Do the presence and physiological stage of algal mats affect the meiobenthic community in a tropical estuary?

The effects of compacted algal mats growing attached to sediments on the abundance and community structure of intertidal sediment meiofauna and harpacticoid copepod assemblages were evaluated on a tropical estuarine mudflat. Differences in fauna based on the presence of algae (within vs. outside the algal patches) and the physiological stages of the algae (live vs. decomposing algal patches) were compared. In general, lower densities occurred within algal patches for most meiofaunal groups, except for harpacticoids, which showed an increase in number in the live algal patches (LAP). Non-metric MDS analysis clearly distinguished both meiofauna community and harpacticoid assemblage in relation to the presence of algae and the physiological stage. Organic matter, carbohydrates, proteins and photosynthetic pigments were higher within algal patches and highly correlated with meiofauna variables. One species of harpacticoid (Cletocamptus sp.1) dominated the LAP samples and thus reduced species richness and diversity of harpacticoids in these samples. The species Robertsonia mourei occurred exclusively in decomposing algal patches (DAP) and probably is an opportunistic species within the DAP samples. Strong differences regarding live and decomposing algae samples highlighted the importance of physiological stage in understanding meiofaunal responses to algal mats.