Influence of Suspended Mussel Aquaculture and an Associated Invasive Ascidian on Benthic Macroinvertebrate Communities

Abstract

Many benthic macroinvertebrates are associated with cultured bivalves but are normally excluded from studies on the environmental effects of bivalve aquacultures. We evaluated the hypothesis that mussel aquaculture increases overall “benthic” macroinvertebrate productivity by considering both sediment- and mussel sock-associated macroinvertebrates. It was predicted that the presence of the invasive ascidian Styela clava would increase this effect by increasing the mussel sock’s biogenic structure. Macroinvertebrates in sediments and on mussel socks were sampled in eight bays on Prince Edward Island, Canada: three were invaded by Styela clava and there were five where it was absent. Infaunal macroinvertebrates associated with benthic sediments (sediment macroinvertebrates) within leases were less abundant relative to the control locations outside of leases and showed a trend towards decreased biomass and productivity. Abundance of mussel sock-associated macroinvertebrates was greater in bays with S. clava than in bays without it. When sediment and mussel sock macroinvertebrates were considered together as “benthic” communities within mussel leases and compared to sediment macroinvertebrate communities outside of leases, “benthic” macroinvertebrate abundance, biomass, and productivity were greater inside mussel leases than in areas outside of them. The presence of S. clava did not influence this trend. Although the ecological role of the macroinvertebrates associated with suspended mussels is likely not equivalent to those associated with benthic sediments, the presence of macroinvertebrates on suspended mussels, in some measure, offsets the impacts on the abundance, biomass, and productivity of macroinvertebrate communities at the farm-scale.