Deep-Water-Supported Mariculture

Deep-drawn seawater from an OTEC plant is cold, rich in nutrients, relatively free of pathogens, and available in large quantity. It is an excellent medium for growing phytoplankton and microalgae, which in turn support a variety of commercially valuable fish and shellfish. An OTEC plant can be part of a polyculture operation that combines the production of protein and energy. A seaweed used to wrap sushi (nori) was successfully grown at accelerated rates in experiments at the Natural Energy Laboratory of Hawaii (NELHA). Using phytoplankton and kelp, researchers at NELHA have grown salmon, trout, northern lobsters, oysters, giant clams, and abalone with good to exceptional results (Fast and Tanoue 1988).

The large, constant flow of water pumped from an OTEC plant will reduce disease and contamination in the ponds; marine life, therefore, can be grown in high densities. In addition, deep-drawn cold water can be mixed with warm surface water, allowing local communities to culture a broad variety of species. Such integration of operations would mitigate the large seawater pumping cost associated with mariculture and increase the revenue for the OTEC plant.

Mariculture facilities are best suited for land-based or near-shore plants rather than for offshore OTEC plants. At land-based or near-shore facilities, cold water can be pumped into tanks or lagoons where environmental conditions can be controlled more readily.