Imposex in Thais clavigera (Neogastropoda) as an indicator of TBT (tributyltin) bioavailability in coastal waters of Hong Kong

Abstract

The degree of imposex (the imposition of male characteristics onto females) exhibited by females of Thais clavigera, collected during August 1996, was assessed using the Relative Penis Size Index (RPSI) and the Vas Deferens development sequence (VDS), to ascertain the extent of TBT (tributyltin) bioavailability in Hong Kong's coastal waters. All sites showed some degree of imposex development. The most affected areas were Victoria Harbour and Aberdeen where up to 92% of females were effectively sterilized by the development of a vas deferens, thereby, blocking the oviduct (VDS scores of 4-6 and RPSI of 32-41%). There is some evidence of this affecting the population structure of T. clavigera, i.e., a dominance of males in affected populations. A Tolo Harbour site, at Starfish Bay, remote from major shipping routes was the least affected having an 88% incidence of imposex (VDS scores of 0-2 and RPSI of <0.1%).