Microbial communities in coastal sediments impacted by fish farming

A prominent ecosystem impact of fish farming is the increased influx of organic matter that stimulates anaerobic mineralization and sulfide production in underlying sediments. In severe cases, sulfide can diffuse into the overlying water leading to euxinia. We propose that the sustainable management of aquacultural activities calls for a better understanding of natural sulfide detoxification by microbially mediated sulfide oxidation. Electrogenic cable bacteria, a recently discovered bacterium in coastal sediments, conducts a highly efficient form of sulfide oxidation. Cable bacteria perform electrogenic sulfide oxidation, supported by long distance electron transport over centimeters, which is known to play a crucial role in the prevention of euxinia. This study provides insight into 1) the geochemistry and microbiology of impacted sediments, and 2) the recovery process of fish farm sediments during fallowing, through the induction of a diverse community of sulfur-oxidizers, enhanced by cable bacteria growth. The potential for sulfide removal by cable bacteria is evident from our findings, however their geochemical dominance is hindered during the production period possibly due to sediment disturbances (particle sedimentation from cages). Alternatively, we suggest that cable bacteria, and the associated microbial community, may thrive during fallowing, mitigating the impact of fish farming on the seabed and accelerating the recovery of ecosystem functions.