Influence of macrofauna on the vertical distribution of meiobenthos in an <i>Avicennia</i> mangal, Gazi Bay, Kenya

The influence was studied in an Avicennia marina mangrove in the upper intertidal zone of Gazi Bay (Kenya), over a period of two months. Exclusions were performed in co-operation with the University of Gent. Cube cages with a bottom surface of one square meter were erected, walled with plastic gauze (mesh-width: 1mm). In order to evaluate possible procedure-effects, partial cages (i.e. cages with the seaward side left open) were placed in the field. Crabs and gastropods were eliminated out of the cages. The meiofaunal component was measured qualitatively and quantitatively. Samples were taken with a handcore (diameter: 36 mm) and fractioned in slices (0-2 cm, 2-4 cm, 4-10 cm and below). Three replica' s were taken from three treatments (cage, partial cage and blanco). The experimental units were placed following a randomized block design. The meiobenthos and some environmental factors (grain size analysis, curtosis, skewness, median particle diameter, porosity, % of organic material, redox potential; temperature, chlorophyl a, fucoxanthine, nutrient analysis, salinity, pH and dissolved oxygen) were sampled before the cages/partial cages were placed in the field, five days and one month after installation. Statistical ANOV A-test was applied to test for significant effects on the environmental factors and the meiobenthos. Only pigments showed a clear increase in the cage in the third sample-period. This was probably due to a bloom of diatoms, and the exclusion of the gastropods can be at the origin of this growth. The meiofauna showed no remarkable exclusion-effects after one month. This can be due to the short sampling period, unknown cage-effects, interactions between the meiobenthos (ex. changes in community species structure) and other non-measured underlying factors or factor-combinations. Three new harpacticoid species (Crustacea, Copepoda, Darcythompsoniidae Lang) from the genus Leptocaris T. Scott (1899) were described and discussed in detail