Local enhancement of epibenthic macrofauna by aquaculture activities

Abstract

Bivalve aquaculture can influence coastal marine ecosystems by increasing organic material deposition, which, in turn, can have multiple direct and indirect effects on the surrounding benthic community. We assessed the influence of blue mussel Mytilus edulis aquaculture on the epibenthic macrofauna at 4 sites in Prince Edward Island, eastern Canada. The abundance of macroinvertebrates and benthic fishes (>2 cm) was evaluated by visual counts using SCUBA within 4 mussel aquaculture facilities (‘farms’) and at locations at distances of 50, 100, 500 and 2000 m outside of them in June, August and November 2005. Benthic assemblages were dominated by seastars Asterias sp. (79%), rock crabs Cancer irroratus (8%), mud crabs Neopanope sayi (6%), moon snails Lunatia heros (2%), winter flounders Pleuronectes americanus (2%), American lobsters Homarus americanus (1%) and hermit crabs Pagarus sp. (1%). Although there was great variability among sites and sampling dates, mussel aquaculture had a clear effect on total abundance, which was generally greater within farms than at distances outside of them. These increases in abundance were mainly associated with increased numbers of seastars and rock crabs. Taxonomic richness and evenness differed among some mussel farms and distances outside of mussel farms, but there were no clear trends that suggested a negative influence of mussel aquaculture. Multivariate analyses indicated that communities within mussel farms differed from those at corresponding communities at distances outside of farms, but that the taxa that contributed to these differences varied among farms. Taxonomic assemblages for a specific farm and date were generally similar among distances outside of farms and increases in the abundance of epibenthic macrofauna appeared to be largely restricted to the immediate vicinity of mussel farms, i.e. <50 m. This increase in abundance probably reflected the attraction of mobile fauna due to increased food supply and possibly to the creation of a more heterogeneous habitat. These results suggest that large macroinvertebrates and benthic fishes, including ecologically and commercially important species, seem to respond positively to the presence of suspended mussel culture.