Relationships Between Chemical Defense and Ecology in Benthic Ascidians

Abstract

Nearshore, benthic ascidians (35 spp.) were collected in Bermuda and notes were made on their habitat, microhabitat, susceptibility to epizoic recruitment, morphology and acidity. Some species (24) were later analyzed for V and Fe contents. Ten species had V concentrations of over 100 ppm d.w. (dry weight), 3 spp. had V concentrations of over 1000 ppm d.w. Fe contents were independent of V contents. Thirteen species had acidic (pH .ltoreq. 2) tunic fluids. Tunic fluid pH was not associated with V contents. V content was not significantly associated with habitat, microhabitat, susceptibility to epizoic recruitment or coloniality. Tunic acidity was significantly associated with habitat and lack of epibionts. No acidic species had macroscopic epibionts. Coloniality was significantly associated with lack of epibionts. These findings are discussed in reference to previous experimental work, which has shown that high V contents and acidity are involved in chemical defense in ascidians, and in reference to the role of chemical defenses in sessile, epibenthic, marine invertebrates.