A LONG TERM STUDY OF MICROBIAL AND ENVIRONMENTAL DYNAMICS IN AN INTENSELY IMPACTED AQUACULTURE ECOSYSTEM

Water quality, agriculture and human health are inextricably linked through aquatic microbial populations. One of the aquatic ecosystems most impacted by human influence is that of high-density aquaculture facilities, due to high fish biomass and intense feeding. Under these conditions pathogens and massive algal blooms, including those of toxin-producing strains, can cause fish stress and mortality.

To understand the dynamics of such intensely impacted ecosystems and evaluate the influence of anthropogenic and environmental effects on microbial populations, we have been following the microbiome of two fish ponds and an operating reservoir over more than two years at the Dor Aquaculture Research Unit. The concentrations of NO₃, NO₂, NH₄ and PO₄ in the ponds increase during winter months, whereas fish biomass typically peaks during the spring, suggesting that rainwater runoff from the surrounding agricultural fields is the major source of inorganic nutrients. Microbial population dynamics, assessed by 16S Illumina sequencing, indicate seasonal patterns characterized by high abundances of proteobacteria and bacteroidetes during autumn and winter and a shift towards cyanobacterial dominance during spring and summer. The cyanobacterial population includes Microcystis sp., potentially responsible for high concentrations of intracellular microcystins. No clear differences were found between the fish ponds and the operating reservoir which receives recirculated water, despite major differences in fish biomass. These results suggest that even in highly impacted ecosystems, natural seasonal rhythms dictate microbiome dynamics to a larger extent than human influence. Ongoing metagenomic analysis will shed light on the genetic underpinnings of these changes in community structure and, potentially, function.