Spatial variation of benthic infaunal communities in baie de Gaspé (eastern Canada) — Influence of mussel aquaculture

This study examines the effect of mussel farming on benthic infaunal communities in baie de Gaspé, eastern Canada, at two spatial scales: 10 m (directly under vs. between mussel longlines — Position) and 100 m (between mussel farm and reference locations — Treatment, each of which was replicated at 4 Sites). None of the evaluated univariate descriptors of benthic communities (abundance, taxonomic richness, Shannon–Weiner diversity, AMBI, and M-AMBI) differed between Treatments or among Positions within Sites in any consistent way. Similarly, multivariate community structure also did not differ among Treatments. In contrast, multivariate community structure directly under mussel lines differed from that between mussel lines in 3 of 4 mussel farm sites whereas none of the reference sites showed such 10 m-scale variation. Of the species that accounted for the greatest proportion of the dissimilarity between Positions within mussel farm sites, second-order opportunistic species (Prionospio steenstrupi and Pectinaria granulata) were consistently more abundant directly under mussel lines than between them. Species belonging to other ecological groups did not show any consistent trends. It is suggested that studies that do not consider within-site (10 m-scale, below vs. between longlines) variation may fail to detect the influence of suspended bivalve culture in some cases. Overall, effects of mussel culture in baie de Gaspé were slight and within the natural variation of benthic communities in the area. This suggests that the current industry should be sustainable. However, plans to expand the industry in the region remain to be evaluated with respect to the ecological carrying capacity of the entire bay.

► We compare benthic infauna in mussel farms and reference sites at two spatial scales. ► There was no evidence of impacts on farms at the scale of 100 m. ► There was within-farm (10 m-scale) evidence of impacts within sampling sites. ► Disregarding effects at the 10 m-scale may mask effects in other studies. ► Current farming practices in baie de Gaspé seem to be sustainable.