CHANGES IN PERIWINKLE (LITTORINA-LITTOREA) POPULATIONS FOLLOWING THE BAN ON TBT-BASED ANTIFOULINGS ON SMALL BOATS IN THE UNITED-KINGDOM

In 1987 the UK Government banned the use of tributyl tin (TBT)-based a ntifouling paints on small boats of less than 25 m. Following initial control measures taken in 1986, a program of research was started to m onitor concentrations of TBT residues in estuarine waters and sediment s and to observe faunistic changes in highly contaminated estuaries. A s part of this program, the size-frequency and abundance of Littorina littorea populations have been recorded in the estuaries of the rivers Crouch (Essex) and Hamble (Hampshire). Since the TBT ban, the concent ration of TBT residues in water and sediments has been steadily declin ing. In both L. littorea populations, the frequency of O-group individ uals has increased markedly, and there has been a simultaneous decreas e in TBT residues in L. littorea tissues. Furthermore, plankton survey s of the River Crouch show that the numbers of L. littorea eggs and ve liger larvae have progressively increased, suggesting that TBT may hav e impaired periwinkle reproduction and/or survival of the eggs and lar vae. Subsequent laboratory experiments have indeed shown that reduced egg production was the probable mechanism of action, but the imposer a ssociated with exposure to TBT in dogwhelks (Nucella lapillus) has not been seen.