A study of the zooplankton of Gazi Bay, Kenya and the adjecent waters: community structure and seasonal variation
Osore, M. K. W. (1994). A study of the zooplankton of Gazi Bay, Kenya and the adjecent waters: community structure and seasonal variation. MSc Thesis. Universiteit Gent: Ghent. 112 pp.
Zooplankton was sampled using the Bongo net of mesh size 335 µm at three stations in Gazi Bay (Kenya 4° 25' S, 39° 50' E). A total of 114 samples were collected alongside environmental variables of temperature, rainfall, salinity, dissolved oxygen, pH and transparency between March 1990 and February 1992. Additional samples were collected on three transects off the Kenyan coast between 19th November and 5th December 1992. All these data were used to assess the Zooplankton community structure, seasonality, distribution and quantity (as dry weight and numbers). A total of 78 copepods species belonging to 44 genera and 28 families were identified in Gazi Bay, two: Pseudodiaptomus marinus and Tortanus murayi appear to be new in the region and two more from genera Clausocalanus and Calanopia may soon be described as new species. 37 main taxonomic groups representing mainly Classes Gastropoda, Bivalvia, Polychaeta and numerous subclasses of Crustacea from both the pelagic and the benthic zones were identified and enumerated in Gazi. Rainfall, tidal regime and transparency were the most important factors affecting the community structure of Zooplankton in Gazi Bay. During the rainy period the numerical abundance increased threefold (from 600 to 1900 ind./m 3) and the biomass of Copepoda more than tripled (from under 2000 to close to 7000 µg D. W./m 3). Oceanic zooplanktonic groups such as Chaetognatha and the Copepoda Acartia spp. were observed to invade the bay during the dry season, and later they were replaced by brackish water types e.g. Pseudodiaptomus spp. in the wet season. Gradients in abundance from the riverine mangrove zone (station 3) to the coraline oceanic zone (station 1) of the bay were displayed by some holoplankton and meroplankton species, but generally little difference in community structure and total Zooplankton abundance between the three stations was observed. This may be due to little difference in environmental variables between stations. The adjacent open ocean was observed to have an equally diverse and abundant Zooplankton community. More diverse and abundant Zooplankton communities were found in the water close to the shore than the water further offshore.
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