Marine Flora and Fauna of Hong Kong and Southern China IV

Observations on the incidence of imposex in intertidal and subtidal Neogastropoda (Mollusca: Gastropoda) from Hong Kong

The Marine Flora and Fauna ofHong Kong and Southern China IV (ed. B. Morton). Proceedings of the Eighth International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 2-20 April 1995. Hong Kong: Hong Kong University Press, 1997. OBSERVATIONS ON THE INCIDENCE OF IMPOSEX IN INTERTIDAL AND SUBTIDAL NEOGASTROPODA (MOLLUSCA: GASTROPODA) FROM HONG KONG s.v. Proud and C.A. Richardson School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Gwynedd LL59 5EY, UK ABSTRACT Four species of neogastropods from the coastal waters of Hong Kong display varying degrees of imposex development, the superimposition of male sexual characteristics on the female. Two of the species examined, Thais clavigera and Thais luteostoma are common inhabitants of intertidal rocky shores whilst the other two, Nassarius siquijorensis and Bursa rana, occur subtidally. Male sexual characteristics, expressed as the presence of a penis, were observed in females of three of the species, i.e., T. clavigera, T. luteostoma and N. siquijorensis. This is the first reported incidence of imposex in Nassarius siquijorensis. Female Bursa rana showed no degree of imposex. The lengths and shapes of the penises of the four species examined were highly variable. In male Thais clavigera the penis was found to have an'S' shape which in some cases was highly coiled. The penis of Thais luteostoma was also'S' shaped, but tapered to a harpoon shaped tip. The longest penises were seen in male Nassarius siquijorensis where they were ribbon like structures, the tip ending in an oval aperture. Bursa rana, however, had a stout, straight, penis with a slightly upturned end. When present, the size of the female penis was much smaller than the males of that species. It is inferred that the male sexual characters displayed in the female neogastropods here studied is caused by the biocide tributyltin (TBT) used in antifouling paints and that, as a result of the different habitats occupied they could potentially be used as bioindicators of TBT pollution in a way similar to that already described for many neogastropods world-wide. 382 S.V. PROUD & C.A. RICHARDSON INTRODUCTION Imposex, the superimposition of male sexual characteristics on the female (Smith 1971), has been observed in around 80 species of neogastropods world-wide (Proud 1994). In many cases, strong evidence has been provided for the link between imposex and the presence in coastal waters of the biocide tributyltin (TBT) used in some antifouling paints, e.g., Ilyanassa obsoleta (Smith 1981), Nucella lapillus (Gibbs et al. 1988), Lepsiella scobina and L. albomarginata (Smith and McVeagh 1991). After exposure to TBT, female whelks develop male characteristics, usually expressed as the presence of a penis and vas deferens, in a dose dependent manner which is initiated in Nucella lapillus in the United Kingdom at concentrations as low as 0.5 ng Sn 1-1 (Bryan et al. 1986). Since its extent of development is correlated significantly with concentrations of tributyltin, imposex has been used as a bioindicator of TBT pollution in many countries (Gibbs et al. 1987; Ellis 1991). In ten species of neogastropod high concentrations of TBT render the female effectively sterile, e.g., Nucella lapillus (Bryan et al. 1986), Nucella lima (Short et al. 1989), and Thais haemastoma (Spence et al. 1990), having a severe effect on the population structure of these gastropods, most of which are either important predators or scavengers in intertidal and subtidal communities. Tributyltin antifouling paints have been used on the hulls of boats since the 1960s until concerns about the environmental damage to non-target marine life (Bryan and Gibbs 1991) led to restrictions on its use in some countries in the 1980s and early 1990s, e.g., UK; 1987 (Duff 1987), France; 1982 (Alzieu 1991), Western Australia; 1991 (Kohn and Almasi 1993). Most of the restrictions apply to the use of such paints on small pleasure craft which spend the majority of time moored in small bays and harbours where the restricted water exchange can lead to the build up of high concentrations of TBT leachates in the water. The territorial waters of Hong Kong are some of the busiest in the world and support craft of every size. Restrictions, banning the use of TBT based antifouling paints on boats less than 25 m in length, were brought into place in Hong Kong in 1992 (Ko et al. 1995). This brought Hong Kong into line with world-wide restrictions on the use of TBT paints. Tributyltin can, however, still be legally applied...