Absorption efficiency of mussels Mytilus edulis and Mytilus galloprovincialis cultured under Integrated Multi-Trophic Aquaculture conditions in the Bay of Fundy (Canada) and Ría Ares-Betanzos (Spain)

11 páginas, 6 figuras, 5 tablasIntegrated Multi-Trophic Aquaculture (IMTA) is a recycling concept in which waste nutrient discharges from high trophic levels become an additional energetic input for extractive organisms such as bivalves. The aim of this study was to measure the seston levels and absorption efficiency of mussels reared in the proximity of fish net-pens. The absorption efficiency of mussels Mytilus galloprovincialis and Mytilus edulis cultured at sites adjacent to red sea bream (Pagellus bogaraveo) and salmon (Salmo salar) cages was assessed on site, using natural seston diets and compared with mussels reared distant from the cages in the Ría de Ares-Betanzos (Galicia, N.W. Spain) and the Bay of Fundy (S.W. New Brunswick, Canada), respectively. Total particulate matter and the organic and the inorganic fractions of the seston were measured simultaneously. Seston parameters were generally similar at the mussel sites close to the fish cages and at the reference sites. However, significantly higher particulate inorganic matter coupled with lower food quality (seston organic content) observed at the sites close to the fish cages suggested occasional sediment resuspension events in the Ría de Ares-Betanzos and the Bay of Fundy. Owing to the reduced food quality, 20% lower absorption efficiency was measured for mussels in the proximity to the cages during the resuspension events. No significant differences in absorption efficiency were detected between the fish cages and the reference sites outside the resuspension events. Consequently, differences in absorption efficiency were attributed to natural variations in seston organic content, and absorption increased with increasing food quality. The results showed no evidence of increased organic content of the seston resulting from proximity to the fish-farm. It was concluded that proximity of cultured mussels to the fish cages did not result in an enhancement of the absorption efficiency.This study was sponsored by the project Ecological Sustainability of Suspended Mussel Aquaculture (ESSMA) awarded by the Programa Nacional de Internacionalización I+D, Subprograma ‘Fomento de la Cooperación Científica Internacional (FCCI)’ by the Spanish Ministry of Science and Innovation (ACI2008-0780). J. Irisarri is grateful for financial support from ‘Junta para la Ampliación de Estudios’ JAE-Predoc CSIC-FSE scholarship and this study forms part of her Ph.D. Thesis.Peer reviewe