Area-intensive bottom culture of blue mussels Mytilus edulis in a micro-tidal estuary

Abstract

Dredge fishery for blue mussels Mytilus edulis (L.) impacts the benthic ecosystem, and substitution by area-intensive bottom culture production may reduce adverse effects on the ecosystem. Two different field studies in 2007 and 2009 tested the productivity of bottom culture of blue mussels, and whether a shift from dredging of full-grown blue mussels to production of blue mussels in bottom culture could reduce the area of impacted sea bottom. In the first study, the macrostructure of a commercial bottom culture was analysed by side scan mapping, and the growth of blue mussels was recorded on a transect from the edge to the central part of the bottom culture. In the second study, we analysed the effect of seeding density (1.5 and 3.5 kg m −2 ) on mus- sel production. The measured production was used to model the affected area when producing blue mussels in bottom culture. The macrostructure of the culture bed formed during the trans- plantation of mussel seed was not changed 1 yr after transplantation, indicating that transplanta- tion supported the formation of a robust blue mussel bed. Shell growth showed no spatial variabil- ity from the edge to the central part of the commercial bottom culture, suggesting that growth was not reduced by density-dependent food limitation. The population production:biomass ratio (P/B) of the experimental bottom cultures was 1.0 and showed no significant effect of seeding density. Model simulations indicated that the impacted area was smaller when producing blue mussels in bottom culture than in a fishery of full-grown mussels if P/B was higher than 0.5.