Sustainable Food

      The seawater which is pumped ashore for an integrated land-based OTEC system has many potential secondary uses which have proven to be economically beneficial and can be incorporated into the plant design to offset and reduce the effective costs associated with OTEC energy. Aquaculture of both plants and animals is a particularly attractive by-product potentially included in an integrated OTEC system design.

OTEC Resource Advantage

     The cold, deep seawater required for OTEC has three principal advantages for aquacultural systems:

• Cold – The consistent low temperature of the deep water not only allows the culture of valuable cold water organisms in the tropics, it also provides (when mixed with the surface water or allowed to warm in the tropical sun) a means of precise, reliable and cost effective temperature control over the full temperature range from 6^oC to 25^oC.
  
  
• Nutrient-rich – The deep water is enriched with dissolved Nitrogen, Phosphorus, Carbon, and other chemicals which are essential to plant growth in the ocean.
  
  
• Pure – Since there is very little life at the depths from which it is pumped, the deep water has very few pathogens or viable plant cells. This permits the disease-free culture of sensitive organisms and the production of pure plant cultures without interference from competing species.

Mature Industry

     Mature and developing commercial aquaculture applications utilizing cold, deep seawater and surface water are currently being implemented at the Natural Energy Laboratory of Hawaii Authority (NELHA) in Hawaii to grow micro algae, macro algae, crustaceans such as shrimp and lobster, mollusks such as oysters and abalone, and finfish such as tilapia, flounder and salmon.

     The largest and most successful of the aquaculture applications at NELHA are growing micro algae for health food, pharmaceuticals, and fish and animal feed products. Micro algae are commercially attractive because they grow quickly in the strong tropical sun. Cyanotech, Inc. grows Spirulina, a health food supplement. The tremendous advantage of micro algae over other aquaculture organisms is their rapid growth cycle. If the Spirulina cultures experienced catastrophic failure (which has never happened to date at NELHA), they can be back in production in 2 to 3 weeks. The corresponding time period for salmon, lobster, abalone, etc. is 3 to 6 years.

     Kona Cold Lobster, Ltd., another NELHA tenant, grows Maine Lobster (Homarus americanus) in Hawaii by using the cold water to optimize the lobster’s aquatic environment. They keep the water at the optimum 20^oC year round, so that the animals grow to 500 gm size in about 3 years. In nature they hibernate in the winter, so the animals require seven years to reach this size!

     Other marketable aquaculture products have also been, and are currently being developed for commercial applications appropriate for integration into an OTEC system for a tropical island community. Other available products include, but are not limited to, oysters (both as food stock and pearl culturing), abalone, clams, shrimp (as food source and brood stock), giant clams (Tridacna), Dungeness Crab, salmon, tilapia and tropical reef fish for aquariums (see accompanying table).

Natural Energy Laboratory of Hawaii Authority

Tenants: September 1998

(Courtesy: Natural Energy Laboratory of Hawaii Authority)

     OTEC aquaculture not only holds the benefit of self-sustaining food resources for tropical island communities and its tourism related industry, but also holds the potential of creating a readily available, commercially attractive, exportable industry to further the diversity of the tropical island economy as well as providing necessary job opportunities to local island residents.