THE AMERICAN OYSTER DRILL, UROSALPINX-CINEREA (GASTROPODA) - EVIDENCE OF DECLINE IN AN IMPOSEX-AFFECTED POPULATION (R-BLACKWATER, ESSEX)

The American oyster drill, Urosalpinx cinerea, introduced to UK waters around the turn of the century, flourished in the Essex oyster grounds until the 1970s. Recent observations, 1987-1990, made in Goldhanger Creek, River Blackwater, indicate that the population level has been reduced to the point of scarcity and that those individuals remaining are old. All females examined exhibited imposex. In most, this masculinizing syndrome was developed to an advanced state that involved oviducal malformation; copulation and egg capsule formation are thought to have been inhibited and hence such affected females were sterile. Other, probably very old, females appeared infertile because of senility. No viable spawn was observed during the four summers of 1987-1990. It is concluded that imposex resulting from tributyltin (TBT) pollution from marine antifouling paints has virtually, if not totally, eliminated all breeding activity in the population of U. cinerea in Goldhanger Creek. It remains to be determined whether populations in other Essex estuaries and along the Kent coast are similarly affected.