AN EVALUATION OF THE POTENTIAL OF GASTROPOD IMPOSEX AS A BIOINDICATOR OF TRIBUTYLTIN POLLUTION IN PORT-PHILLIP BAY, VICTORIA

Imposex, the imposition of male sexual characteristics on female marine snails, was used as an indicator of past and present exposure to tributyltin (TBT) in the abundant muricid whelk Thais orbita (Gmelin). Wild populations of Thais orbita were surveyed for frequency and intensity of imposex throughout Port Phillip Bay and at two sites on the adjacent oceanic coast. Imposex indices correlated strongly with proximity to marinas or harbours. Average TBT body burdens for each population were mostly below 10 ng g-1 Sn (as TBT, wet wt) and failed to correlate with imposex indices. Even the highest body burdens were indicative of low contemporary ambient TBT levels. Thais orbita females from a population with negligible levels of imposex were transplanted to two sites where the highest imposex indices were found. Transplants failed to develop a significantly higher frequency or intensity of imposex than controls after 11 weeks. These results confirm that, as with many other gastropod species, imposex in T. orbita is irreversible, and may be found in populations where TBT contamination is no longer present. Nevertheless. controlled transplantation of T. orbita shows promise as a routine bioindicator of contemporary TBT contamination in southern Australia. Imposex in other gastropod species in Port Phillip Bay is described and discussed.