ABSTRACT
A manipulative field experiment was designed to test the hypothesis that deposit feeding by an epibenthic holothurian, Parastichopus parvimensis (Clark 1913), influences the distribution and abundance of infaunal populations. The experimental design allowed separation of the effects of P. parvimensis from the other common bottom disturbers in the area, the labrid fishes Semicossyphus pulcher and Halichoeres semicinctus. Five “treatments” were replicated twice: 1) complete exclusion - no fish or sea cucumbers, 2) partial exclusion-fish allowed in, sea cucumbers excluded, 3) sea cucumber enclosure -1 sea cucumber/m2, 4) cage control - sea cucumbers and fish allowed access with as much caging material present as possible, and 5) uncaged control - sea cucumbers and fish allowed access with no caging material present. Tests showed no significant cage effects. Infauna were sampled at time 0, 1 year and 2 years, and sorted to major taxonomic group. Predator densities and feeding rates were monitored. The feeding rates of P. parvimensis varied throughout the year - the greatest amount of sediment being ingested during spring, with a significant decline during late summer through winter. Sea cucumber densities in shallow water (less than 13m) declined significantly during late summer and fall due to a downslope migration. The labrid fish had consistent feeding rates, but their densities also varied throughout the year. There was no detectable effect of holothurian deposit feeding on any of the infaunal groups. Neither normal, nor ten times normal, sea cucumber densities resulted in a significant change in either the absolute or relative abundances of the infaunal species groups. Release from labrid fish predation, however, did significantly increase the densities of the polychaete, Chaetopterus variopedatus, and the phoronid, Phoronopsis californica.
