Benthic microalgae: comparisons of chlorophyll a in mesocosms and field sites

A mesocosm facility is being developed by the CSIRO Division of Fisheries to study the movement, fate and impact of pollutants in coastal marine environments. Initially, we are studying coastal habitats in S.W Australia that are subject to wave action. A 12 week experiment assessed changes in biotic and abiotic components of sediment brought from the field into mesocosms. In these sediments, benthic microalgae are the major primary producers. Microalgal standing stocks were measured as the concentration of chlorophyll a and phaeopigments in the top 2 cm of sediment, and these measures were compared among mesocosms and field sites. Significant increases in chlorophyll a and phaeopigments, increased numbers of species and a shift from episammic to periphytic diatoms were observed, possibly caused by decreased water motion in mesocosms or other containment effects. Results from statistical power analyses suggested that our sampling was sufficiently well replicated and successfully incorporated variation at small spatial and temporal scales. Sampling effort used in this experiment should form the basis for future work with benthic microalgae.