Partial recovery of infaunal communities during a fallow period at an open-ocean aquaculture

Abstract

Open-ocean or offshore aquaculture has attracted recent controversy for its potential environmental impacts and proposed expansion in the USA. Organic enrichment of benthic marine communities has been documented extensively under nearshore fish farms — primarily from fish feces and feed pellets — but relatively few studies have examined the effects of deeper, offshore operations. In this study, we investigate the effects of a 6 mo non-operational fallow period on ben- thic invertebrate communities surrounding a commercial offshore fish farm. Polychaete species diversity and community structure were analyzed at distant reference sites and farm-adjacent affected sites before, during and after the fallow period. The relative abundances of 3 polychaete indicator species for organic enrichment were also analyzed. During the fallow period, community structure at affected sites became more similar to communities at distant reference sites. Additionally, the sudden disappearance of enrichment indicator species at previously affected sites during the fallow period further suggests the beginnings of a recovery. However, species diversity did not increase significantly during the fallow period, indicating that the affected communities had not been fully restored to pre-culture or distant reference conditions. This study demonstrates the potential environmental benefits of scheduled fallow periods or crop rotations in offshore aquaculture.