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Marine aquaculture or mariculture is farming of saltwater organisms either at sea (near shore) or on land. Tropical or temperate mariculture at sea is central to an environmental controversy and may pose several threats to marine and coastal biodiversity due to wide-scale destruction and degradation of natural habitats, concentration of antibiotics in fish feces and unconsumed food, accidental releases of genetically altered or hybridized fish into the wild that compete against and can crowd out smaller or less voracious native fish, and transmission of diseases to wild stocks. However, aquaculture applications utilizing cold, deep ocean water (DOW) in improved recirculating tanks, ponds or raceways on land are currently being implemented at the Natural Energy Laboratory of Hawaii Authority (NELHA) in Hawaii and have led to a drastic reduction in such pollution threats.

DOW aquaculture takes advantage of the three properties of deep ocean water:

  • Cold – The consistent low temperature of the deep water not only allows the culture of valuable cold-water organisms, but also provides (when mixed with the warm surface seawater 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°C to 24.5°C, thereby producing environments acceptable to many temperate and tropical species of marine life.

  • Nutrient-rich – The deep water has elevated levels of dissolved inorganic nitrates, phosphates and silicates 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 is free of pathogens (bacteria and viruses) and has very few viable plant cells. This permits the disease-free culture of sensitive organisms and the production of pure plant cultures without interference from competing species.

Currently, the main types of marine organisms being produced through mariculture at
NELHA include microalgae and macroalgae, mollusks such as oysters (both as food stock and pearl culturing), clams and abalone, crustaceans such as shrimp (both as food source and brood stock) and Maine lobster, finfish such as tilapia, flounder and salmon, and tropical reef fish for aquariums.

The high nutrient levels of the deep seawater produce more rapid growth and higher protein content in microalgae and macroalgae grown in appropriate mixtures of the cold deep seawater and warm surface seawater. Cyanotech Corporation, NELHA's largest tenant, is successfully growing


Cultivation of microalgae in Cyanotech's 600-foot long raceways equipped with paddle wheels at NELHA
Spirulina , a microalga, which is very high in protein and beta-carotene. This product is sold world-wide as a health food supplement. In addition, Cyanotech produces the pigment astaxanthin (a red pigment extracted from algae which is sold to growers of salmon and shrimp to impart the natural pink color, thus providing a natural alternative to the artificial pigments that are currently utilized by most growers around the world) and phycobiliproteins (fluorescent pigments used in immunological diagnostics).
Royal Dutch Shell plc and HR Biopetroleum have formed a joint venture company, called Cellana, to construct a pilot facility in Hawaii to grow marine microalgae in open-air ponds of seawater and produce vegetable oil for conversion into biofuel. The site, leased from NELHA, is near existing commercial algae enterprises, primarily serving the pharmaceutical and nutrition industries.

Royal Hawaiian Sea Farms, Inc. has been developing culture technology for a variety of commercially useful macroalgae at NELHA for several years. They produce and market limu, or “edible sea vegetables”, which form a very important part of the human diet in
Hawaii, Japan, China and other Asian countries, providing proteins and vitamins. They have also developed a large production and marketing capability for several varieties of Gracilaria from which agars are extracted and used in foods. In addition to sea vegetables, they produce saltwater tilapia. Kona Cold Lobster, Ltd., another unique NELHA tenant, mixes cold deep seawater with some warm surface seawater to yield a 21°C (70°F) bath that allows Maine lobsters to thrive. This mixture accelerates growth so that the crustaceans mature in three years instead of the seven years it normally takes lobsters in the wild to grow to a

Cultivation of “sea vegetables” at NELHA
market weight of 500 gm (1 lb). In this way the animals are exposed to only summertime temperatures, avoiding the three-month hibernation each year that stalls growth in Maine’s waters.

Also, mixtures of surface and deep seawater have been used to grow salmon at NELHA. A Japanese seafood company, Uwajima Fisheries, Inc. has a commercial facility at NELHA that produces hirame, a delectable flounder used in sushi. In addition to hirame, Uwajima Fisheries produces brood stock shrimp that are grown to help restock shrimperies in the world that have been wiped out by shrimp viruses.

 

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