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.