Journal of Chemical Ecology

, Volume 33, Issue 3, pp 643–654 | Cite as

The Role of Vanadium in the Chemical Defense of the Solitary Tunicate, Phallusia nigra

  • Shobu Odate
  • Joseph R. PawlikEmail author


Ascidians (sea squirts) may defend themselves from predators, biofouling competitors, and bacterial infection by producing secondary metabolites or sequestering acid, but many species also accumulate heavy metals, most notably vanadium. The defensive functions of heavy metals in ascidians remain unclear, and to this end, the solitary Caribbean tunicate, Phallusia nigra, was studied to localize vanadium in its tissues and to assess the defensive properties of vanadium-containing compounds. As determined by flame atomic absorption spectroscopy, the internal tissues and blood contained the highest vanadium concentrations (mean values of 2,280 and 1,886 ppm dry mass, respectively), followed by the tunic surface (871 ppm dry mass). Results of laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum, confirmed outcomes of past studies that demonstrated that vanadyl sulfate (VOSO4·6H2O) and sodium vanadate (Na3VO4) were unpalatable to fish, although these salts do not accurately reflect the chelation environment or oxidation state of vanadium in living tunicates. Fresh preparations of whole tunic, internal tissues, and blood were unpalatable to fish, but freezing and thawing of internal tissues and blood rendered them palatable. Crude organic extracts of whole tunic and internal tissues contained vanadium metabolites (225 and 750 ppm dry mass, respectively) and were palatable to T. bifasciatum; crude extracts also exhibited no antimicrobial effects against a panel of four marine bacteria known to be pathogens of marine invertebrates (Vibrio parahaemolyticus, Vibrio harveyi, Leucothrix mucor, and Deleya marina). Nonacidic vanadium (+3) complexes neither deterred predation nor inhibited microbial growth, whereas acidic aqua vanadium (+3 and +4) complexes were unpalatable to T. bifasciatum and exhibited antimicrobial activity. Difficulties in decoupling low pH from oxidation state and chelation environment of vanadium prevent definitive conclusions about the importance of some vanadium metabolites, but low pH appears to be the principal agent of chemical defense for P. nigra.


Tunicate Ascidian Predation Chemical defense Heavy metals pH Vanadium Acid 



This research was funded by grants from the NOAA/NURC Program (NOAA-NA96RU-0260), from the National Science Foundation Biological Oceanography Program (OCE-0095724, 0550468), and by a GlaxoWellcome Ocean and Human Health Fellowship. We thank Robert D. Hancock, Richard M. Dillaman, Richard D. Lancaster, Stephen A. Skrabal, and S. Bart Jones for advice and technical support.


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Copyright information

© Springer Science+Business Media, LLC 2007

Authors and Affiliations

  1. 1.Department of Biology and Marine Biology Center for Marine ScienceUniversity of North Carolina WilmingtonWilmingtonUSA

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