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Zooplankton of the Kenya Coast: ecology and systematics
Osore, M. K. W. (2003). Zooplankton of the Kenya Coast: ecology and systematics. PhD Thesis. Vrije Universiteit Brussel: Brussel. 192 pp.

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Document type: Dissertation

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  • Osore, M. K. W.

Abstract
    The Kenya coast is characterised by the half-year reversing Monsoon winds and by similarly alternating wet and dry seasons, which influence the marine and coastal environment and the flora and fauna therein. The geomorphology of the coastline comprising of creeks, bays and lagoons; and associated with various habitats of mangals, seagrass beds and coral influence the abundance, diversity and distribution of zooplankton (Chapter 1). Physico-chemical variations of the water are confined within narrow ranges except salinity, which is drastically reduced during the wet season. The hydrographical profile, climate and marine habitats of Kenya are presented in Chapter 2 including historical weather records of temperature, rainfall, humidity and evaporation. Research methodologies and material used are presented in Chapter 3. This study reports that zooplankton population off the Kenya coast is rich, comprising more than 300 taxa of commonly occurring holoplankton and meroplankton. The zooplankton abundance varies depending on the season and the prevailing coastal geomorphology. Gazi Bay (Chapter 4) has near pristine conditions due to its location far away from major industries. Mtwapa Creek (Chapter 7) on the contrary is exposed to constant anthropogenic influence it has however, high rates of flushing resulting to efficient water exchange with the open ocean. Mida Creek (Chapter 8) lacks rivers but has substantial groundwater discharge. During the wet season, Gazi Bay and Mtwapa Creek, which have river inlets recorded high zooplankton abundances of up to 2,000 m'3. Mida Creek recorded lower abundance of about 1,000 m‘3 during the wet season, but during the dry season it increased to about 2,800 m'3. The most abundant holoplankton, which accounted for approximately 98 % of this category were Copepoda, Medusae, Chaetognatha, Appendicularia, Foraminifera, Siphonophora, Ostracoda and Cladocera. Holoplankton taxa were consistently abundant in Gazi Bay and the Mombasa Marine Park lagoon with densities ranging from about 500 to 800 m'3. They were moderately abundant in Mtwapa Creek and Mida Creek with approximate densities of between 200 and 600 m'3. They were often less than 200 m3 in Makupa Creek (Chapters 5, 6). This creek is almost completely enclosed, has poor flushing rates and has been subjected to long term dumping of industrial and domestic wastes. Meroplankton was mainly represented by Gastropoda, Brachyura zoea, Caridea, Pisces eggs and larvae, Decapoda and Isopoda. These taxa constituted approximately 77 % of the entire meroplankton category in numbers. They were mostly abundant in Makupa Creek (Chapters 5, 6) where they often occurred in monthly densities of between 200 and 400 m'3 and occasionally more than 2,000 m'J. Copepoda, whose abundance constituted more that 70 percent of the population numerically dominated the zooplankton community. Acrocalanus, Oithona, Acartia, Pseudodiaptomus, Undinula, Corycaeus, Tortanus and Oncaea were the dominant genera and accounted for more than 90% of the total copepod population. Sixteen species of the copepod family Candaciidae were found to occur off the Kenya coast and were most abundant (up to 360 in 100 m3) in the shelf waters (Chapter 9). Candacia bradyi A. Scott, 1902; C. bipinnata Giesbrecht, 1889; C. curta (Dana, 1849), C. tuberculata Wolfenden, 1905 and C. ethiopica (Dana, 1849) were reported as new records for Kenya. New morphological characters were identified and described on specimens of Candaciidae (Chapter 10), which will be valuable in taxonomic studies.

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