Keeping the water clean — Seaweed biofiltration outperforms traditional bacterial biofilms in recirculating aquaculture

In order to compare the efficacy of seaweeds and bacterial biofilm for removing nitrogenous wastes from recirculating marine aquaculture, Ulva lactuca L., Undaria pinnatifida Suringar, and a trickling biofilm filter were introduced to systems housing Haliotis iris Gmelin. Experiments were triplicated and run for 14 days. Although biofilm filtration maintained ammonium at low concentrations (around 0.10 mg l− 1), nitrate levels increased linearly over time, reaching 2.30 mg l− 1. Seaweeds maintained ammonium at concentrations that were consistently lower (around 0.03 mg l− 1) than those observed with biofilm filtration. Moreover, nitrates were undetectable and pH less variable, whilst valuable seaweed biomass, with increases up to 50%, was generated. Seaweed filtration thus has the potential to improve the efficiency and productivity of recirculating aquaculture, via enhanced culture conditions and the production of economically valuable biomass.