Environmental Factors and Coral Bleaching in Kenya. Item Type Thesis/Dissertation Authors Mdodo, Rennatus Magina Publisher Moi University Download date 09/10/2021 08:50:19 Link to Item http://hdl.handle.net/1834/7779 ENVIRONMENTAL FACTORS AND CORAL BLEACHING IN KENYA MDODO RENNATUS MAGINA (B.Sc.) A thesis submitted in partial fulfilment of the requirements for the degree of MASTER OF PHILOSOPHY IN ENVIRONMENTAL STUDIES (BIOLOGICAL SCIENCES) MOl UNIVERSITY 1999 DECLARATION This thesis is my original work and has not been presented for a degree in any other university. Signature _ Mdodo R. Magina. This thesis has been submitted for examination with our approval as supervisors. Signature-------------------- Prof M. P. Tole Supervisor and Professor ofEnvironmental Geochemistry School ofEnvironmental Studies Moi University. Signature _ Dr. David Obura Supervisor and Research Fellow Coral Reef Conservation Project, Mombasa. Signature _ Dr. Nyawira Muthiga Supervisor and Senior Marine Scientist Kenya Wildlife Service, Mombasa II DEDICATION To my late sisters, Mariam and Zakia, My parents, Raphael and Bilkiss, And my brother FeisaL This work is especially for you. III ACKNOWLEDGEMENT I got the interest to venture into coral reef studies from Dr. Nyawira Muthiga and I thank her for her guidance and encouragement throughout the study. I am grateful to Dr. David Obura for his tireless efforts to see me through the work. He has been my role model in the study of coral reefs. The critical comments, criticism and suggestions from Professor M. P. Tole are highly appreciated. He has always been there for me throughout the study period and for this I say, Thank you. I would like to express my gratitude to Dr. Tim McClanahan of Coral Reef Conservation Project, Dr. J.B. Okeyo of Moi University, School of Environmental Studies and Prof J Hoorweg ofCoast Environment Research Station, Malindi for their comments. I thank the Director, Dr. E. Okemwa, and Staff of Kenya Marine and Fisheries Research Institute, Mombasa, for their support and co-orporation. I greatly acknowledge the skilful technical assistance given by Mr. Kilonzo, Mr. Gonda Mr. Kirnathi and Mr. Mariara, the diver. Gratitude is due to S. Mwangi, D. Kirugara, 1. Mwaluma, C. Migosi and G. Mwatha for helping me so much during data analysis and final write up. I extend my thanks to the staff of Kenya Wildlife Service, Mombasa, and to my dear friends, S.M. Gitahi, K. Lukongodo, M. Kaiga, Veronica, Maureen, Pricilla, Regina and all my SES classmates. They have been very inspirational to me throughout the study. To Ruth, my sweet girl friend thanks for being there when I needed you most. I am indebted to Dr. Ron Johnstone who through the SidaiSAREC Coral Reef Program was able to partly finance this work. Part of this work was also supported by grants from Moi University, Eldoret and Coast Environment Research Station, Malindi. IV \ \ TABLE OF CONTENTS DECLARATION .11 DEDICATION III ACKNOWLEDGEMENT IV TABLE OF CONTENTS V LIST OF FIGURES VII LIST OF TABLES IX LIST OF PLATES X ABSTRACT XI CHAPTER ONE 1 1.0. INlRODUCTION 1 1.I.General 1 1.2 Literature review 3 1.3 Statement of the problem 6 1.4 Research hypotheses 7 1.5 Objectives 7 1.6 Study area 8 1.6.1 General description ofthe kenya coast.. 8 1.6.2 Malindi marine national park 11 1.6.3 Mombasa marine national park 11 1.6.4 Kanamai reef 11 CHAPTER TWO 12 2.0. MATERIALS AND METHODS 12 2.1 Transect surveys for frequency of bleaching 12 2.2 Laboratory measurement ofchlorophyll and zooxanthellae density 12 2.3 Environmental parameters 14 2.3.1 Temperature: 14 2.3.2 Salinity: 14 2.3.3 Suspended sediment: 14 2.3.4 Meteorological data: 15 CHAPTER THREE 16 3.0. RESULTS 16 3.1 Physical parameters..................................................................................... 16 v 3.1. 1 Temperature.......................................................................................... 16 3.1.2 Rainfall 21 3.1.3 Solar radiation 21 3.1.4 Salinity 26 3.1.5 Suspended sediments 26 3.2 Substrate cover 27 3.3 Field measurements of bleaching in mombasa marine national park. 29 3.4 Zooxanthellae density 35 3.5 Chlorophyll measurements 39 3.6 Chlorophyll-a per zooxanthellae 43 3.7 Relationship between water temperature and bleaching 45 3.8 Relationship between zooxanthellae density and diameter of polyp 47 CHAPTER FOUR 50 4.0. DISCUSSION AND CONCLUTIONS 50 4.1. Relationship between environmental parameters and coral bleaching 50 4.1.1 The el nii'i.o effect. 50 4.1.2 Rainfall and sediment impacts 51 4.1.3 Temperature effects 52 4.1.4 Solar radiation effects 54 4.2. Variations in bleaching between species 54 4.3. Zooxanthellae and chlorophyll-a measurements in normal and bleached corals ......................................................................................................................... 55 4.4. Use of zooxanthellae and chlorophyll-a densities to determine extent of bleaching 57 4.5. Community impacts 58 4.6 Conclusion 60 REFERENCES 62 APPENDICES 67 VI LIST OF FIGURES Figure 1:. A map ofKenya showing the study area 10 Figure 2: Variations in daily maximum low tide seawater temperatures for Mombasa MNP, measured by hand held thermometer, between years. Data from 1994-96 was obtained from Obura (1995) 17 Figure 3: Mean monthly sub-surface seawater temperature for Mombasa MNP recorded from August 1996-May 1998. (Source: c.R.c.p temperature loggers, which record hourly temperature readings at the bottom) 18 Figure 4: Variation in mean monthly air temperature in Mombasa between years. (Source: Meteorology Dept, Mombasa) 19 Figure 5: Variation in mean monthly air temperature in Malindi between years. (Source: Meteorology Dept, Malindi) 20 Figure 6: Variation in mean monthly rainfall in Mombasa between years (Source: Meteorology Dept. Mombasa) 22 Figure 7: Variation in mean monthly rainfall in Malindi between years (Source: Meteorology Dept. Malindi) 23 Figure 8: Variations in mean monthly solar radiation (megajoule/m2/day) in Mombasa between years. (Source: Meteorology Dept. Mombasa) 24 Figure 9: Monthly mean air temperatures (DC), solar radiation (Megajoule/m2/day) and rainfall (mm) for Mombasa. The figure compares meteorological data ofprevious El Nmo years to the 1997-98 year. Data was obtained from the meteorology department, Mombasa. (Standard errors could not be obtained) 25 Figure 10: Percent substrate composition in Malindi Marine National Park, Mombasa Marine National Park, and Kanamai (n=1O-12 transects) 28 Figure 11: Field bleaching surveys conducted in Mombasa Marine Park between September 1997 and April 1998. Three species namely, Porites nigrescens, Porites lutea and Pocillopora sp are featured. (N-normal, pbl-partially bleached, bl-bleached, pd-partially dead, d-dead corals, number on each column indicates the sample size) 30 Figure 12: Mean zooxanthellae density between normal and bleached fragments for different species sampled in Mombasa MNP, Malindi MNP and Kanamai. (Number on top ofeach column indicates the sample size) 38 Figure 13: Chlorophyll-a concentration between normal and bleached fragments for different species. (Number on top ofeach column indicates the sample size)...... 42 VII Figure 14: Relationship between Nonnal Porites nigrescens, Porites lutea and Pocillopora sp and mean daily low tide temperature (0 C) in Mombasa marine national park before and during the 1998 coral bleaching event 46 Figure 15: Relationship between the diameter ofthe polyps (mm) and zooxanthellae 2 density (No/cm ) • .............................................................................................. 48 Figure 16: Relationship between the diameter ofthe polyp (mm) and chlorophyll-a 2 concentration (mg/cm ) • •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 49 VIII LIST OF TABLES Table 1: Positive Sea Surface Temperature anomalies from NOAA satellite data along the Kenya coast recorded from September 1997 to July 1998. (Source: NOAA Internet web site) 18 Table 2: Mean salinity measurements (in ppt) in the three study sites 26 Table 3: Mean suspended sediment measurements (in mg/l) in the three study sites. (Sample size for each site =5) 26 Table 4: Substrate composition in the three study sites from data collected in 1996 (Source: C.R.C.P). n = 10-12 transects 27 2 Table 5: Mean zooxanthellae density (Number per cm ) for different coral species in Kanamai, Malindi MNP and Mombasa MNP. % Decrease indicates the density of zooxanthellae lost when the coral bleached 36 Table 6: ANOVA of zooxanthellae densities between species and coral condition (normal and bleached). (r2 = 0.63, n =346) 37 Table 7: ANOVA ofzooxanthellae density between sites (Malindi MNP and Mombasa MNP) and coral condition for Porites lutea (r2 = 0.73, n = 56) 37 Table 8: ANOVA ofzooxanthellae density between sites (Kanamai, Malindi MNP and Mombasa MNP) for Porites nigrescens normal. (r2 = 0.007, n =170) 37 2 Table 9: Mean chlorophyll-a concentration (mg/cm ) for different coral species in Kanamai, Malindi and Mombasa. % Decrease indicates the amount ofpigment lost when the coral bleached 40 Table 10: ANOVA of Chlorophyll-a concentration between species and coral condition (normal and bleached). (r2 = 0.34, n =335) 41 Table 11: ANOVA of chlorophyll-a concentration between site (Malindi MNP and Mombasa MNP) and coral condition for Porites lutea. (r2 = 0.44, n = 56) 41 Table 12: ANOVA of chlorophyll-a concentration between sites (Kanamai, Malindi MJ\TP and Mombasa MNP) for Porites nigrescens normal. (r2 = 0.002, n =183). 41 Table 13: Mean chlorophyll-a concentration per zooxanthellae densities for different coral species in Kanamai, Malindi and Mombasa 44 Table 14: ANOVA of chlorophyll-a per zooxanthellae between species and coral condition (normal and bleached). (r2 = 0.06, n =312) 45 Table 15: Corallite diameter for different species 47 IX LIST OF PLATES Plate 1: Normal (brown in colour) Porites lutea among bleached (white) Porites nigrescens at the starfish point in Mombasa MNP. The picture was taken in April 1998 at low tide using an underwater camera. Massive coral species are more resistant to stress than branching species 31 Plate 2: Bleached porites lutea in Mombasa MNP.