Recovery from imposex by a population of the dogwhelk, Nucella lapillus (Gastropoda: Caenogastropoda), on the southeastern coast of England since May 2004: a 52-month study.

Over a 52-month period beginning in May 2004 and concluding in August 2008, and coinciding with the period over which TBT was banned as a ship anti-foulant globally, a population of the dogwhelk, Nucella lapillus, was studied for changes in population size and structure, and reproduction. During the study period, the size of the population of N. lapillus on the Mewsbrook Groyne at Littlehampton on the southeastern coast of England grew from approximately 25 individuals to >500, i.e., a 20-fold increase. Similarly, population structure normalised to reveal a maximum age of up to approximately 3 years. The numbers of egg capsules produced by the N. lapillus population also grew over the study, again by a factor of 20, and the length of the breeding season increased from 7 months in 2004-2005 and 2005-2006 to 11 months in 2006-2007 and 2007-2008. Such changes were reflected in the incidence of imposex from Vas Deferens Index Stages 3 and 4 in 2003 to zero commencing in 2008 and continuing into 2009. Due to a lack of confirmatory chemical data, the changes in population size, structure and reproduction herein reported upon for N. lapillus cannot be correlated positively with changes in ambient TBT levels, but they can and are correlated with freedom from imposex. This is the first time such a dramatic recovery from imposex, following the banning of TBT, has been documented.