Few information is available about the macro-invertebrates of East-Africa and more specific about the epifauna of the East African seagrassbeds. In september 1993 seven stations were sampled in the seagrassbeds of Gazi Bay (Kenya). Three of them are situated in the major western and the small sidecreek and included Cymodocea rotundata and C. serrulata. Three other stations in the major eastern creek include the epifauna of Thalassodendron ciliatum and one T. ciliatum station is situated in the bay. Also the benthos of the seagrassbeds has been studied. A distinction was made between the leafs) the stalks and the roots (bottom) of the seagrasses. The faunal analysis of the epifauna associated with the seagrasses of Gazi Bay showed the Crustacea to be dominant: Amphipoda, Isopoda, Tanaidacea, Cumacea, Copepoda, and Ostracoda are the most important taxa. The Decapoda are represented by very small numbers. Especially the Amphipoda are numerous as epifauna of seagrasses. These six groups of Crustacea has been studied intensively. The animals are, if possible, identified up to the genus-level and a morphological descripition is given. Their occurrence in the study area, Gazi Bay, has been discussed. A key to the genera and families has been made. The table at the end of this summary shows the standardised densities of the six prominent groups of the Crustacea and the total faunal density of the stations, divided in leaf, stalk and roots. The structure of all the epifaunal taxa and the benthos of the seven stations has been investigated by two multivariate analysis techniques, TWINSPAN and CCA. The TWINSPAN-analysis showed a difference between the Cymodocea-community of the western creek and the sidecreek (three stations), the Thalassodendron ciliatum-community of the eastern creek (three stations), and the T. ciliatum-community of the bay (one station). These three communities can also be divided in a leaf-, a stalk-, and a rootgroup. Because of the indecent knowledge of the macro-invertebrates of East-Africa and the limited sampling, at this moment these groups can not be characterised by some typical species associations. Finally the two creeks, following a vegetative study of the eastern creek and the western creek, are comparised by means of densities and standing stocks of the epifauna and the benthos. It seems that the two creeks are quite different. The densities of the epifauna of the western creek (1653 ind/m²) are much lower than those of the eastern creek (21412 ind/m²). The densities of the benthos of the eastern creek (20085 ind/m²), on the contrary, are much lower than those of the western creek (46337 ind/m²); the consequence of these two facts is almost the same total density of macro-invertebrates in both creeks. The standing stocks follow the same trend. An indirect assessment of the standing stock of the eastern creek gives a value between 0,02 and 166 g DW/m², those of the western creek is found between 0,0238 and 192 g DW/m². So, the density of the epifauna of the seagrasses of the eastern creek is much higher than those of the western creek. |
