CHANGES IN AN ASSEMBLAGE OF TEMPERATE REEF FISHES ASSOCIATED WITH A CLIMATE SHIFT

Abstract

Substantial changes have occurred in assemblages of nearshore reef fishes in the Southern California Bight during the past two decades. At two sites off Los Angeles, California, species richness of reef fishes fell 15-25%, and composition shifted from dom- inance by northern to southern species. Additionally, by 1993, 95% of the fish species had declined in abundance by an average of 69%. Concurrent declines of similar magnitude were observed for several trophic levels of the benthic ecosystem farther north at Santa Cruz Island where populations of surfperches (Pisces: Embiotocidae), the standing stock of their crustacean prey, and the biomass of understory macroalgae all declined by -80%. Abundances of fishes fell because declining recruitment of age-0 fish was insufficient to compensate for losses of older age classes. Annual levels of recruitment of age-0 fishes at all reefs examined fell more than one order of magnitude over two decades and was correlated among years with a broad indicator of Bight-wide productivity, the biomass of macrozooplankton in the California Current. Lower productivity of the coastal marine ecosystem, associated with a climate regime shift in 1976-1977, likely caused large, but unforeseen, impacts on population abundances and trophic structure in nearshore benthic communities.