The infaunal macrobenthos under East African <i>Ceriops tagal</i> mangroves impacted by epibenthos

The interactions between macrobenthic in- and epifauna of a mid-intertidal Ceriops tagal (Perr.) Rob. stand were studied in order to test the relative importance of epibenthic predation pressure on and resource competition with the macro-endobenthos. The study is the fourth in a series of papers based on exclusion experiments in two different parts of the mangrove system at Gazi Bay in southern Kenya. The permanent and visiting epibenthos were excluded using cages. Densities of the macrobenthic taxa Oligochaeta (families Tubificidae and Enchytraeidae), Amphipoda (genera Grandidierella and Ampelisca), Insecta larvae (family Dolichopodidae), Polychaeta (families Nereidae and Terebellidae), macro-Nematoda (family Oncholaimidae), and Gastropoda, and a broad range of the environmental factors were followed over five months of caging. A significant increase of the dominant tubificid population and the polychaete Namalycastis spec. in the cage-covered sediment indicated a positive exclusion effect. The polychaetes seemed to be impacted by epibenthic predation. Resource competition for muddy detritus, however, was evidenced to be the structuring force for the numerically dominant oligochaetes. The bulk of the studied macrobenthic infauna is therefore proposed to be a trophic dead end and to have only a minor interactive position in the mangrove foodweb