Ruwa, R.K. (1989). Macrofaunal composition and zonation on sandy beaches at Gazi, Kanamai and Malindi Bay, Kenya. Kenya Journal of Sciences (Series B) 10 (1-2): 31-45

5882

Ruwa, R. K. G.; Kanamai; Malindi, B.; Kenya

1989

10: 1-2

Publication

Based on the crabs which constitute the most conspicuous benthic macrofauna, three biological zones were distinguishable on the Kenyan sandy beaches. These were in a downward shore direction: The Ocypode zone, Dotilla zone and Uca-Macrophthalmus zone which were related to tidal levels, the position of water table and sub-marine groundwater discharge (SGD) or seepage. The Ocypode species which burrow here namely, O. ceratophthalmus, O. ryderi and O. cordimanus. The Dotilla zone extended between MTL and MHWN where the water table was 10-20 cm below the surface of the beach at low tide. The species occupying this zone was almost exclusively Dotilla fenestrata. However, samples of sand collected from the edges of the ebbing and flooding tides were passed through sieve and two species of crabs, Hippa adactyla and Emerita austroafricana, were found. The Uca-Macrophthalmus zone occured between mean tide level (MTL) and mean low water spring (MLWS) where the SGD wetted the biotope throughout the low tide. The Uca species were U. vocans and U. tetragonon. The most common Macropthalmus species were M. grandidieri and M. parvimanus, and the less common ones were M. milloti and M. bosci. There were three species of portunid crabs in the brackish water pools and eight species of gastropods in this zone. In the same zone, the silty sand of Malindi beach had large numbers of Echinodiscus bisperforatus. The present results were compared with those of other parts of the Western Indian Ocean coast and the significance of their similarities and differences is discussed.

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