RESISTANCE OF A TUNICATE TO FOULING

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Abstract
Ascidia nigra is free of epibionts, although many other ascidians are susceptible to epizooic recruitment. Larvae of Pennaria tiarella and Ecteinascidia turbinata, 2 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. tiarella or E. turbinata is repelled by the toxic surface. The toxicity of A. nigra is probably due to the high V content (1022 ppm dry weight) of the surface deposit and to the release of free sulfuric acid from capsules in the test. Both the V-rich surface deposit and the acid-filled capsules are believed to be formed by degenerating vanadocytes in the test. V and sulfuric acid may also be involved in other allelochemical interactions such as defense against competitors, parasites and predators of ascidians.