BENTHIC MICROALGAE - COMPARISONS OF CHLOROPHYLL-A IN MESOCOSMS AND FIELD SITES

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