Combined effects of an antifouling biocide and nutrient status on a shallow-water microbenthic community

The complex systems of shallow-water sediments are today subjected to varying nutri- ent inputs combined with other anthropogenic stressors, such as toxicants. The effects of differences in nutrient status of the sediment combined with short-term, low-level exposure to the anti-fouling biocide copper pyrithione (CPT) were studied in a 38 d experiment using intact sediment in a flow- through mesocosm system. Abundance and diversity of microphytobenthos, bacteria and meiofauna were assessed together with sediment-water oxygen and nutrient fluxes (day and night) and denitri- fication. More effects were found for the sediment with higher nutrient status, but these combined effects could not be predicted by adding the separate effects of nutrients and CPT observed for the sediment with low nutrient status. Biomass and diversity of microphytobenthos increased later on in the experiment due to CPT exposure, as did bacterial activity and abundance. CPT exposure also increased the proportion of nematodes in the meiofauna. Generally, prokaryotic functions appeared more affected by CPT exposure than eukaryotic. Differences in the response of functional variables suggest that eukaryotic photoautotrophs possess a higher functional redundancy than heterotrophs. Among nutrient fluxes the nitrogen cycling was affected through changed rates of ammonium flux and denitrification. The integrated analyses show a clearer effect of CPT on the community structure under low-nutrient status, while CPT affected the community function more in the high-nutrient system. All treatments show convergence of function, in both light and dark, towards the end of the experiment, whereas the structure remained separated due to the nutrient regime.