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

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 of two to ten micromoles 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 including cattle pasturage and shrimp farming.

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 three to four 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.

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 that could be streamlined to increase the efficiency of post-harvest handling tasks.

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 are producing a revised Limu Growers Manual, which will be 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.