The decline of the gastropod nucella lapillus around south west england: Evidence for the effect of tributyltin from antifouling paints

Abstract

A survey of the gastropod Nucella lapillus around the south west peninsula of England has revealed that the incidence of imposex, the induction of male sex characters in the female, is widespread, that all populations are affected to some degree and that the phenomenon is most prevalent along the south (Channel) coast. Populations close to centres of boating and shipping activity show the highest degrees of imposex, especially those within the vicinities of the Helford, Fal, Salcombe and Dart estuaries and in Plymouth Sound and Tor Bay. Within Plymouth Sound the degree of imposex increased markedly between 1969 and 1985, coinciding with the introduction and increasing usage of antifouling paints containing tributyltin (TBT) compounds. The degree of imposex shows no correlation with the tissue burdens of arsenic, cadmium, copper, lead, silver and zinc but it increases with increasing concentrations of tin. Much of the tin found in body tissues is in a hexane-extractable form that includes both tributyltin and dibutyltin fractions. Transplantation of N. lapillus from a clean locality with little boating activity to a site close to a Plymouth marina caused a marked increase in the degree of imposex in the transplanted animals; analyses showed that of the hexane-extractable tin accumulated by the tissues of the transplants, 60-70% was in the tributyltin fraction. Laboratory experiments using tidal tanks show that imposex is readily induced by exposure to 0.02 μg/1 of tin leached from a TBT antifouling paint. It is thought that imposex could be initiated in N. lapillus by a concentration of tin, as tributyltin species, as low as 1 ng/1. Comparison of past and present observations of N. lapillus abundance show that many south west England populations are in decline; these populations are characterized by moderate to high degrees of imposex, often relatively fewer females, few juveniles and a general scarcity of laid egg capsules. A reduction in recruitment caused by a lowered reproductive capacity, rather than an increased mortality rate, appears to be responsible for the decline in N. lapillus numbers. Since the degree of imposex in N. lapillus is easily measured and may be related to the mean levels of tributyltin compounds to which the populations are exposed, the species has great potential as an indicator of the extent of TBT contamination. © 1986, Marine Biological Association of the United Kingdom. All rights reserved.