RESISTANCE OF A TUNICATE TO FOULING

¹ Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794

Ascidia nigra is free of epibionts, although many other ascidians are susceptible to epizooic recruitment. Larvae of Pennaria tiarella and Ecteinascidia turbinata, two epibenthic species found in the same habitats in Bermuda as A. nigra, were used in laboratory experiments which (demonstrated that the surface of A. nigra's test is toxic to settling larvae. There was no evidence that P. tiarclla or E. turbinata is repelled by the toxic surface. The toxicity of A. nigra is probably due to the high vanadium content of the surface deposit and to the release of free sulfuric acid from capsules in the test. Both the vanadium-rich surface deposit and the acid-filled capsules are believed to be formed by degenerating vanadocytes in the test. Vanadocytes may also be involved in defense against competitors, parasites, and predators of ascidians.