help and supports I received from numerous people in various institutions during the course of this project. Firstly, I would like to thank my supervisors:
Associate Professor Clement Aghatise Edokpayi for his kindness, thoughtfulness, sense of humour and generous support, which made the work for this study more pleasurable. His sharing of ideas has been and will, hopefully, continue to be one of my most enjoyable experiences.
Again, I would also like to thank my second supervisor, Associate Professor J. K Saliu, who also supervised my M.Sc. thesis. Both of them have supported me throughout, and provided me with sound advice and opportunities that broaden my horizon.
I would like to thank Professors: K. K Ikusemiju, D. I. Nwankwo, Rosemary Egonmwan, and
L. O. Chukwu for their generous supports, for editing of my thesis, award of Graduate Fellow
Scholarship and provisions of scientific journals. They have also continually showed immense optimism and unswerving faith in my abilities.
Thanks to Dr (Mrs) A.O. Osibona, Dr S.O. Ayoola, Dr A.A Otitoloju, Dr A. Z. Aderolu, Dr
(Mrs) A. O. Lawal-Are, Dr M. P. Kuton, Dr I. C. Onyema, Dr Efe Uwadia, Dr M O Lawal and Dr Segun for their friendly supports and encouragement. I would also like to thank the non-teaching staff: Mrs Olutimilehin, Mr Lawal, Mr Coker (Marine Sciences) and Mr
Bengusa (Chemistry Department), Mr Uncle B, a retired Laboratory Technologist (Zoology
Department).
I, also extend my appreciation to my fellow Ph.D students: especially Mr Joseph Nkwoji, and Mr Uzoh (Marine sciences) for their moral support.
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Finally, I would also like to extend my appreciation to all members of my family, more importantly my children (Emmanuel, Josephine and Deborah), they are wonderful team. I cherish their faith in me. I also cherish the love and support of my wife, Mrs Eunice Esther
Eruteya, during the course of this project. This thesis is dedicated to her and my children.
Above all, I thank the Almighty God for His strength and Mercy upon my life without which
I can do nothing (Luke 1:37).
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TABLE OF CONTENTS
CONTENTS PAGES
CERTIFICATION………………………………………………………………………. .II
DEDICATION…………………………………………………………………………... 11I
ACKNOWLEDGEMENTS……………………………………………………………….1V
TABLE OF CONTENTS………………………………………………………………….V1
LIST OF TABLES……………………………………………………………………...... XIV
LIST OF FIGURES…………………………………………………………………….XV1II
LIST OF PLATES……………………………………………………………………..XX111
LIST OF APPENDICES…………………………………………………………………XXV
OPERATIONAL DEFINITION OF TERMS…………………………………………XXXII
LIST OF ABBREVIATIONS…………………………………………………………XXXIII
ABSTRACT…………………………………………………………………………...XXXIV
CHAPTER ONE
I.0 INTRODUCTION…………………………………………………………………..1
1. I BACKGROUND OF THE STUDY…………………………………………..1
1. 2 STATEMENT OF PROBLEM……………………………………………….5
1. 3 AIM AND SPECIFIC OBJECTIVES OF STUDY……………………...... 6
1. 4 SIGNIFICANCE OF THE STUDY…………………………………………..7
1. 5 RESEARCH QUESTIONS………………………………………………...... 8
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CHAPTER TWO
2. 0 LITERATURE REVIEW………………………………………………………….9
2. 1 PHYSICO-CHEMICAL CHARACTERISTICS……………………………..9
2. 2 ROCKY SHORES: ENVIRONMENTAL CONDITIONS………………….11
2. 3 MOLLUSCAN COMMUNITIES AND ADAPTATIONS……………….....11
2. 4 INVERTEBRATE COMMUNITIES OF LAGOS HABOUR AND
GULF OF GUINEA………………………………………………………….12
2.5 BIOLOGY OF INTERTIDAL MOLLUSCS………………………………..13
2.5.1 Feeding………………………………………………….….…….13
2.5.2 Gut Content Analyses………………………………………...... 13
2.5.3 Growth of Intertidal Molluscs…………………………………...14
2.5.4 Heavy metal concentrations: seawaters, seaweeds and
and selected molluscs……………………………………………16
2.5.5 Reproduction in intertidal molluscs…………………………….18
2.6 EFFECT OF PHYSICAL AND PHYSIOLOGICAL STRESS ON
THE DISTRIBUTION OF INTERTIDAL MOLLUSCS…………………...19
2.6.1 Effect of sea surface temperature (SST) on intertidal
molluscs………………………………………………………….21
2.6.2 Ecological Implications of shore Height on molluscs…….……..22
2.6.3 Ecological Effects of Shell Size and Shape of Intertidal
molluscs……………………………………………………...... 24
2.6.4 Ecological Implications of molluscan faunal shell
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colours…………………………………………………………...25
2.6.5 Economic Importance of Intertidal Molluscs……………………26
2.6.6 Strategies for molluscan conservation and sustainable
utilization………………………………………………………….29
CHAPTER THREE
3.0 MATERIALS AND METHODS……………………………………………………31
3.1 DESCRIPTION OF THE STUDY AREA……………………………………..31
3.1.1 West mole………………………………………………………………33
3.1.2 Training mole……………………………………...... 35
3.1.3 East mole………………………………………………………………37
3.2 SAMPLING DESIGN………………………………………………………….39
3.2.1 Site selections………………………………………………………...39
3.2.2 Collection of seawater………………………………………………...44
3.2.3 Collection of algal samples…………………………………………...44
3.2.4 Collection of molluscan samples……………………………………..44
3.2.5 Choice of study species………………………………………………..45
3.2.6 Sample preservations………………………………………………….46
3.3 SAMPLE ANALYSES……………………………………………………………46
3.3.1 Water analyses………………………………………………………....46
3.3.2 Air and Water Temperatures…………………………………….…….46
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3.3.3 Rock Temperature…………………………………………………...... 46
3.3.4 Salinity……………………………………………………………...... 46
3.3.5 Dissolved Oxygen (DO)…………………………….………………….46
3.3.6 Rainfall Data…………………………………………………………...47
3.4 LABORATORY ANALYSIS………………………..…………………………..47
3.4.1 Nutrient Analyses…………………………………………………....47
3.4.2 Heavy metal analysis………………………………………………..47
3.5 STUDIES ON THE BIOLOGY OF INTERTIDAL MOLLUSCS…………. …48
3.5.1 Feeding in selected intertidal molluscan species…………. ………...48
3.5.2 Foraging behaviours of intertidal molluscs………… ………………...48
3.5.3 Gut Content Analysis……………… ………………………………....49
3.5.4 Comparative studies on growth of selected molluscan species at three
different tidal zones…………………………………………………...49
3.5.5 Determination of wet, dry biomass and Ash-free Dry-
Weight (AFDW)………………………………………………………50
3.5.6 Effects of interspecific competition on molluscs’ growth rate
in the laboratory………………………………………………………50
3.5.7 Studies on shell dimensions of selected molluscs……………………51
3.5.8 Studies on the reproductive biology of selected molluscs………….....51
3.5.8.1 Gonadosomatic Index (GSI)……………………….....52
3.5.8.2 Reproductive Effort (R.F)……………….…………….53
3.5.8.3 Histology of the gonads of selected molluscs….. …53
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3.5.8.4 Sex Ratios…………………………………………….54
3.5.8.5 Size at first sexual maturity…………………………..54
3.6 Statistical Analysis……………………………………………………54
3.6.1 Molluscan Data analysis………………………………………………..55
CHAPTER FOUR
4. 0 RESULTS……………………………………………………………………………...57
4.1 PHYSICO-CHEMICAL CHARACTERISTICS OF TARKWA BAY…..57
4.1.1 Temperature……………………………………………………………………57
4.1.2 Salinity and Rainfall Patterns………………………………………………....67
4.1.3 Hydrogen Ion Concentration (pH)…………………………………..……….69
4.1.4 Dissolved Oxygen (DO)……………………………………………………..70
4.1.5 Biochemical Oxygen Demand (BOD)5………………………………… ….72
4.1.6 Chemical Oxygen Demand………………………………………………….74
4.1.7 Conductivity…………………………………………………………………76
4.1.8 Nutrients………………………….…………………………………………77
4.1.9 Heavy metals……………………………………………………………….80
4.2.0 ENVIRONMENTAL FLUCTUATIONS IN INTERTIDAL
ROCK POOLS OF TARKWA BAY……………………………………..………82
4.2.I Thermohaline fluctuations in three different intertidal
rock pools at Tarkwa Bay………………………….……...... 82
4.2.2 Thermal variations in air, rock surface and limpet´s
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foot…………………………………………………………..85
4.3.0 HEAVY METAL STUDIES……………………………………………………...86
4.3.1 Heavy metal concentrations in seawaters, seaweeds,
and selected molluscs…………………….…………………...87
4.3.2 Heavy metal concentrations in different body parts of
molluscs……………………………………………..……….90
4.4.0 COMPOSITION, DISTRIBUTION, ABUNDANCE, DIVERSITY AND
SEASONALITY OF MOLLUSCAN COMMUNITIES OF TARKWA
BAY INTERTIDAL ROCKY SHORE……………………………………..…….108
4.5.0 UNIVARIATE ANALYSIS OF MOLLUSCAN ECOLOGY AT THREE
MOLES OF TARKWA BAY………...... 129
4.5.1 Shannon´s Index (H’)………………………………………………...... 129
4.5.2 Pielou’ Evenness (J’)………………………………………….…...... 132
4.5.3 Simpson’ Dominance Index…………………………………………...... 135
4.5.4 Size- frequency distributions of selected molluscs…..…………………138
4.5.4.1 Patella safiana…………………………………………….....138
4.5.4.2 Nerita senegalensis………………………………………...... 138
4.5.4.3 Thais callifera…………………………………………………139
4.5.4.3 Buccinum undatum…………………………………………..139
4.6.0 BIOLOGY OF INTERTIDAL MOLLUSCS……………………………….…….145
4.6.1 Studies on shell dimensions on selected molluscs……………………145
4.6.2 Gut Content Analysis………………………………………………….168
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4.6.3 Foraging behaviours of selected intertidal molluscs………………….170
4.6.4 Studies on molluscs’ growth at different tidal zones……. ………….172
4.6.5. Effects of intra-and interspecific competitions on growth
rate of selected species at different environments………. ………..174
4.6.6 Growth rates between males, females and in comparison
to a mixed sex molluscan populations……………………… .. …….175
4.7.0 BIOMASS STUDIES ON INTERTIDAL MOLLUSC OF
ECONOMIC INTEREST……………………………………………………177
4.7.1 West mole: Wet Biomass studies………………………………….177
4.7.2 West mole: Dry Biomass studies………………………………. …178
4.7.3 Training mole: Wet Biomass studies……………………………...179
4.7.4 Training mole: Dry Biomass studies…………...... 179
4.7.5 East mole: Wet biomass studies………………………………….180
4.7.6 East mole: Dry biomass studies………………...... 181
4.7.7 Comparison of wet and dry biomass of the three moles…………182
4.8.0 REPRODUCTION IN SELECTED INTERTIDAL MOLLUSCS……………….189
4.8.1 Gonado somatic Index (GSI) in Patella safiana…………………189
4.8.2 Sex Ratio in Patella safiana………………………………………190
4.8.3 Reproductive efforts (RE)……………….……………………...... 191
4.8.4 Gonadosomatic Index (GSI) in Nerita senegalensis……………...193
4.8.5 Sex Ratio in Nerita senegalensis………………………………….194
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4.8.6 Reproductive Effort (R.E) in Nerita senegalensis………………..196
4.8.7 Size at sexual maturity……………………………………………..198
CHAPTER FIVE
5.0 DISCUSSION…………………………………………………………………. …....199
CHAPTER SIX
6.0 SUMMARY AND CONCLUSION……………………………………………… …215
6.1 SUMMARY OF RESEARCH FINDINGS…………………………………...215
6.2 RECOMMENDATIONS…………………………………………………….216
6.3 CONTRIBUTIONS TO KNOWLEDGE………………….…………………218
6.4 CONCLUSION……….………………………………………………………219
REFERENCES…………………………………………………………………………….221
APPENDICES……………………………………………………………………………..246
LIST OF TABLES
CONTENTS PAGES
Table 1: GPS locations of 12 sampling stations and their co-ordinates at the three
moles of Tarkwa Bay……………………………………………………………40
Table 2: Ecological features of the sampling stations at the three moles XV
of Tarkwa Bay……………………………………………………………………..41
Table 3: Temporal variations in physico-chemical parameters investigated in the dry
season at the three moles of Tarkwa Bay…………………………………………59
Table 4: Temporal variations in physico-chemical parameters investigated in rainy
season at the three moles of Tarkwa Bay ………………………………………..60
Table 5: Correlation between physico-chemical parameters of the study stations
of the West mole of Tarkwa Bay……………………………………………….61
Table 6: Correlation between physico-chemical parameters of the study stations
of the Training mole of Tarkwa Bay………………………………………….62
Table 7: Correlation between physico-chemical parameters of the study stations
of the East mole of Tarkwa Bay……………………………………………….63
Table 8: Mean seasonal concentration of heavy metals in seawater, seaweed
and Patella safiana at the Training and West mole of Tarkwa Bay………88.
Table 9: Concentrations of heavy metals in different body parts of the
selected molluscan species investigated during the rainy season………….106
Table 10: Concentrations of heavy metals in different body parts of the
selected molluscs during the dry season…………………………………..107
Table 11: Composition, distribution, abundance, diversity and seasonality of
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molluscan communities of the three moles of Tarkwa Bay……………….120
Table 12 Summary of seasonal variations in the number of individuals
recorded at the three moles of Tarkwa Bay………………………………..126
Table 13: Variations in the number of species recorded during the dry season at
the 3 moles of Tarkwa Bay…………………………………………………127
Table 14: Variation in the number of individuals recorded during the rainy season at the
3 moles of Tarkwa Bay………………………………………………………128
Table 15: Description of shell variables for Nerita senegalensis, Thais callifera
Buccinum .undatum…………………………………………………………145
Table 16: Descriptive statistics for Ash-free-dry Weight (AFDW)
and corresponding Shell length of Buccinum undatum (N=70)………….149
Table 17: Correlation between Log-transformed values of Ash-Free-Dry-Weight
(AFDW) against Shell Length (SL) for Buccinum undatum. Re-
Transformed value of AFDW and SL are provided in the form of a
conventional Allometric equation: W =aLb………………………………149
Table 18: Correlation between Log-transformed values of Ash-Free –Dry-Weight
(AFDW) against shell-length (SL) for Thais callifera. Retransformed
values of AFDW and SL are provided in the form of a conventional
XVII
allometric Equation: W = aLb……………………………………………155
Table 19: Correlation between Log-transformed values of Ash-Free-Dry-Weight
(AFDW) against shell length (SL) for Nerita senegalensis. Re-transformed
values of AFDW and SL are provided in the form of a
conventional Allometric equation W =aLb……………………………….161
Table 20: Laboratory observations on the feeding rates of two
herbivorous limpet……………………………………………………167
Table 21: Summary of mean values of foraging parameters for parameters for
Patella safiana during the dry and rainy seasons………………………..171
Table 22: Temporal variations in wet biomass (gm/m2) of ten dominant species of
molluscan fauna for laboratory analyses from the West mole……………183
Table 23: Temporal variations in dry biomass (gm/m2) of ten dominant species of
molluscan fauna for laboratory analyses from the West mole……………184
Table 24: Temporal variations in wet biomass (gm/m2) of ten dominant species of
molluscan fauna for laboratory analyses from the Training mole………185
Table 25: Temporal variations in dry biomass (gm/m2) of ten dominant species of
molluscan fauna for laboratory analyses from the Training mole …….186
Table 26: Temporal variations in wet biomass (gm/m2) of ten dominant species of
XVIII
molluscan fauna for laboratory analyses from the East mole……………187
Table 27: Temporal variations in dry biomass (gm/m2) of ten dominant species of
molluscan species fauna for laboratory analyses from the East mole…….188
Table 28: The estimated proportion of male and female Patella safiana in monthly
samples from the West mole of Tarkwa Bay ……………………………190
Table 29: Monthly reproductive effort of Patella safiana…………………………..192
Table 30: The estimated proportions of male and female Nerita senegalensis in
monthly samples from the West mole of Tarkwa Bay…………………..195
Table 31: Mean reproductive effort (RE) for male and female Nerita senegalensis
from the West mole of Tarkwa Bay……………………...... 197
LIST OF FIGURES
CONTENTS PAGE
Figure 1: Map of the study areas showing the three moles of Tarkwa Bay…………….32
Figure 2: Temporal variations in Air temperature at the three moles of Tarkwa bay ……64
Figure 3: Temporal variations in Water temperature at the three moles of Tarkwa Bay...65
Figure 4: Temporal variations in Rock temperature at the three moles of Tarkwa Bay …66
Figure 5: Variation of molluscan density with rainfall and salinity………………………68
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Figure 6: Temporal variations in salinity at the three moles of Tarkwa Bay……………..69
Figure 7: Temporal variations in pH at the three artificial breakwaters of Tarkwa Bay…..70
Figure 8: Temporal variations in Dissolved Oxygen (DO) at the three moles
of Tarkwa Bay………………………………………………………………….71
Figure 9: Temporal variations in Biochemical Oxygen Demand (BOD5) at the three
moles of Tarkwa Bay ………………………………………………………...73
Figure 10: Temporal variations in Chemical Oxygen Demand (COD) at the three
moles of Tarkwa Bay………………………………………………………….75
Figure 11: Temporal variations in Conductivity (µS/cm) at the three moles of
Tarkwa Bay ……………………………………………………………76
2= Figure 12: Temporal variations in Nutrient (Sulphate-SO4 ) at the three moles
of Tarkwa Bay……………………………………………………………….79
Figure 13: Temporal variations in nutrients (Phosphate-Phosphorus: PO4-P) at the
three moles of Tarkwa Bay………………………………………………….80
Figure 14: Temporal variations in Nutrients (Nitrate: NO3-N) at the three moles
of Tarkwa Bay (April, 2008- March, 2010)………………………………81
Figure-15 Diurnal variations in temperature at three Rock pools at 3 different tidal
zones in the West mole of Tarkwa Bay…………………… …………………83
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Figure-16 Diurnal variations in salinity at three rock pools at 3 tidal zones
at the West mole of Tarkwa Bay……………………………………………..84
Figure-17 Temporal variations in Air, rock pool, rock surface and limpet temperature
at the tidal zones at the West mole of Tarkwa Bay………………………..86
Figure - 18 Mean seasonal variations of heavy metals in different body parts of
Nerita senegalensis……………………………………………………….91
Figure-19 Mean seasonal variations of lead in different body parts of
Nerita senegalensis……………………………………………………………92
Figure-20 Mean seasonal variations of zinc in different body parts of
Nerita senegalensis ………………………………………………………93
Figure-21 Mean seasonal variations of Manganese in different body parts of
Thais callifera……………………………………………………………….94
Figure-22 Mean seasonal variations of lead in different body parts of
Thais callifera………………………………………………………………95
Figure-23 Mean seasonal variations of chromium in different body parts of Thais
Callifera…………………………………………………………………………….96
Figure-24 Mean seasonal variations of Iron in different body parts of
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Thais callifera………………………………………………………………………97
Figure-25 Mean seasonal concentrations of zinc in different body parts of
Thais callifera………………………………………………………………...98
Figure-26 Mean seasonal concentrations of copper in different body parts of
Thais callifera……………………………………………………………….99
Figure-27 Mean seasonal concentrations of Manganese in different body parts of
Buccinum undatum …………………………………………………………100
Figure-28 Mean seasonal concentrations of lead in different body parts of
Buccinium undatum………………………………………………………………..101
Figure-29 Mean seasonal concentrations of chromium in different body parts of
Buccinium undatum……………………………………………………102
Figure-30 Mean seasonal concentrations of Iron in different body parts of
Buccinium undatum……………………………………………………103
Figure-31 Mean seasonal variations of zinc in different body parts of
Buccinum undatum…………………………………………………….104
Figure-32 Mean seasonal concentrations of copper in different body parts of
Buccinium undatum……………………………………………………..105
Figure-33 Effects of rainfall on salinity at the three moles of
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Tarkwa Bay……………………………………………………………..109
Figure-34 Mean number of molluscan species /m2 recorded at the three moles
of Tarkwa Bay…………………………………………………………110
Figure-35 Mean number of molluscan species/m2 at the Training mole …………111
Figure-36 Mean number of molluscan species/m2 of East mole …………………..112
Figure-37 Mean number of molluscan individual/m2 at West mole ……………….113
Figure-38 Mean number of molluscan individuals/m2 at the Training mole………..114
Figure-39 Mean number of molluscan individuals/m2 at the East mole …………..115
Figure: 40 Temporal variations in Shannon Wiener Index (H1) computed for
the three moles of Tarkwa Bay…………………………………………116
Figure -41 Temporal variations in Dominance Index (C) computed for the three
moles of Tarkwa Bay……………………………………………………117
Figure-42 Temporal variations in Evenness Index (J1) computed for the three
of Tarkwa Bay …………………………………………………………….118
Figure-43 Temporal variations in Shannon’s Index at 12 sampled stations of the three
moles of Tarkwa Bay ……………………………………………………..131
Figure-44 Temporal variations in Evenness Index computed for12 sampled
stations at the three moles of Tarkwa Bay………………………………..134
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Figure-45 Temporal variations in Simpson’s Index at 12 sampled stations for the
three moles of Tarkwa Bay ……………………………………………..137
Figure-46 Size-frequency distribution of Patella safiana at the three
moles of Tarkwa Bay…………………………………………………...140
Figure-47 Size-frequency distributions of Nerita senegalensis at the three
moles of Tarkwa Bay…………………………………………………….141
Figure-48 Size-frequency distribution of Thais callifera at the three
moles of Tarkwa Bay………………… ………………………………..143
Figure-49 Size-frequency distributions of Buccinum undatum at the three
of Tarkwa Bay………………………………………………………….....144
Figure-50 Shell dimensions of Buccinum undatum…………………………………..145
Figure-51 Shell dimensions for Thais callifera……………………………………....146
Figure-52 Shell dimensions for Nerita senegalensis………………………………….147
Figure-53 Relationship between Log Ash-Free-Dry-Weight (AFDW) and Log Shell
Length (SL) in Buccinum undatum……………………………………….150
Figure-54 Shell variables relationships for shell length Vs. shell width for
Buccinum undatum ……………………………………………………..151
Figure-55 Shell variable relationships for shell height Vs. in Buccinum undatum…..152
XXIV
Figure-56 Shell variable relationships for shell length Vs. Aperture length in
Buccinum undatum……………………………………………………….153
Figure-57 Shell variable relationships for aperture length Vs aperture width in
Buccinum undatum……………………………………………………….154
Figure-58 Relationship between Log Ash- Free-Dry-Weight (AFDW) and Log Shell
Length (SH) in Thais callifera…………………………………………….155
Figure-59 Shell variable relationship for shell length Vs shell width for
Thais callifera…………………………… ……………………………….156
Figure-60 Shell variable relationships for shell length Vs aperture width in
Thais callifera…………………………………………………………….157
Figure-61 Shell variable relationships for shell length Vs Aperture length for
Thais callifera………………………………………………………………158
Figure-62 Shell variable relationships for shell length Vs shell height in
Thais callifera………………………………………………………………………..159
Figure-63 Shell variable relationships for Aperture length Vs aperture width in
Thais callifera………………………………………………………………160
Figure-64 Relationship between Log Ash-Free-Dry-Weight (AFDW) and Log Shell
Length (SL) in Nerita senegalensis……………………………………….161
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Figure-65 Shell variables relationships shell length Vs shell height for
Nerita senegalensis………………………………………………………..162
Figure-66 Shell variable relationships for shell length Vs shell height for
Nerita senegalensis………………………………………………………………….163
Figure-67 Shell variable relationships for shell length Vs shell width for
Nerita senegalensis…………………………………………………………..164
Figure-68 Shell variable relationships for shell length Vs aperture width in
Nerita senegalensis………………………………………………………..165
Figure-69 Shell variable relationships for shell length Vs aperture width for
Nerita senegalensis……………………………………………………….166
Figure-70 Mean Percentage of different algae and detritus found in the gut content of
Limpet species……………………………………………………………...168
Figure-71 Box-plot showing the minimum, mean and maximum percentage of gut
contents of limpet species………………………………………………….169
Figure- 72 Mean monthly increment in Shell Length (SL) in cohort of
Patella safiana……………………………………………..……………….172
Figure-73 Mean monthly increment in Shell Length (SL) in cohort of
Nerita senegalensis...... 173
XXVI
Figure-74 Variations in Shell Length (SL) increment in Tank 1 Patella safiana and
Tank 2 (Patella safiana+ Nerita senegalensis)………………………….174
Figure-75 Mean shell length increment in population of Patella safiana………….176
Figure-76 Mean wet weight increment in population of Patella safiana…………….177
Figure-77 Temporal variations GSI values for male and female of Patella safiana….189
Figure-78 Temporal variations in GSI values for male and female of
Nerita senegalensis………………………………………………………194
LIST OF PLATES
CONTENTS PAGES
Plate-1 West mole of Tarkwa Bay…………….……………………………………….34
Plate-2 Training mole of Tarkwa Bay………………………………………………….36
Plate-3 East mole of Tarkwa Bay………………………………………………………38
Plate-4 Station 1 at the West mole of Tarkwa Bay……………………………………..41
Plate-5 Station 2 at the West mole of Tarkwa Bay……………………………………41
Plate-6 Station 3 at the West mole of Tarkwa Bay……………………………………...41
XXVII
Plate-7 Station 4 at the West mole of Tarkwa Bay…………………………………….. 41
Plate-8 Station 1 at the Training mole of Tarkwa Bay… ……………………………...42
Plate-9 Station 2 at the Training mole of Tarkwa Bay………………………………….42
Plate-10 Station 3 at the Training mole of Tarkwa Bay………………………………….42
Plate-11 Station 4 at the Training mole of Tarkwa Bay………………………………….42
Plate-12 Station 1 at the East mole of Tarkwa Bay………………………………………43
Plate-13 Station 2 at the East mole of Tarkwa Bay……………………………………….43
Plate-14 Station 3 at the East mole of Tarkwa Bay…….………………………………. ..43
Plate-15 Station 4 at the East mole of Tarkwa Bay………………………………………43
Plate-16 Study species (A= Thais callifera, B = Patella safiana,
C = Nerita senegalensis and D = Buccinum undatum……………………..….. 45
LIST OF APPENDICES
CONTENTS PAGES
Appendix 1: Physico-chemical parameters investigated at the West mole of Tarkwa
Bay (April, 2008-March, 2010)…………………………………………….246
Appendix 2: Physico-chemical parameters investigated at the Training mole of Tarkwa Bay
(April, 2008-March, 2010)………..……………………………………….247
Appendix 3: Physico-chemical parameters investigated at the East mole XXVIII
of Tarkwa Bay (April, 2008 – March, 2010………………………………..248
Appendix 4: Descriptive statistics for number of individuals collected in dry seasons
at the three moles of Tarkwa Bay (April, 2008 – March, 2010)…………249
Appendix 5: Temporal variations in euryhaline molluscan species sampled at
the three moles of Tarkwa Bay (April,2008-March, 2010)………………251
Appendix 6: Temporal variations in dry season molluscan species sampled at
the three moles of Tarkwa Bay(April, 2008-March, 2010)...... 252
Appendix 7: Temporal variations in rainy season molluscan species sampled at
the three moles of Tarkwa Bay (April, 2008- March, 2010)………..…..253
Appendix 8: Checklist of common molluscan species of the three moles
of Tarkwa Bay (April,2008–March,2010)……………………………..254
Appendix 9: Checklist of rare species of molluscan communities of Tarkwa Bay
(April, 2008 – March, 2010)……………………………………………..255
Appendix 10: Checklist of molluscan ornamental species of the three moles
of Tarkwa Bay ( April 2008- March, 2010)…………………………..256
Appendix 11: Checklist of species of aquaculture potentials sampled at the three
moles of Tarkwa Bay (April, 2008 – March, 2010)…………………….257
Appendix 12: Checklist of bio-fouling species of the molluscan communities of
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Tarkwa Bay (April, 2008-March, 2010 )………………………………258
Appendix 13: Descriptive statistics for the number of individuals collected at the
three moles of Tarkwa Bay during the dry season
(2008-March, 2010) ……………………………………………………...259
Appendix 14: Descriptive statistics for the number of individuals collected at the
three moles of Tarkwa Bay during the rainy season
(April, 2008- March, 2010)………………………………………………261
Appendix 15: Temporal variations in total abundance, compositions, distributions of
molluscan faunal species the three tidal zone among the three
moles of Tarkwa Bay (April, 2008 – March, 2010)……………………263
Appendix 16: Mean values of male and female monthly gonad dry weight (mg) of
three species of herbivorous gastropods investigated from( May,2008
-December, 2009)………………………………………………………….264
Appendix 17: Temporal variations in Species Richness (d) computed for the communities
of molluscan fauna sampled at the three moles of Tarkwa Bay
(April, 2008 – March, 2010)………………………………………………265
Appendix 18: Temporal variations in Shannon – Weaver Indices computed for the
communities of the molluscan fauna investigated at the three
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moles of Tarkwa Bay ( April, 2008 – March, 2010……………………..266
Appendix 19: Temporal variations in Simpson’s Dominance Index (C) computed for
the communities of the molluscan fauna at the three moles
of Tarkwa Bay (April, 2008 – March, 2010 )…………………………….267
Appendix 20: Temporal variations in values of Evenness Indices computed for the
communities of the molluscan fauna at the three moles
of Tarkwa Bay (April,2008- March ,2010 )……………………………268
Appendix 21: Temporal variations in density ( Total number of Individuals/m2) of
different species of molluscan fauna collected at the 3 moles
of Tarkwa Bay ( April,2008- March, 2010)……………………………..269
Appendix 22: Temporal variations in number of individuals’ molluscan fauna
sampled at the three tidal levels at the three moles of Tarkwa Bay
(April, 2008 – March, 2010)……………………………………………..270
Appendix 23: Temporal variations in the number of species ( S ) computed for the
communities of molluscan fauna sampled at the three moles
of Tarkwa Bay ( April,2008 – March, 2010 )………………………………272
Appendix 24: Studies on the growth of Patella safiana in the natural and the laboratory
environments investigated (May, 2008- July, 2009) on the East mole of
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Tarkwa Bay………………………………………………………………..273
Appendix 25: Temporal variations of heavy metal (µg/g/dry weight) concentrations
- in different body parts of selected molluscan faunal species at
the west mole, investigated in dry season (April, 2008-March, 2010)….274
Appendix-26 Temporal variations of heavy metal concentration (µg/g dry weight)
in different body parts of selected molluscan species in the West
mole investigated in rainy season (April,2008- March, 2009)………275
Appendix-27 Mean concentrations of heavy metals in seawaters, seaweeds and selected
molluscan species investigated at the three mole of
Tarkwa Bay in Dry season ( April, 2008- March, 2010),………………276
Appendix-28 Mean concentrations of heavy metals in seawaters, seaweeds and selected
molluscan species investigated at the three moles of
Tarkwa Bay in dry season (April, 2008- March, 2010)………………..277.
Appendix-29 Mean concentration of heavy metals in seawater, seaweeds and
selected molluscan species investigated in rainy season at the three moles
of Tarkwa Bay…………………………………………………………278.
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1.6 Operational definition of terms:
• Anthropogenic - Human induced environmental degradation conditions of a community
or ecosystem.
• Artificial breakwaters - are heterogeneous rocky assemblages built to abate
erosion along the coastline.
• Baseline - Historical data taken to assess the current conditions of a community or
an ecosystem.
• Bay: Part of the sea within a wide curve of the shore.
• Dominant species- Organism that exerts a controlling influence on or define the character of a community.
• Fauna: Animal community found in one or more regions.
• Foraging- Act of acquiring food for optima energy expenditure.
• Intertidal -Alternately flooded and exposed by tides.
• Quadrat- A rectangular or squared-shaped instruments used to estimate density cover and biomass of both plant and animals.
• Reference site -A minimal impaired site that is representative of the expected ecological conditions and integrity of other of the same type and region.
• Regime – A regular pattern of occurrence or action.
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1.7 Lists of Abbreviations
WM West Mole (West artificial breakwaters).
TM Training Mole
EM East Mole
ITCZ Inter-Tropical Convergence Zone
GPS Global Positioning System
S. R Sex Ratio
GSI Gonad Somatic Index
R E Reproductive Effort
GW Somatic Weight
SST Sea Surface Temperature
SSS Sea Surface Salinity
AAS Atomic Absorption Spectrophotometer
MFS Millipore Filtering System
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Abstract
The molluscan community living in the three moles of Tarkwa Bay, Lagos was studied monthly between April 2008 and March 2010. These moles are made of rock known as the west, training and east. They provide attachment surfaces for the settlement of littoral communities. The study investigated the physico-chemical parameters, nutrients, heavy metals concentration levels in sea surface water, algae and resident molluscs of the three moles. Molluscan diversity, feeding, guts content analysis; growth and reproduction of selected species were assessed. Water samples were collected monthly at low tides from twelve geo-referenced network of sampling stations established on the littoral shorelines of the study sites. Sea surface water was collected just 0.5 metre below the surface using 2.01 non-metallic Hydrobios water sampler, kept in pre-labelled polyethylene 500ml bottles, and later transported to the laboratory for storage in deep freezer at 40C for further analyses. Algal samples were scraped from rock surfaces at low tides, and washed 3 times in seawaters and kept in pre- labelled 1000ml plastic containers for storage in the laboratory. Molluscs were collected at both subtidal and intertidal using quadrats of inert aluminium frame of size 1 m2 were used at low tides along transects fixed landward-seaward directions at 12 study sites. A total of 8486 individuals belonging to 69 species, 34 families and 4 classes were recorded.
The four classes of Phylum Mollusca encountered were: Gastropoda 89.92%; Bivalvia
9.55%; Cephalopoda 0.3%; and Polyplacophora 0.2%. A total of 5794 individuals constituting 68.3% of the total population, were collected during the dry seasons, compared to 2692 individuals (31.70%) collected during the rainy season. The One - way ANOVA results showed that growth in Patella safiana and Nerita senegalensis were significantly difference among the three tidal zones on the shore (P < 0.05). The annual mean percentage of Chlorophyta in the gut of Patella safiana was 34.3 ± 7.51% with a range of 1.8% (July) to
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44% (May). Rhodophyta had a minimum percentage gut content of 4% (April), reaching a maximum of 31% (July) with a mean percentage gut content of 14.58± 8.43%. Detritus accounted for a minimum of 17% (March) and a maximum of 32% (November) with annual mean value of 23.7 ± 4.31%. The mean value for the level of metal concentrations decreased in the order: Mn > Fe > Zn > Cu > Cr > Pb; in seawater, algae and molluscs. The level of heavy metal concentrations in the body parts of molluscs decreased in the order: Body tissues > foot > mantle > shell. The highest level of metal concentration was recorded in
Buccinum undatum (266.6µg/g dry wt.) for Mn and lowest concentration was found in Nerita
Senegalensis (0.01µg/g dry wt. of Pb).The assessment of Gonadosomatic Index (GSI) in male and female showed similar temporal patterns (t 0.05, 38= 2.02), however, but there was significance different among months (ANOVA; P < 0.05) for reproductive cycles of Patella safiana and Nerita senegalensis. The annual reproductive efforts for patella safiana (0.7048) male and female (0.5360), while Nerita senegalensis male (3.2436) and female (3.0190). The study generated a comprehensive checklist of molluscan communities of Tarkwa Bay which will be useful for future assessments and ecotourism development. Information on water quality, dietary preference and heavy metal concentration will be handy for shellfish industries. The established seasonal influence and reproductive patterns in selected molluscs, which will serve as valuable tools for breeding and conservation of intertidal molluscs in maritime communities in Nigeria.
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