Distribution and productivity of fish and macroinvertebrates in mussel aquaculture sites in the Magdalen islands (Quebec, Canada)

Aquaculture structures may function in a manner analogous to artificial reefs, in that they provide a complex three-dimensional habitat for marine organisms and/or modify the surrounding environment. Further, aquaculture structures may increase the productivity of fish and macroinvertebrates similarly to natural complex habitats, such as seagrass beds. This research tested the general hypothesis that suspended bivalve culture increases the abundance and productivity of fish and macroinvertebrates. The study was done at two mussel farms in the Magdalen Islands, eastern Canada. Fish and macroinvertebrates were sampled in different areas within farms sites and in adjacent natural vegetated and unvegetated habitats. The instantaneous growth rates of winter flounder (Pseudopleuronectes americanus), sand shrimp (Crangon septemspinosa) and the rock crab (Cancer irroratus) were estimated using physiological indicators (RNA/DNA ratios). The results demonstrated that mussel sites are not equivalent to natural structurally complex seagrass beds with respect to fish and macroinvertebrate assemblages. Several species were abundant in mussel farms, including winter flounder and rock crab. This work, however, provided little evidence to suggest that there was greater productivity of these fish and macroinvertebrates at mussel farms, as growth rates were usually equivalent in different habitats. This study, to our knowledge, is the first attempt to determine changes in productivity brought about by aquaculture. As future development of mussel aquaculture increases in many regions around the world, the methods presented here will provide baseline information on the abundance and productivity of fish and macroinvertebrates associated with aquaculture sites. (C) 2008 Published by Elsevier B.V.