Fish farms cause lethal and sublethal impacts on cold-water bamboo coral Isidella lofotensisUnderexplored Reefs

Bastien Taormina ^1,2, Inès Lukasik², Tina Kutti², Pål Næverlid Sævik², Helen Rastrick², Samuel Rastrick², Vivian Husa²

¹Institute of Marine Research, Norway - ²France Energies Marines, France

Atlantic salmon aquaculture using open-sea cages causes massive emissions of effluents in the environment, which alter the structure and functioning of surrounding benthic habitats. In this context, this study aims to evaluate in situ the impact of effluent coming from a new fish farm on an Isidella lofotensis bamboo coral garden in close proximity. Using video recordings taken along a gradient away from one fish farm over a three-year period, we evaluated visually the health evolution of the coral colonies. These observations have been put in relation with results of sedimentation models based on production data of the farm. Here we evidenced lethal and sublethal responses of I. lofotensis to effluents discharged by the fish farm. Particularly, bamboo corals around the fish farm exhibited significant overproduction of mucus during fish production. Furthermore, corals located underneath the farm and in close proximity showed substantial tissue necrosis and, in the most severe cases, complete tissue loss and mortality creating coral graveyards. Given the slow growth and long lifespan of I. lofotensis, the implementation of new conservation strategies is inevitable to mitigate the effects of salmon aquaculture on such ecosystems. This work offers the first in-situ sensitivity thresholds for cold-water corals, contributing to conservation and management efforts in areas impacted by aquaculture.