Review: Production of Gracilaria parvispora in two-phase polyculture systems in relation to nutrient requirements and uptake

Gracilaria parvispora Abbott is highly valued in Hawaiian seafood markets. Due to the over-harvesting of natural beds. G. parvispora is scarce on the open reef ; and harvesting is strictly regulated. On Molokai, Hawaii, a community-based operation was established to develop a sustainable, integrated culture system for this species. Previous research suggested that ammonium was the limiting factor for sufficient growth on the reef. Therefore, on Molokai, a polyculture system was developed using fish/shrimp ef- fluent to load thalli with nitrogen before placement in a low-nutrient lagoon for grow- out. The research described here demonstrates how small-scale, commercial culture of seaweed can be successfully integrated with the production of fish and shrimp. Two benefits of a two-phase polyculture system are: 1) a waste product from the first phase (i.e. ammonia nitrogen) becomes a resource for the second phase and 2) integrated sys- tems are financially more stable because of improved cash-flow and product diversifica- tion. A modest biomass of fish can support a substantial production of seaweed. The type of cage-based, polyculture system developed on Molokai could be applicable to other rural coastal areas.