Relationships Between Chemical Defense and Ecology in Benthic Ascidians

Abstract

Thirty-five species of nearshore, benthic ascidians were collected in Bermuda and notes were made on their habitat, microhabitat, susceptibility to epizoic recruitment, morphology, and acidity. Twenty-four ascidian species were later analyzed for vanadium and iron contents. Ten species had vanadium concentrations of over 100 ppm d. W. (dry weight); three species had vanadium concentrations of over 1000 ppm d. W. Iron contents were independent of vanadium contents. Thirteen species had acidic (pH 5 2 ) tunic fluids. Tunic fluid pH was not associated with vanadium contents. Vanadium 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 vanadium contents and acidity are involved in chemical defense in ascidians, and in reference to the role of chemical defenses in sessile, epibenthic, marine invertebrates.