Effects of Fish Farming on Benthic Bacterial Communities and Sediment Biogeochemistry: A Study on Microbiological Proxies for Environmental Assessment

Abstract

The fish farm sediments are characterized by high organic loading resulting from uneaten fish feed and feces, which accelerates anaerobic organic carbon (OC) oxidation such as sulfate reduction (SR). To accurately understand the environmental impact of aquaculture, it is important to identify the biogeochemical processes and microorganisms involved in the oxidation of OC in farm sediments. The purpose of this study is to elucidate shifts in major bacterial communities and biogeochemical processes across fish farming stages and to reveal suitable microbiological proxies for the environmental assessment. The rate of SR and the concentrations of its metabolites, acid volatile sulfide (AVS) and H2S, were significantly higher at the mid- and post-farming stages than at the early stage, indicating that the aquaculture effects persist even after harvest. Incomplete OC oxidizing sulfate-reducing bacteria (SRB), and gammaproteobacterial sulfur-oxidizing bacteria (SOB) were dominant during the early stage, whereas fermenting bacteria and complete OC oxidizing SRB, and epsilonproteobacterial SOB dominated during the mid- and post-stages. Especially, the Sulfurovum-like SOB correlated highly and positively with H2S, AVS suggesting that they could be relevant microbiological proxies to assess sulfidic conditions in farm sediment.