Variability in prokaryotic and eukaryotic periphyton communities in marine recirculating integrated multi-trophic aquaculture systems

Integrated multi-trophic aquaculture (IMTA) systems produce multiple end-products, increasing revenue streams for the aquaculture industry. The inclusion of halophytes and periphyton have the added benefit of improving water quality by removing nitrogenous wastes. They can also be incorporated into aquafeeds and supplement oxygen, offsetting some of the greatest costs associated with recirculating aquaculture systems. Periphyton grows naturally on underwater substrates exposed to light and nutrients and in closed-system aquaculture may compete with halophytes for nitrogen compounds. Periphyton may also harbor bacteria associated with off-flavor production and potential fish pathogens. The goal of this study was to describe the eukaryotic and prokaryotic periphyton community structure under three recirculating IMTA system designs with or without halophytes. The taxonomic structure of both groups was predominately influenced by trial, indicating a larger influence of system design and/or season than of the presence of halophytes. When systems were fed continuously by fish effluent, periphyton communities were dominated by arthropods, fungi, and Pseudomonadota. Communities from systems seeded with sterile seawater and only initially with fish effluent were primarily composed of diatoms, roundworms, Bacteroidota, and Cyanobacteria. Periphyton communities contained taxa associated with off-flavor production, fish disease, and nitrogen cycling, but these functions were only predicted and not confirmed. This study indicates that periphyton community structure is influenced by various factors that may be adjusted to alter microbial composition in a manner that can increase nutrient content, nitrogen cycling, and oxygen supplementation.