Diablo Canyon power plant site ecological study Annual Report July 1, 1976 - June 30, 1977 and Quarterly Report no. 16 April 1, 1977 - June 30, 1977

Abstract

More stations were surveyed during this report period than during any previous period. A total of 818 mandays was spent surveying 18 permanent and 67 random subtidal stations, 19 permanent and 50 random intertidal stations, and 64 sportfish catch-per-unit-of-effort stations, as well as conducting corollary laboratory work. In the subtidal areas, Laminaria dentigera and Pterygophora californica, both important subsurface kelp species, increased in their combined total numbers from the 1976 survey. However, Nereocystis luetkeana, the bull kelp, declined substantially in all study areas. Population trends of many of the dominant subtidal macro-invertebrates have varied depending on the species and on the type of method utilized. Regression analyses have been performed on selected species for numbers versus depth. Red algal abundance and diversity appear to have increased in both subtidal study areas. Of the three observation areas, sea otters were observed least frequently in Diablo Cove. However, there continues to be fresh evidence of otter foraging within Diablo Cove. Several seasons' data for intertidal algae and invertebrates have been summarized for one study area. While the algae biomass shows a fairly clear seasonality of abundance, the trends in numbers of the six invertebrate species considered are not as well defined. Because of high variability in the data, the sportfish catch-per-unit-of-effort and hook-and-line study was cancelled in December. Populations of intertidal red and black abalones, Haliotis rufescens and H. cracherodii, respectively, appear to have remained fairly stable during the 1976-77 period. Two other ancillary studies were also terminated during this period: interviews of commercial abalone and urchin fishermen, and observations of foam in Diablo Cove. (107pp.