Abundance changes in Laminaria setchellii and Pterygophora californica (Laminariales, Phaeophyta) near the Diablo Canyon Power Plant

Abstract

Abundances of Laminaria setchellii and Pterygophora californica were determined three times per year for two years before startup of the Diablo Canyon Power Plant (DCPP) and thereafter for three years during which time the plant was in operation. The test site was situated at 3 m depth and was exposed almost continuously to heated effluent during plant operation. A control population was established about 60 m away from the test site and at an 8 m depth (i.e. lying below the heated plume). Abundances at both sites were relatively stable during the preoperational period. Abundances of Laminaria and Pterygophora declined, mortality increased, and recruitment ceased at the test site following plant operation and the discharge of heated effluent. In contrast, Laminaria abundance remained stable at the control site and a strong recruitment episode markedly increased Pterygophora densities during 1987, the final year of our study. Complete losses of Laminaria and Pterygophora were also observed in nearby shallow portions of Diablo Cove exposed to the thermal plume. Laminaria was more sensitive to heated effluent than Pterygophora. Adults of both species were more sensitive than juveniles.