The contrasting differences in zooplankton community composition and abundance between aquaculture (mussel farm) and control sites in the Havre-aux-Maisons lagoon, QC

Relegated to the benthos, the blue mussel, Mytilus edulis, is confined to consuming resources available in the water above substrates. However, aquaculture manipulates the distribution of mussels and renders the resources of the water column available to mussels. With the identification of mussels as significant consumers of zooplankton, the presence of mussels in the water column suggests aquaculture could have an impact on the abundance and composition of zooplankton. The Havre-aux-Maisons Lagoon in the Magdalen Islands, QC has supported mussel aquaculture for over a quarter century. Water samples were obtained from farm and control sites in the lagoon in August 2010 to characterize the differences in zooplankton composition and abundance. Data indicates substantial differences between farm and reference sites. Multivariate analyses revealed significant differences in community composition between farm and reference sites (ANOSIM, p<0.05), whereas estimates of abundances indicated a significant reduction in zooplankton abundance in farm sites (t-test, p<0.05). While the mechanism for the observed differences remains unknown, the results suggest the presence of mussels in the water column can alter the structure and abundance of zooplankton communities.