Effects of finfish aquaculture waste on the soft coral Gersemia rubiformis and sea anemone Aulactinia stella

Finfish aquaculture production in marine habitats can alter benthic communities through the sedimentation of fish feces and excess feed. The direct impacts of aquaculture wastes on habitat-forming species such as cold-water corals, and other benthic megafauna, are not well understood. Here, the soft coral Gersemia rubiformis and the sea anemone Aulactinia stella were exposed twice daily to low (5 g C m^-2 d^-1) or high (10 g C m^-2 d^-1) concentrations of salmon feed/feces, inorganic sediment (0 g C m^-2 d^-1), or no sedimentation over 28 days. Behaviour was recorded using timelapse videos and direct observations, and biochemical analyses were conducted post-trial. When exposed to wastes, G. rubiformis spent more time in an expanded state, which may assist with sediment and/or bacterial removal. Similarly, individuals of A. stella exposed to wastes spent more time with their tentacles extended and showed increased eversion of their pharynx, potentially as feeding mechanisms. Though no change in lipid composition was detected because of aquaculture waste exposure in either species after 28 days, a shift in the overall fatty acid composition was identified for G. rubiformis. As well, tracer fatty acids associated with salmon waste (18:2ω6 and 18:1ω9) were elevated in the biochemical profiles of both species following the low and high-waste treatments, suggesting selective assimilation of salmon feed. This study showed behavioural and biochemical effects in both G. rubiformis and A. stella over a short period of exposure to aquaculture wastes, raising important questions regarding the effects of long-term exposure to wastes.