Bioremediation using Gracilaria lemaneiformis to manage the nitrogen and phosphorous balance in an integrated multi-trophic aquaculture system in Yantian Bay, China

To reduce negative environmental impacts from human aquaculture activities, the red alga Gracilaria lemaneiformis was co-cultured with the fish Pseudosciaena crocea in an integrated multi-trophic aquaculture (IMTA) system for 35 d in Yantian Bay. The eutrophication index value decreased from 14.5 to 8.4 after seaweeds were co-cultured in cage farming areas, which indicated that the eutrophic water column in Yantian Bay could be mediated by IMTA. Total DIN and DIP of the tidal input and output were 9.23 kg, 0.19 kg and 11.08 kg, and 0.27 kg, respectively. Total 5.24 kg of dissolved N and 0.81 kg of dissolved P were released from IMTA system. These results indicate that G. lemaneiformis co-cultured in IMTA system could not completely remove all excess nutrients. In theory, at least 324.48 kg of seaweed seedlings would be required to balance excess nutrients generated from fish cages.