Development of a Sustainable Polyculture Seaweeds and Fish on Molokai

Final Report for SW01-026

Project Type: Research and Education
Funds awarded in 2001: $95,200.00
Projected End Date: 12/31/2004
Matching Non-Federal Funds: $18,743.93
Region: Western
State: Arizona
Principal Investigator:
Stephen Nelson
University of Arizona Environmental Research Lab
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Project Information


A two-phase polyculture system was designed for producing seaweeds and marine fish on the island of Molokai. The system is operated by a nonprofit 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, resulting in increased production and decreased labor. A series of workshops were held on Molokai to demonstrate the technology and provide training for local aquaculture workers.

Project Objectives:
  1. 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. Increase farm revenues through product diversification and increased production.
    4. 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

The proposed project was designed to contribute to the development of an integrated aquaculture system on Molokai, as part of long-standing and on-going efforts to revitalize rural communities and conserve traditions of land use in Hawaii. The project was based on previous successes resulting from cooperative work by the Environmental Research Laboratory of the University of Arizona and Ke Kua'aina Hanauna Hau (KKHH), a nonprofit, community development organization based on Molokai.
A sustainable, community-based, aquaculture system for the production of edible seaweed has been developed on the island of Molokai in Hawaii. The system was described in detail by (Glenn et al., 1998) and is focused on the production of an economically and culturally valued natural resource, the seaweed Gracilaria parvispora. The project is part of a Molokai community effort to revitalize the island's rural coastal economy through the introduction of diversified aquaculture enterprises (Wyban, 1993a,b) and incorporates the major strategies of ecological design: conservation, regeneration, and stewardship (Van der Ryn and Cowan, 1996).
The seaweed, known locally as long ogo, was traditionally harvested from near-shore waters throughout the Hawaiian islands and has become an important commodity of present day commerce. Although once abundant at many sites within the local coral reefs, the standing crops of G. parvispora have, as a result of over harvesting, been severely depleted in recent years. The Molokai aquaculture operation was established to replenish the stocks of this seaweed in nature, to make this traditional food available again to the local markets, and to provide supplementary income for many individuals within the community. As a result of the productive relationship between researchers and producers involved in the project it has been successful in providing local markets with increasing supplies of fresh seaweed. Sales of of ogo by KKHH in 1999 totaled 23,476 pounds with a wholesale market value of approximately $75,000.
In the Molokai aquaculture system, spore-laden substrata are produced in a small-scale seaweed nursery operated by KKHH. These are provided to individuals to use in establishing out-plantings, or patches, of seaweed that can be harvested periodically and sold to the cooperative as stock to be grown in cages where they are fertilized weekly (Glenn et al., 1998; Nelson and Glenn, 2000). The seaweed is subsequently harvested, and the final product, a fresh or pickled vegetable, is marketed locally and also exported to Honolulu and Japan. Recent research efforts have been directed toward improving the various phases of the production cycle for this system (Glenn et al., 1998; 1999 Nelson et al., 2001).
The success of the out-plantings has been highly variable and appears to depend primarily on the availability of dissolved nitrogen (Glenn et al., 1999). Though the ocean waters of the reefs of Hawaii are generally low in nutrients, activities on the coastline can result in localized areas of elevated nutrients. Among such sources of nutrients from land-based activities on the coast of Molokai are marine shrimp farms, which discharge nutrient-rich water through drainage ditches into the reef environment. We noticed that the drainage ditches quickly develop characteristic ecosystems dominated by macroalgae, particularly Gracilaria parvispora. Our previous research has shown how production in these self-organized ditch ecosystems can be integrated into the existing seaweed aquaculture system on Molokai, thus using the waste from one aquaculture operation as a resource for another.
The environmental benefits of integrating the production of aquatic plants with the production of fish or shrimp to recapture nutrients are well known (e.g., Buschmann et al., 1994; Neori et al., 1996; Shpigel and Neori, 1996; Chopin and Yarish, 1998; Mathias et al., 1998; Truell et al., 1997). Most of the research on integrated plant-animal aquaculture systems have used intensive, land-based culture methods (Buschmann, et al., 1994; Neori et al., 1996; Shpigel and Neori, 1996). Growing multiple cash crops such as shrimp, fish, bivalves, and seaweeds in extensive systems is common in Asian aquaculture systems (Chen, 1990), but they have neither been widely adopted in western aquaculture nor subjected to the same kind of rigorous analysis as the intensive systems noted above. In some intensive systems, a green algae (Ulva) has been successfully established, whereas Gracilaria performed poorly (Neori et al., 1996).
Our previous research has shown that, in contrast, G. parvispora appears to be well suited to culture in pond effluent in extensive production systems; it becomes established in the effluent ditches and persists as a dominant species even without direct management. Recent work by producers on Molokai has demonstrated that this species can also be effectively produced in tanks with effluent from fish (tilapia) culture. KKHH has purchased supplies of ogo produced in this manner. Preliminary observations indicate that approximately 500 pounds of ogo can be produced from an initial stocking of 80 pounds, within one month. Data are needed on fish and ogo densities that will result in optimal yields in these land-based nursery systems.
Coupling the production of seaweeds directly with the culture of marine fish or shrimp minimizes or eliminates environmental impacts of coastal aquaculture facilities. The discharge of ammonia-rich effluent from fish and shrimp farms can result in eutrophication of the receiving water bodies, and, thus, aquaculture can be a major source of coastal pollution (Costa-Pierce, 1996; Hopkins et al., 1995a,b; Iwama, 1991; Wu, 1995). Eutrophication is especially disruptive on oligotrophic tropical reefs such as the one on Molokai, which can develop nuisance algae blooms in response to fertilization. Hence, any agricultural or aquaculture system based on the tropical and sub-tropical coasts near such reefs should contain environmental safeguards. Species of Gracilaria are particularly attractive candidates for recovering nutrients from shrimp or fish farm effluents because they are capable of the rapid uptake and storage of nitrogen (Ryther et al. 1981). These physiological characteristics allow thalli of Gracilaria species to exploit pulses of elevated dissolved nitrogen and to store the excess to support growth during times when nutrient levels are lower (D=Elia and DeBoer, 1978; Hanisak, 1987).
In previous work, we demonstrated the benefit of the use of high-nutrient waters in a sequential polyculture system linking seaweed production with shrimp farms (Nelson et al., 2001). We found that enrichment of the thalli in shrimp-farm effluent prior to their transfer to the cage grow-out systems resulted in much higher rates of growth. Within the effluent ditches, the thalli were provided the opportunity for luxury uptake of nitrogen; which was later used to support higher growth rates when they were transferred to the cage-culture system. The mean number of days in the system for thalli that are fertilized, but not effluent-enriched, has been reported to be 44 days (Glenn et al., 1998). Use of thalli that had been grown in the shrimp effluent was calculated to reduce the mean time in culture from four weeks to approximately three weeks, considerably shortening the production cycle. The effluent from shrimp farms proved to be useful as a resource for the cage culture of seaweeds, allowing increased production and shortened production cycles. Therefore, we proposed a two-stage polyculture system in which Gracilaria harvested from ditches is cleaned and multiplied in the ocean, through cage culture, prior to sale (Nelson et al., 2001).
Others have also reported increased growth of farmed seaweeds in response to nutrient enrichment from coastal aquaculture operations. For example, Troell et al. (1997) reported that, in the coastal waters of Chile, the relative growth rates of Gracilaria chilensis thalli within 10 m of an array of salmon cages were 40% higher than those more distant, 150 m from the cages.
Literature Cited:
Buschmann, A.H., Mora, O.A., Gomez, P., Bottger, M, Buitana, S., Retamales, C., Vergara, P.A., Guiterrez, A. 1994. Gracilaria tank cultivation in Chile: use of land-based salmon culture effluents. Aquaculture Engineering 13, 283-300.
Chen, L. 1990. Aquaculture in Taiwan. Blackwell Scientific Publications, Ltd., Oxford.
Chopin, T., Yarish, C. 1998. Nutrients or not nutrients? World Aquaculture 29, 31-33; 60-61.
Costa-Pierce, B. 1996. Environmental impacts of nutrients from aquaculture: towards the evolution of sustainable aquaculture systems. In: D. Baird, M. Beveridge, L. Kelly and J. Muir (eds.), Aquaculture and Water Resource Management, Blackwell Science, Oxford, pp. 81-113.
D=Elia, C.F., DeBoer, J.A. 1978. Nutritional studies of two red algae: II. Kinetics of ammonium and nitrate uptake. J. Phycol. 14, 226-272
Glenn, E.P., Moore, D.,. Akutagawa, M., Himler, A., Walsh, T, Nelson, S.G. 1999. Correlation between Gracilaria parvispora (Rhodophyta) biomass production and water quality factors on a tropical reef in Hawaii. Aquaculture 178, 323-331.
Glenn, E.P., Moore, D., Brown, J.J., Tanner, R., Fitzsimmons, K., Akutigawa, M, Napolean, S. 1998. A sustainable culture system for Gracilaria parvispora (Rhodophyta) using sporelings, reef growout, and floating cages in Hawaii. Aquaculture 165, 221-232.
Hanisak, D. 1987. Cultivation of Gracilaria and other macroalgae in Florida for energy production. In: K. Bird and P. Benson (eds.), Seaweed Cultivation for Renewable Resources, Elsevier: Amersterdam, pp. 191-218.
Hopkins, S., Sandifer, P., Browdy C. 1995a. A review of water management regimes which abate the environmental impacts of shrimp farming. In: C. Browdy and S. Hopkins (eds.), Swimming Through Troubled Water, Proceedings of the Special Session on Shrimp Farming, Aquaculture >95, World Aquaculture Society, Baton Rouge, Louisiana, pp. 157-166.
Hopkins, J., Sandifer, P., Devoe, M., Holland, A,, Browdy, C., Stokes, A. 1995b. Environmental impact of shrimp farming with special reference to the situation in the continental United States. Estuaries 18, 25-42.
Iwama, G. 1991. Interactions between aquaculture and the environment. Critical Reviews in Environmental Control 21, 177-216.
Mathias, J., Charles, A., Baotong, H. (eds.). 1998. Integrated fish farming. CRC Press, Boca Raton, Florida, 420 pp.
Nelson, S.G. and E.P. Glenn. 2000. Spore and sporeling production in the development of aquaculture systems for species of Gracilaria and related seaweeds. p. 1-21 in M. Fingerman and R. Nagabhushanam (eds.), Recent Advances in Marine Biotechnology Volume 4: Aquaculture, Part A Seaweeds and Invertebrates. Science Publishers, Inc. USA.
Nelson, S.G., E.P. Glenn, J. Conn, D. Moore, T. Walsh, M. Akutagawa. 2001. Cultivation of Gracilaria parvispora (Rhodophyta) in shrimp-farm effluent and floating cages in Hawaii: a two-phase polyculture system. Aquaculture 193: 239-248.
Neori, A., Krom, M., Ellner, S., Boyd, C., Popper, D., Rabinovich, R., Davidson, P., Divr, O. Zuber, D., Ucko, M., Angel, D., Gordin, H.. 1996. Seaweed biofilters as regulators of water quality in integrated fish-seaweed culture units. Aquaculture 141, 183-199.
Shpigel, M., Neori, A. 1996. The integrated culture of seaweed, abalone, fish and clams in modular intensive land-based systems: I. Proportions of size and projected revenues. Aquacultural Engineering 15, 313-326.
Rhyther, J.A., Corwin, N., DeBusk, T.A., Williams, L.D. 1981. Nitrogen uptake and storage by the red alga Gracilaria tikvahiae. Aquaculture 26, 107-115.
Thompson, T.L., Glenn, E. 1994. Plaster standards to measure water motion. Limnology and Oceanography 39, 1768-1779.
Truell, M., Halling, C., Nilsson, A., Buschmann, A.H., Kautsky, N., Kautsky, L.. 1997. Integrated marine cultivation of Gracilaria chilensis (Gracilariales, Rhodophyta) and salmon cages for reduced environmental impact and increased economic output. Aquaculture 156, 45-61.
Van der Ryn, S., Cowan, S. 1996. Ecological design. Island Press, Washington, D.C.
Wu, R. 1995. The environmental impact of marine fish culture: towards a sustainable future. Marine Pollution Bulletin 31, 159-166.
Wyban, C. 1993a. Proceedings of the Governor=s Molokai fishpond Restoration Workshop. Aquaculture Development Program, State of Hawaii, Honolulu, 129 pp.
Wyban, C. 1993b. Report of the Governor's Task Force on Molokai Fishpond Restoration. Department of Business, Economic Development and Tourism, State of Hawaii, Honolulu, 37 pp.


Click linked name(s) to expand/collapse or show everyone's info
  • Edward Glenn
  • Colette Machada


Materials and methods:

The method of producing G. parvispora (ogo) in fish tanks is modified from practices developed at a commercial aquaculture farm on Molokai that primarily focuses on production of shrimp and fish. The production tanks were set up adjacent to the lagoon where ogo is being commercially produced via cage culture. This producer is concerned primarily with ogo production, with fish as a secondary crop.
The experimental production units were 5-ft diameter fiberglass tanks supplied with flowing seawater from the adjacent lagoon.
Ogo production
Initially the project focused on identifying the influence of combinations of environmental factors: water exchange rate, fertilization rate, and water motion, on the specific growth rates of individual thalli of G. parvispora in tank cultures. A series of replicate, 14-day, experiments were conducted. In these trials without fish, fertilization was supplied in pulses with a fertilizer mix that is currently being used in cage culture of ogo. We conducted a series of growth trials with tagged thalli. The independent variable was the specific growth rate of an individual thallus, each tagged with a mylar tag attached by a loop of monofiliament. The dependent variables were water motion and nitrogen level. Water motion was altered by airstones in the tanks and it was estimated from weight loss of plaster of paris blocks (Thompson and Glenn, 1994). Nitrogen level was varied by the effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii, and the addition of fish or chemical fertilizer.
We concentrated on production of local fishes in order to eliminate the protential problems involving introduced species and to contribute to the ongoing efforts to maintain island traditions with regard to fish culture. We used grey mullet (Mugil cephalus) and milkfish (Channos channos). Juveniles for stocking were obtained from the hatchery of the Oceanic Institute, other growers, or collected from the wild. Fish were stocked and raised in batches with stocking occurring once or twice per year. Rearing practices, such as feeding rate and frequencies, were in accordance with the fish-culture training provided to the KKHH staff by the Oceanic Institute on Oahu.

With the data derived from the growth trials and literature estimates of fish excretion rates, we estimated stocking density ratios of fish and seaweed to provide reasonable expectations of supporting ogo production. These trials were conducted in 12 18-ft diameter tanks with polyethelene liners. The data were analyzed with analysis of variance.
Partial nitrogen budgets for the fish and ogo production trials were determined. Nitrogen in water samples was determined at the SOEST analytical laboratory of the University of Hawaii. The nitrogen content in biomass samples was determined through analysis with a C:N anlalyzer at the Soil and Water Analytical Laboratory of the University of Arizona.

Research results and discussion:

Nutrient enrichment
The project team 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 based on seaweed growth rates, seaweed nitrogen uptake, ammonia production by milkfish, and algae nitrogen content. Nutrient-poor thalli (1% nitrogen) are placed for enrichment for one week into tanks used for the milkfish culture. After the enrichment period, the thalli contained 4-5% nitrogen and grew at high rates (more than 10% a day) when placed in grow-out cages in the nutrient-poor coastal waters of Molokai. For details see Ryder et al. (2004b).
Two-phase polyculture system
The edible red seaweed, Gracilaria parvispora Abbott, was pulse-fertilized in tanks using fish-culture water or chemical fertilizer, then cultured in floating cages in a low-nutrient, ocean lagoon in Molokai, Hawaii. Small, daily additions of ammonium sulfate and ammonium diphosphate were the only additions needed to stimulate growth. Fish-culture water was as effective as chemical fertilizer in supporting growth. Thalli fertilized for 7 days in tanks contained 2.5-5% nitrogen in tissues by the end of the treatment period; upon transfer to low-nutrient water, nitrogen content decreased to 1% as the nitrogen was mobilized to support growth. Thalli grew rapidly over the first 14 days after transfer from fertilizer tanks to the ocean, achieving relative growth rates of 8-12% per day and producing yields of 57 g dry wt. m-2 d-1. However, by 21 days after transfer growth ceased due to depletion of stored nutrients. The optimal stocking densities are in the range of 2-4 kg m-3 based on growth rates. Nearly all net growth occurred in the cages rather than in the fertilizer tanks, which serve only to introduce nitrogen into the thalli. The yields obtained here are 4 times higher than achieved previously with this species and are comparable to high-yielding, intensive tank cultures. For details see Nagler et al. (2003).
Water motion
A cage culture system was developed for the red alga Gracilaria parvispora Abbott on Molokai, Hawaii; but yields have shown marked variation even among cages with identical stocking rates and fertilization treatments. Water motion, which can be affected by location of the cages in grow-out area and with respect to placement of other cages, was hypothesized to be a factor contributing to the variation in yield. To examine this, the growth rates of thalli and the development of sporelings in relation to water motion were determined in replicated trials both in tanks and in small-scale field experiments. Water motion had a substantial effect on both thallus growth rate and spore development. In the tank cultures of thalli, water velocities ranged between 0.0 and 13.7 cm s-1, which produced relative growth rates (RGRs) ranging from 2.8 to 8.9% day-1. In the lagoon, water velocities ranged between 3.6 to 11.6 cm s-1. Relative growth rates of the thalli in the lagoon trials were 0.02 to 10.3% day-1.
Sporeling density, a measure of spore development, was also significantly affected by water motion. In the tank trials, water motion ranged from near 0 to 6.50 cm s-1, and sporeling densities ranged from 1.4 cm s-2 at lower water motion levels to 11.6 sporelings cm s-2 at higher levels. Similar results were obtained in lagoon trials with sporeling densities ranging from 0.2 to 6.7 cm s-2. On the other hand, length of sporelings was not significantly correlated with water motion. In previous trials, we have been able to achieve high sporeling densities but elongation of sporelings has been inhibited. In the present trials, we were able to break the apparent sporeling dormancy by incubating the sporelings in tanks enriched in nutrients supplied by fish cultures. Consideration of these effects of water motion is important in designing culture systems for species of Gracilaria and other marine algae. The finding with respect to spore culture suggests that nutrients play a key role in regulating the early development of sporelings. For details see Ryder et al. (2004b).
Training Workshops
Training workshops were presented by Ke Kua’aina Hanauna Hau regarding the culture of seaweeds and fish. The workshops consisted of a combination of classroom lectures by aquaculture scientists from the University of Arizona and hands-on field experience at on-going commercial aquaculture sites on Molokai. The workshops were each attended by 25 trainees.
Technical material, both in lectures and in the field training, was presented by three researchers from the University of Arizona’s Environmental Research Laboratory (ERL). These were:
1) Edward P. Glenn, Phd., Professor of Soils, Water, and Environmental Science (SWES)
2) Stephen G. Nelson, Phd., Senior Research Scientist and adjunct Professor, ERL
3) Ms. Casey McKeon, MS, Phd candidate in the Department of Soil, Water, and Environmental Science.
The lectures and demonstrations were supplemented by information presented in handouts and in a: “Aquaculture and Fisheries Management, Renewable Natural Resources Student Reference,” College of Agriculture, the University of Arizona, Tucson, Arizona, 81 p.
The first portion of the training sessions focused on the biology and culture of seaweeds, while the latter portion focused on fish biology and culture. Topics in the first portion included: the marine environment and its influence on seaweeds, algal communities, algal physiology and life history, and seaweed cultivation. In the second portion of the training sessions topics included: an overview of world aquaculture production, fish growth and physiology, fish handling, water quality issues in fish culture, and disease prevention and diagnosis. Practical experience included: seeding coral chips and gravel with algal spores, anesthetizing fish, construction of cages, measuring water motion, determination of dissolved oxygen and ammonia, fertilization of seaweeds in culture, and the use of diagnostic software for fish health.
After completing the training sessions, each trainee provided a written evaluation of each of the instructional components and exercises. The trainees were encouraged to provide input into how the workshops could be improved and what topics that they would like to see addressed in future workshops.

Research conclusions:

The protocols developed for a two-phase polyculture system have been successfully employed in the commercial production of seaweeds and fish on Molokai. The importance of nitrogen and water motion in seaweed cultivation on Molokai has been demonstrated. The adopted protocols have resulted in increased production and decreased labor requirements.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

The project resulted in three scientific publications and one MS thesis:

Nagler P., E. Glenn, S. Nelson, and S. Napolean. 2003. Effects of fertilization treatment and stocking density on the growth and production of the economic seaweed Gracilaria parvispora (Rhodophyta) in cage culture at Molokai, Hawaii. Aquaculture 219: 379-391.

Ryder, E. 2003. Effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii. MS Thesis, Dept. Soil, Water, and Environmental Science, University of Arizona.

Ryder, E., S. Nelson, C. Mckeon, E. Glenn, K. Fitzsimmons, and S. Napolean. 2004a. Effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii. Aquaculture 238: 207-219.

Ryder, E., S. Nelson, E. Glenn, P. Nagler, S. Napolean, and K. Fitzsimmons. 2004b. Review: Production of Gracilaria parvispora in two-phase polyculture systems in relation to nutrient requirements and uptake. Bull. Fish. Res. Agen. Supplement 1: 71-76.

In addition, results of the project were presented at meetings of the World Aquaculture Society in San Diego, Brazil, and Honolulu. Results of the project were also presented at seminars at the University of Arizona, and the University of Guam. Workshops with 20-25 participants were held on Molokai each year. Four graduate students at the University of Arizona received training through involvement with the project.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

More study is needed to diversify the market and to evaluate other economic seaweeds for production in conjunction with fish and shrimp farms.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.