PERIPHYTON COMMUNITY DYNAMICS WITHIN AN INTEGRATED MULTI-TROPHIC AQUACULTURE SYSTEM

The removal of waste nutrients in aquaculture effluents remains a limitation to expansion of the industry. Fish retain 20-30% of the nitrogen in feed; t he remainder is released into the water. Ammonia is the main catabolic product, but effluents also carry nitrate and nitrite.  Integrated multi-trophic aquaculture (IMTA) systems incorporate plants to absorb these nutrients, improving water quality and producing a valuable by-product. Plants preferentially uptake ammonia  whereas periphyton, the aquatic biota that develops as a natural film on submerged substrate with nutrients and light, is thought to  deplete  both ammonia and nitrate.  The present study investigated the biological potential of periphyton-based biofilters for nutrient removal in fish production systems.

Nutrient assimilation trials were conducted in a marine IMTA system containing red drum Sciaenops ocellatus and  sea  vegetables Sesuvium portulacastrum, where wastewater from fish culture flowed into plant aquaponic raceways through a series of integrated production tanks. Eukaryotic and prokaryotic periphyton communities were characterized using sequencing technologies in two different system configurations: periphyton only (P ) or periphyton and  sea vegetables (P+SV). Response parameters (water chemistry, water quality, plant growth,  and periphyton growth and biomass) were measured throughout a 5 week trial.

Prokaryotic communities were similar between P and P+SV systems (Table 1) .  The family Saprospiraceae , a group thought to break down fish wastes  into nutrients used by  aquaponics plants, was dominant in all communities. The cyanobacterium Leptolyngbya , which thrives in high organic content waters, was also abundant. Eukaryotic communities were different between P and P+SV systems (Table 2). Periphyton grew faster in P systems, perhaps due to greater abundances of the carotenoid-producing yeast Sporobolomyces in P treatments .  P systems had greater abundances of the nutrient-rich diatom Amphora.  No differences in terms of  nutrient removal between treatments. O ptimization of the IMTA system is currently underway.