Early prediction of environmental deterioration in a coastal fish farming area using lactic acid bacteria as an indicator

We hypothesized that lactic acid bacteria (LAB) present in sediments at aquaculture sites can be employed as an indicator for the early prediction of deterioration, as the concentration of organic acids controls hydrogen sulfide production via sulfate-reducing bacteria. We selected two aquaculture sites with different acid volatile sulfide (AVS-S) values, St. OJ (average AVS-S = 0.24 mg S/g dry mud) and St. UM (average AVS-S = 1.16 mg S/g dry mud), which were less and critically deteriorated, respectively, and examined our hypothesis by performing a 3-year-long survey in Tanabe Bay, Wakayama Prefecture, Japan. In St. UM, the bacterial community showed positive correlations with AVS-S values and water contents. With AVS-S accumulation at the site, the abundances of LAB decreased below the detection limit, suggesting that LAB viable counts may be unsuitable for predicting early deterioration at sites with severe AVS-S accumulation. In St. OJ, the LAB viable counts, organic acid content, and AVS-S values increased after the beginning of sea bream aquaculture, and the bacterial community showed high correlations with the LAB counts, succinic and total organic acid concentrations, and the abundance of the class Bacilli. These on-site experiments indicated that LAB counts can be a reasonable indicator for evaluating deterioration in aquaculture sites.