USE OF AN EDIBLE RED SEAWEED TO IMPROVE EFFLUENT FROM SHRIMP FARMS

Nelson, S. G. 1 , Glenn, E. P. 1 , Moore, D. 1 , Walsh, T, 2 & Fitzsimmons, K. M. 11 Environmental Research Lab, University of Arizona, 2601 E. Airport Dr. Tucson, AZ 85706 USA; 2 SOEST Analytical Services Laboratory, University of Hawaii‐Manoa, Honolulu, HI 96822 USA An integrated shrimp and seaweed farm in Hawaii demonstrates the advantages of using algae to improve effluent quality from animal aquaculture operations. Gracilaria parvispora grown in the effluent channel of a commercial shrimp farm (Penaeus vannamei) absorbed significant quantities of nitrogenous and other waste compounds. Wild populations of the edible red seaweed were transferred into the effluent channel and grew at a Relative Growth Rate of 4.7% per day and increased it's nitrogen content from 1% to 3%. The weekly harvest of 100 kg from the effluent canal represented a removal of 3 kg of nitrogen from the effluent stream. An additional benefit was that seaweed could be fertilized in the ditch. Stocks of seaweed placed in the effluent ditch for five days would increase their nitrogen content from 1% to 3% and C:N ratio changed from 30:1 to 10:1. These algae would then be placed in cages in the ocean and would achieve growth rates of 9% per day compared to inorganically fertilized algae with RGR of 4.6% and unfertilized algae with RGR of 1.7%. Inorganic fertilizers that were formulated to mimic the concentrations in the effluent canal could not support the growth rate of the organic fertilization, implying that some micro‐nutrients or other factors were benefiting the algae growth.