Bioremediation of Saline Aquaculture Effluent Using an Extractive Assemblage of Perna perna, Paracentrotus lividus, and Ulva lactuca: A Preliminary Trial in a Laboratory-Scale IMTA Prototype

Aquaculture systems that rely on external feed inputs can generate effluents enriched with suspended solids, particulate organic matter, and dissolved nutrients, which can impair water quality if not properly managed. Integrated multitrophic aquaculture (IMTA) is based on combining a production compartment with extractive compartments that have complementary ecological functions, capable of retaining, transforming, and/or assimilating a fraction of the particulate and dissolved effluents. A saline IMTA prototype was designed around three functional compartments: a rearing unit generating effluents, a particulate and benthic extractive compartment housing the mussel Perna perna and the purple sea urchin Paracentrotus lividus, and an algal compartment with Ulva lactuca, prior to recirculating the water back to the aquaculture unit. The experiment lasted 60 days, during which suspended solids, ammonium, nitrates, nitrites, and phosphates were monitored, as well as the survival and growth of the introduced organisms. At the end of the trial, spatial concentration gradients were observed between the rearing unit and the algal compartment. Suspended solids dropped from 18 to 1 mg L⁻¹, ammonium from 6.12 to 0.62 mg L⁻¹, nitrates from 18.45 to 1.10 mg L⁻¹, nitrites from 0.50 to 0.04 mg L⁻¹, and phosphates from 5.12 to 0.15 mg L⁻¹, representing apparent relative decreases of 94.4%, 89.9%, 94.0%, 92.0%, and 97.1%. Biological responses indicate short-term maintenance of the extractive organisms, with survival rates of 93% for P. perna and 90% for P. lividus, while U. lactuca exhibited an average daily growth rate of 2.3%. These results suggest that the tested extractive assemblage was associated with a marked reduction in particulate concentrations and dissolved nutrients under controlled laboratory conditions. This study should nevertheless be considered preliminary proof of concept. Further replicated trials incorporating rigorous controls, optimized extractive-species stocking densities, continuous water-quality monitoring, and nitrogen and phosphorus mass balances are needed before any operational upscaling can be considered.