Interactions between epibenthos and meiobenthos in a high intertidal <i>Avicennia marina</i> mangrove forest

Many studies in the muddy intertidal zone of temperate regions have indicated meiofaunal communities to be mainly affected by epibenthic predation and disturbance rather than competition. Few studies, however, have dealt with mangrove sediments of tropical areas. In addition to a parallel study in a Ceriops tagal (Perr.) Rob. zone, a manipulative exclusion technique was used to trace the dominant biological interactions structuring the meiobenthos of an East African Avicennia marina (Forsk.) Vierh. mangrove forest. The densities of the major meiobenthic taxa and nematode genera and a broad range of environmental factors were monitored over a depth profile for one year of caging. Cages (1m²) excluded all epibenthos (>2mm) for one year and were procedurally controlled. Procedural and exclusion effects were traced, using a factorial and mixed ANOVA design. Significant exclusion effects were indicated for oligochaetes and for one of the dominant epistratal feeding nematode genera. They are discussed in terms of epibenthic composition and density, feeding behaviour, food resources, and the abiotic environment. The conclusion is that the observed meiobenthos (especially oligochaetes and nematodes) is influenced mainly by exploitative or resource competition with the epibenthos. The common food source was indicated to be muddy detritus and microalgae. Consequently, the role of the meiobenthos is mainly situated in an isolated, detrital food web with only minor energy fluxes to the epibenthos