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

A culture system fur the commercial production of the seaweed Gracilaria pa rvispora using shrimp-farm effluents for fertilization and floating cage-cu lture for grow-out has been developed on Molokai, HI. This two-phase system produces high-quality products for direct human consumption. The mean rela tive growth rates (RGRs) of effluent-enriched thalli in the cage system ran ged from 8.8% to 10.4% day(-1). a significant increase over the growth (4.6 % day(-1)) of thalli fertilized with inorganic fertilizer. Thalli were also grown directly in the effluent ditch, where mean growth rates of 4.7% day( -1) were obtained, less than in cage-culture. In the cage-culture system, t hallus nitrogen content declined without fertilization. Effluent-enriched t halli 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 nitrog en-depleted thalli were transferred to the effluent ditch for enrichment, N content rapidly increased over 5 days to approximately 3%, with a C:N rati o near 10. Benefits of this two-phase polyculture system include enhanced g rowth of C, parvispora and the use of effluent from commercial shrimp farms as a resource. (C) 2001 Elsevier Science B.V. All rights reserved.