Rocky Intertidal Community Structure on Santa Barbara Island and the Effects of Wave Surge on Vertical Zonation

Abstract

Rocky intertidal community structure was investigated at a site on the east shoreline of Santa Barbara Island, California by quarterly sampling over a 2-1/2 yr period. Zonational patterns of the macrobiota were determined by cluster analysis using percent cover data obtained from permanent quadrats established during the initial site visit. The resultant taxonomic and descriptive ecological data are discussed herein. Despite the fact that the study area was located on the leeward (sheltered) side of the island and did not receive direct wave shock, zonation of the biota was shifted dramatically upward. This elevated zonation is hypothesized to be the result of a persistent wave surge produced by refraction of the prevailing northwesterly swell around the northern and southern ends of the island. Vertical distributions of the dominant species of macrophytes and macroinvertebrates were compared between Santa Barbara Island and similar leeward sites on Santa Catalina Island (moderate surge impact) and San Clemente Island (low to negligible surge). For all species examined, vertical ranges were highest at Santa Barbara Island, intermediate at Santa Catalina Island and lowest at San Clemente Island.