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

Substantial changes have occurred in assemblages of nearshore reef fis hes in the Southern California Eight during the past two decades. At t wo sites off Los Angeles, California, species richness of reef fishes fell 15-25%, and composition shifted from dominance by northern to sou thern species. Additionally, by 1993, 95% of the fish species had decl ined in abundance by an average of 69%. Concurrent declines of similar magnitude were observed for several trophic levels of the benthic eco system farther north at Santa Cruz Island where populations of surfper ches (Pisces: Embiotocidae), the standing stock of their crustacean pr ey, and the biomass of understory macroalgae all declined by similar t o 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 fe ll more than one order of magnitude over two decades and was correlate d among years with a broad indicator of Eight-wide productivity, the b iomass of macrozooplankton in the California Current. Lower productivi ty of the coastal marine ecosystem, associated with a climate regime s hift in 1976-1977, likely caused large, but unforeseen, impacts on pop ulation abundances and trophic structure in nearshore benthic communit ies.