| The structure of a rocky intertidal fish assemblage was examined on the rocky headlands and cobble beaches of the Strait of Juan de Fuca, Washington. Thirty-two species of fish were collected in nearly 600 collections. Only 16 species regularly inhabited the intertidal (primary and secondary residents); the remaining 16 species (transients) comprised less than 1% of all individuals collected. All of the resident fishes occurred in tidepools, but only six species occurred beneath rocks at low tide. The density and standing crop of fish was significantly higher in tidepools and beneath rocks on the rocky headlands than on the cobble beaches.;The assemblage of intertidal fish was shown to be highly resilient. The fishes were quick to recolonize empty habitats, and there were no extinctions or invasions during the study. Space did not appear to be a limiting resource.;The assemblage of fishes partitioned the intertidal by microhabitat and, to a lesser extent, by food resources. The most widely distributed species, Oligocottus maculosus, Gobiesox maeandricus, and Anoplarchus purpurescens, all primary residents, utilized the greatest range of microhabitat and food resources, and formed the "core" of the assemblage. The remaining primary residents were more specialized in their use of microhabitats and, in some species, their use of food resources. The secondary residents were generally more specialized than the primary residents in microhabitat and food utilization.;Microhabitat and food specialists were added to the assemblage of core species along a gradient of increasing spatial heterogeneity, substrate relief, and temporal predictability of low tide refugia. The addition of specialists restricted the vertical distribution and range of microhabitats utilized by the core species, presumably by competition for food.;The Cottidae dominated the assemblage with eight species and 60% of all individuals collected. They were followed by the Stichaeidae with four species and 28% of all individuals collected. Nine of the 16 resident species (82% of all individuals collected) were primary residents that spend, with the exception of their larval existence, all of their lives in the intertidal. The remaining seven species (17% of all individuals collected) were secondary residents that inhabit the intertidal: (1) only as juveniles, (2) seasonally migrate into the intertidal for reproduction, or (3) facultatively inhabit the intertidal, the upper limit of their vertical distribution, as juveniles and/or adults. |
