The project investigated small-scale biotic interactions between laminated microbial communities and meiofauna at light-exposed sediment-water boundaries of estuarine lagoons. The production and biological structure of these systems is mainly determined by complex processes at the sediment-water interface which depend on finely scaled patterns, requiring appreciation of how the biota interact within these scales. We tested whether changing light conditions and active emergence of the harpacticoid species Mesochra lilljeborgi and Tachidius discipes are mediated by the activity of benthic oxygenic and anoxygenic phototrophic microbes. Two hypotheses were tested which addresses to the question of causality between changing light conditions and active emergence of the harpacticoid copepods. (1)The harpacticoid copepods T. discipes and M. lilljeborgi will enter the bottom water during daylight when oxygenic photosynthesis of cyanobacteria and eukaryotic algae is blocked and conditions at the sediment-water interface have turned anoxic. (2)Both species will not emerge during dark exposures when transferred to sterilized sediments.