GROWTH OF NORI (Porphyra tenera) IN AN EXPERIMENTAL OTEC‐AQUACULTURE SYSTEM IN HAWAII

Abstract

ABSTRACTThe use of OTEC (Ocean Thermal Energy Conversion) effluents for aquaculture presents several benefits: reduced pumping costs, large‐scale temperature control, high water quality, and elevated levels of inorganic nutrients. Intensive culture of many temperate‐water organisms should be technically possible using these effluents. Nori (Porphyra tenera), a valuable edible red seaweed, is among the organisms being cultured experimentally in OTEC‐like water at the Natural Energy Laboratory of Hawaii, Keahole Point, Hawaii.Nori was cultured in 7 1‐m3 tank compartments with a mixture of deep (600 m) and surface water resulting in the following conditions: 15°C, 30 l/min flow rate, 26–29 μg‐at/l influent N concentration, 2‐2.5 μg‐at/l influent P concentration, 8‐hour photoperiod. The initial stocking density was 20 g wet weight (4.1 g dry wt) per compartment.After 39 days the nori averaged 4700±1525 g wet wt (622±121 g dry wt) per compartment. Maximum short‐term production rate was 27.9±7.7 g dry wt m‐2 day‐1. The nori extracted a maximum of 57% and 27% of the influent N and P, respectively, with 22–47% and 6–17% being more typical daytime values during the last two weeks. Little nutrient uptake occurred at night. Noon measurements revealed no significant excretion of organic C, N, or P; 24‐hour measurements were equivocal. Tissue N concentration (indicative of quality) was high relative to Japanese cultured nori during the first 3 weeks, but declined somewhat thereafter. P. tenera appears to have good potential for culture in OTEC effluents.