Development of a Sustainable Polyculture Seaweeds and Fish on Molokai

Development of a Sustainable Polyculture Seaweeds and Fish on Molokai

Summary

A two-phase polyculture system was designed for producing seaweeds and marine fish on the island of Molokai. The system is operated by a local, non-profit organization involved in aiding native Hawaiians. Research focused on developing protocols for the use of nutrients in effluent from fish culture to support the small-scale commercial production of the red alga Gracilaria parvispora, known locally as “ogo”. The fertilization protocols developed have been adopted by the grower and have resulted in increased production and decreased labor. Also, a series of aquaculture workshops were held on Molokai to demonstrate this production technology and to provide training to local aquaculture workers.

Objectives/Performance Targets

1. Determine optimal stocking densities for fish and seaweeds in an integrated, tank-based production system for supplying fresh seafood to local markets.
2. Determine nitrogen budgets for these systems for use in farm management to reduce reliance on artificial fertilizers, increase seaweed production, and prevent eutrophication of the local nearshore water.
3. To increase farm revenues through product diversification and increased production.
4. To encourage, through direct demonstration and the dissemination of technical information, the development of integrated aquaculture systems appropriate for small-scale coastal farms on Molokai and other Hawaiian islands

We have established a protocol for waste nutrients from fish culture to support the commercial production of the seaweed Gracilaria parvispora in Hawaii. The protocol was developed with data on growth rates of seaweed, nitrogen uptake of seaweed, ammonia production by milkfish, and nitrogen content of the algae. Nutrient poor (1% nitrogen) thalli are placed for one week for enrichment into to tanks used for the culture of milkfish. After this enrichment period, the thalli contained 4 to 5% nitrogen and grew at high rates (over 10% per day) when placed grow-out cages in the nutrient-poor coastal waters of Molokai. The data generated through our research have been presented at two international conferences and have resulted, thus far, in two scientific publications. In the coming year efforts will focus on refining the nitrogen budgets of the fish and investigating other factors that effect the growth of seaweeds in cage culture.
In addition, training workshops were presented at the facilities of Ke Kua’aina Hanauna Hou on Molokai regarding the culture of seaweeds and fish. The workshops consisted of a combination of lectures by scientists from the University of Arizona and hands-on field experience at on-going commercial aquaculture sites on Molokai. The workshop series was attended by 25 trainees. Additional workshops will be held during the second year of the project.

Impacts and Contributions/Outcomes

Our research has involved the development of protocols for a two-phase polyculture system that has been successfully employed in the commercial production of seaweeds and fish on Molokai. The seaweed being produced is the red alga Gracilaria parvispora and the fish being raised in the system are milkfish Chanos chanos. The protocols that we developed have been adopted by the grower and have resulted in increased yields and lower labor requirements. Production of enriched seaweeds in cages ranged from 39-57 g dry mass m-2 day-1 in a 21-day grow-out phase. The details of the system have been published (Nagler et al, in press; Ryder et al., in press), and these papers were presented at scientific meetings in San Diego and Japan.
Local workshops to demonstrate and explain the technical details of the polyculture system were well received and attended by approximately 25 people on Molokai. The information has also generated interest by other growers and has stimulated the development of cooperative arrangements among several small-scale fish, shrimp, and seaweed producers on Molokai. In addition, three graduate students from the University of Arizona have received training in aquaculture as a result of their participation in the project.

Literature cited
Nagler, P.L., E.P. Glenn, S.G. Nelson, and S. Napolean. 2002. Effects of fertilization treatment and stocking density on the growth and yield of the economic seaweed Gracilaria parvispora (Rhodophyta) in cage culture at Moloka’i, Hawaii. Aquaculture (in press)

Ryder, E., S. Nelson, E. Glenn, P. Nagler, S. Napolean, and K. Fitzsimmons. In press. Production of Gracilaria parvispora in two-phase polyculture systems in relation to nutrient requirements and uptake. Proceedings of International Aquaculture Symposium, Japan.

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