Sustainable Culture of the Edible Red Seaweed, Gracilaria parvispora, in Traditional Hawaiian Fishponds

Final Report for SW97-025

Project Type: Research and Education
Funds awarded in 1997: $95,201.00
Projected End Date: 12/31/1999
Matching Non-Federal Funds: $14,202.00
Region: Western
State: Arizona
Principal Investigator:
Edward P. Glenn
Univ. of AZ, Dept. of Soil, Water & Env. Science
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Project Information

Project Objectives:

1. Establish methods to break dormancy of sporelings.
2. Establish methods for sustainable cage cultures.
3. Design and test seaweed cleaning machine.
4. Disseminate information through workshops, growers' network, revised how-to manual and technical publications.


Research results and discussion:

1. Establish methods to break dormancy of sporelings

Experiments were conducted with sporelings as well as older plants to determine the factors limiting growth on the reef. Plants were placed out at six locations on the reef, and biomass production was compared to water quality factors (water motion, temperature, salinity, turbidity, nitrate, ammonia, phosphorous and silicon levels) at each site. The experiment was repeated three times, in spring, summer and winter. The results showed that ammonia levels in the range 2-10 uM controlled the growth of Gracilaria on this reef (r2 = 0.83); no other water quality factors were significantly correlated with growth. Elevated ammonia levels at specific sites were associated with land-based activities that enriched the reef levels of ammonia. These land use practices included cattle pasturage and shrimp farming.


E. Glenn, D. Moore, M. Akutagawa, A. Himler, T. Walsh and S. Nelson. 1999. Correlation between Gracilaria parvispora (Rhodophyta) biomass production and water quality factors on a tropical reef in Hawaii. Aquaculture 178:323-331.

2. Establish methods for sustainable cage culture.

A sustainable production system was developed in which Gracilaria was harvested from the reef or from shrimp effluent ditches, then transferred to cages for additional growout. Plants removed from effluent ditches were found to be highly enriched in nitrogen content, so when transferred to cages they were able to utilize this nitrogen for growth. After 3-4 weeks in cages, the plants doubled or tripled in weight and were much cleaner than when taken from the reef or ditches. This material was cleaned and sold in Honolulu. For a complete description of the production system see:

E. Glenn, D. Moore, J. Brown, R. Tanner, K. Fitzsimmons, M. Akutagawa and S. Napolean. 1998. A sustainable culture system for Gracilaria parvispora (Rhodophyta) using sporelings, reef growout and floating cages in Hawaii. Aquaculture 165:221-232.

3. Design and test seaweed cleaning machine.

Funding to build a cleaning machine was removed from the budget by USDA. Rather than fabricate a machine, we conducted time and motion studies on the hand cleaning process and identified procedures which could be streamlined to increase the efficiency of post harvest handling tasks.

4. Disseminate information through workshops, growers' network, revised how-to manual and technical publications

Numerous workshops and public demonstrations were held throughout the project, and participation in ogo growing increased to over 30 families as a result. Ke Kua'aina Hanauna Hou and the University of Arizona have produced a revised Limu Growers Manual, which is self published by Ke Kua'aina and distributed to participants in the limu project on Molokai. The manual contains: introduction; life cycle diagrams; ogo cultivation procedures; explanation of the 'Ohana Growers Network and Limu Buyback Program; and a section on marketing fresh and value added ogo products.

Research conclusions:

This project provides an important means by which local coastal residents can derive an economic benefit from the public domain reef on Molokai. This reef has been subjected to siltation and eutrophication from non-traditional land use practices, which include clearing native vegetation on the slopes to improve grazing (which produces erosion) and to residential development along the coast, which increases nutrient levels through leakage from septic systems. Growing ogo on the reef aids the environment by (1) giving local residents an economic stake in maintaining a productive reef ecosystem and (2) introducing a crop that can help absorb excess nutrients entering the reef. At present, sales of Molokai ogo are approximately $100,000 per year, providing supplemental income to some 30 families along a 16-mile length of coastline. There is great potential for expansion, as the wholesale buyers pay a $2.50 per kg premium for Molokai ogo and have markets in Japan and the mainland USA that would absorb unlimited additional production.

Participation Summary

Research Outcomes

No research outcomes

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Finding have been disseminated through journal articles prepared by the University of Arizona, and by workshops, outreach and extension carried out by UA, Ke Kua'aina, and Glen Tevis, University of Hawaii Agricultural Extension Agent on Molokai. In addition, Ke Kua'aina has self published and distributed the Limu Growers Manual. This project will continue under separate funding, and UA and Ke Kua'aina will continue to dissiminate results and increase the community participation in ogo growing on Molokai.

Education and Outreach Outcomes

Recommendations for education and outreach:

Areas needing additional study

The high dependence of ogo productivity on ammonia opens up several avenues for increased production and greater environmental stewardship. For example, we are now initiating a project to combine ogo production with shrimp and fish culture (already practiced on Molokai). The ogo will help scrub nutrients from effluent water before it is discharged onto the reef. We believe this type of project would also be successful in other Pacific Island locations, including Guam and the former Pacific Trust Territories for which USDA still has responsibility.

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.