Effects of Heated Effluent on Hermatypic Corals at Kahe Point, Oahu

Abstract

The effect of thermal enrichment on hermatypic corals was investigated at Kahe Point, Oahu, Hawaii. The reef off the Kahe Power Plant was surveyed before and after an increase in thermal discharge that accompanied plant expansion. Abundances of dead and damaged corals correlated strongly with proximity to plant discharge and with levels of thermal enrichment. Nearly all corals in water 4° to 5° C above ambient were dead. In areas characterized by temperature increases from 2° to 4° C, the corals lost zooxanthellar pigment and suffered high mortality rates. Damage to the corals was most severe in late summer, and coincided with annual ambient temperature maxima. During the winter months the surviving corals slowly regained zooxanthellar pigment, but there was high mortality of corals during the recovery period. When generating capacity of the plant was increased from 270 to 360 megawatts, the area of dead and damaged corals increased from 0.38 hectare (0.94 acre) to 0.71 hectare (1.76 acre).