A cage exclusion experiment was used to examine the interaction between the eplbenthos (permanent and vls~tlng) and the macroinfauna of a high intertidal Kenyan Avicennia marina mangrove sediment. Densities of Ollgochaeta (families Tubificidae and Enchytraeidae), Amphipoda, Insecta larvae, Polychaeta and macro-Nematoda, and a broad range of environmental factors were followed over 5 mo of caging. A significant increase of amphipod and insect larvae densities in the cages indicated a positive

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... lusion effect, while no such effect was observed for oligochaetes (Tubificidae in particular), polychaetes or macronematodes. Resource competitive interactions were a plausible explanation for the status of the amphipod community. This was supported by the parallel positive exclusion effect detected for microalgal densities. It is therelore hypothesized that competition for microalgae and deposited food sources is the determining structuring force exerted by the epibenthos on the macrobenthic infauna. However, the presence of epibenthic predation cannot be excluded.