Cultivation of Gracilaria parÕispora Rhodophyta in shrimp-farm effluent ditches and floating cages in Hawaii: a two-phase polyculture system

A culture system for the commercial production of the seaweed Gracilaria parÕispora using shrimp-farm effluents for fertilization and floating cage-culture for grow-out has been developed on Molokai, HI. This two-phase system produces high-quality products for direct human consumpŽ . tion. The mean relative growth rates RGRs of effluent-enriched thalli in the cage system ranged y1 Ž y1. from 8.8% to 10.4% day , a significant increase over the growth 4.6% day of thalli fertilized with inorganic fertilizer. Thalli were also grown directly in the effluent ditch, where mean growth rates of 4.7% day were obtained, less than in cage-culture. In the cage-culture system, thallus nitrogen content declined without fertilization. Effluent-enriched thalli grown in the cages steadily declined in nitrogen content, to about 1%, and their C:N ratios increased to between 20 and 30. However, when nitrogen-depleted thalli were transferred to the effluent ditch for enrichment, N content rapidly increased over 5 days to approximately 3%, with a C:N ratio near 10. Benefits of this two-phase polyculture system include enhanced growth of G. parÕispora and the use of effluent from commercial shrimp farms as a resource. q 2001 Elsevier Science B.V. All rights reserved.