Effects of recurrent sand deposition on rocky intertidal organisms: importance of substrate heterogeneity in a fluctuating environment

Abstract

This research represents a 3-yr (Sept., 1975-June, 1978) examination of a southern California [USA] rocky intertidal system influenced by variable sand deposition ranging from almost none to total seasonal inundation over different portions of the study area. An apparent subclimax association of opportunistic macrophyte (Chaetomorpha linum, Cladophora columbiana, Ulva lobata, Enteromorpha intestinalis) and highly-reproductive macroinvertebrates (Tetraclita rubescens, Chthamalus fissus/dalli, Phragmatopoma californica) dominate by rapidly repopulating those low-lying microhabitats routinely buried by sand. Refuge habitats on slightly elevated rock pinnacles (sand free) were dominated by long-lived mollusks such as Mytilus californianus, Haliotis cracherodii and Lottia gigantea. The lower limits of these biotically-competent taxa (sensu Vermeij, 1978) appear to be determined by the physical smothering action of sand, rather than by the kinds of biological factors documented for other rocky intertidal habitats. The stress-tolerant Anthopleura elegantissima dominates the upper intertidal macroinvertebrate cover because of reproductive, behavioral and physiological adaptations to the stresses of aerial exposure and sand burial. The dominant plant in lower intertidal pools is the biotically-competent Phyllospadix scouleri that tolerates sand because of its large size and its rhizomatous root system which traps and binds sediments. The most numerous of the mobile macroinvertebrates, Tegula funebralis, is able to migrate away from the winter sand inundation to refuge habitats. With few exceptions, sand-stressed habitats primarily serve as important refuges for 2 functional groups of species: stress-tolerant strategists and opportunistic strategists.