Advances in Coastal Ecology: people, processes and ecosystems in Kenya

A comparative survey of shallow water (< 2m) holothurian fauna was undertaken to determine patterns of distribution, abundance and diversity, and the possible role of management, habitat (reef flat and lagoon), topographic complexity and substrate cover, in six sites within protected and unprotected reefs near Mombasa. Visual surveys were done by use of belt transects (100m by 4m) and search sampling (1-h time counts), and 10m-line intercept transects for substrate cover and rugosity. A total of ten different species belonging to 2 orders (Aspidochirotida and Apodida) and 3 families (Holothuriidae, Stichopodidae and Synaptidae) were recorded, four most abundant being Holothuria leucospilota, H. atra, Synapta maculata and Stichopus chloronotus in descending order. Three least abundant species were H. hilla, H. impatiens and Stichopus herrmanni. The total holothurians fauna was typified by low densities and high diversity, although no significant differences occurred in diversity (Simpson's Index) between management and habitats. Protected reefs had higher densities on the reef flats and in lagoons than the unprotected reefs. Between-subjects effects analysis indicated that management was more powerful than habitat in controlling holothurian population densities. Rugosity was higher in the MPA than unprotected sites, and there was a positive significant correlation between rugosity and sea cucumber densities and abundance. The nine broad substrate categories indicated high variability between lagoons under different management regimes. Coral cover was higher in protected than unprotected areas, whereas algal turf, sand and seagrass were dominant in the unprotected sites. Hard coral had a positive significant correlation with sea cucumber density, whereas algal turf and sand, showed negative and positive significant correlations respectively. Sand also correlated negatively, but significantly with sea cucumber species diversity. Apart from S. maculata, all the other nine species recorded in the study area have commercial value, varying from medium to low. The overall average density of sea cucumbers of commercial value in the study area was 5.20/400 m2. The most abundant commercial species in the study area was the low value H. leucospilota. Commercial sea cucumber densities in protected and unprotected sites were 11.00/400m2 and 2.30/400m2, respectively. Resource assessment of holothurian populations can be useful for designing, developing and evaluating sea cucumber fishery management plans and strengthening conservation of the resource. Published