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.

Marine epibiosis. I. Fouling and antifouling: some basic aspects

“…In some cases, fouled vicinity of the surface have repeatedly been postulated basibionts seem to attract grazers by exuded chemical to play a part in epibiont deterrence by plants (Baker & signals (Bronmark 1985). Orr 1986) and animals (Stoecker 1978(Stoecker , 1980. StoeckThe list of defense mechanisms established here is er's results on ascidian acid defense were questioned necessarily incomplete.…”

Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?

“…Feeding assays conducted with fish and crabs yielded a minimum deterrent concentration of vanadyl sulfate or sodium vanadate of f 100 Ag/g dry mass, which translated to a range of 1250-3333 Ag/g wet tissue mass (Stoecker, 1980a; and references cited therein). Stoecker (1980b) found 2 of 35 ascidian species from Bermuda contained wet tissue concentrations of vanadium within this range. Interestingly, one of these species, A. nigra, was also surveyed in the present study and was found to contain deterrent secondary metabolites in its zooid and gonad (Fig.…”

The Microenvironment and Photosynthetic Performance of Prochloron SP. in Symbiosis with Didemnid Ascidians

“…Host cells in the test contain highly acidic (pH<2-3) vacuoles of sulfuric acid, and can contain high concentrations of reduced organo-metallic complexes, especially with vanadium and iron (Carlisle 1968). A survey of Stoecker (1980) showed that didemnid ascidians from Bermuda especially accumulated iron and less vanadium, but if this is a general property of didemnids is to our knowledge unknown. Prochloron can also accumulate high levels of phenolic compounds (Barclay et al 1987).…”

“…Prochloron can also accumulate high levels of phenolic compounds (Barclay et al 1987). Acidity and high concentrations of reduced metal compounds and phenolics help protect ascidians against overgrowth and grazing (Stoecker 1980). The test is thus a light transparent living tissue providing a structured and protected environment with a large internal surface area for colonization by Prochloron.…”