Mesoscale effects of aquaculture installations on benthic and epibenthic communities in four Scottish sea lochs

The broad-scale effects of salmon farming on benthic and epibenthic macrofaunal communities of four Scottish sea lochs (Kishorn, Duich, Hourn and Nevis) with different aquaculture loadings were investigated based on the first benthic surveys to be undertaken in these lochs. Significant variation in the benthic communities was identified between lochs, mainly related to differences in the abundance of echinoderms and polychaetes (the dominant components of the benthic communities). Variance partitioning using partial redundancy analysis suggested that approximately 9.6% of this variation could be related to aquaculture activity in the lochs (as expressed through "production" and previously modelled "impact" levels), as compared to 20.6% attributable to measured environmental factors. Epibenthic communities were dominated by echinoderms and arthropods and there was no significant between-loch variation in epibenthic community composition. No significant differences were apparent in the benthic or epibenthic community assemblages between samples taken within 2000 m of a fish farm and those taken beyond this distance. In general, our results support previous studies suggesting a spatially limited impact of salmon culture installations on the benthos, although impacts on the aquatic food web on a wide spatial scale cannot be ruled out and the link between benthic community variation and aquaculture variables identified through variance partitioning requires further investigation.