Resilience of a rocky intertidal fish community in a physically unstable environment

Abstract

A 7-year census of intertidal fishes has been made by repeated defaunation of tide pools in the northern Gulf of California. The intertidal fish community showed long-term resilience and hence stability, under a rigorous, unstable physical environment. Although the majority of fishes have tropical affinities (76 %), warm temperate species (24 %) constitute 33 % of total numbers and 69 % of total biomass of the entire intertidal fish community. Short-term seasonal fluctuations in species diversity and population numbers of temperate fishes were in better synchrony with the annual light regime and sea temperature cycles than those of tropical species. A winterkill due to abnormally low sea temperatures in January, 1971, exerted faunal selection by killing several tropical fishes. Warm temperate species tolerated these low temperatures both experimentally and during the 1971 winterkill. Low sea temperatures were judged to be more limiting to diversity than high sea temperatures. The seasonal tidal pattern in the northern Gulf of California moderates summer heating but accentuates winter cooling thus favoring winterkills. We conclude that this intertidal fish community, dominated by r-selected species, is more physically controlled than biologically accommodated and the temperate species play an important rôle in regulating the stability of this fish assemblage.