Performance of blue mussel culture in nearshore and offshore environments

Abstract

Bivalve aquaculture in nearshore sites has expanded worldwide. Mussel farming productivity is commonly assumed to depend on survival and growth performance, which can be highly variable among spat stocks originating from different sites, even at a microgeographical scale. Using a traditional two-year production cycle, we monitored the productivity of neighbouring blue mussel (Mytilus edulis) spat stocks that had been cultivated in such contrasted environments that are shallow lagoons and open sea sites. We demonstrated that mussels collected in the nearshore, Bassin du Havre-Aubert (BHA) lagoon, exhibited the best survival rate (≥ 90%) in both nearshore and offshore sites, while other stocks experienced mortality as high as 60% under the same conditions. At spat recovery, the BHA spat stock showed higher gene expression levels for catalase and heat shock protein 70 (HSP70), which are involved in antioxidant defenses and the cellular stress response, respectively. Offshore conditions clearly enhanced overall growth performance independently of stock origin, as shown by the higher condition indexes, higher energy lipids (triacylglycerol), and generally higher glycogen content in mussels at the end of the production cycle. These observations of improved performance at the more favourable open-water conditions, particularly during summer, confirmed the importance of site-related environmental factors for productivity. The observed survival (+ 23%) and growth (+ 27%) trends support the hypothesis that offshore cultivation represents a valuable strategy for mussel aquaculture development. Considering current social, environmental, economic, and resource constraints, offshore mussel cultivation may be a viable alternative strategy for aquaculture development.