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SEPG 2239 - Date Awarded 2003
Trends in Mollusc populations in Estuaries damaged by TBT Pollution
Bill Langston, Gary Burt and Belinda Chesman
Abstract
Molluscs are the most sensitive of organisms to the effects of tributyltin (TBT). The Southampton area harbours commercial shipping, ferries and warships together with thousands of small craft. Not surprisingly, it became one of the most heavily TBT-polluted areas of the UK. Infaunal bivalve populations have been surveyed at intervals at sites in Southampton Water and its estuaries since 1978 to assess the impact of TBT (in terms of bioavailability and abundance) and the effectiveness of TBT legislation. Nine sites were re-surveyed in 2004. Data for Scrobicularia plana reveal diverse trends in relation to patterns of TBT usage and distribution. Populations at most sites declined during the 1980s as TBT application reached its peak. Following legislation in 1987 banning the use of TBT on small boats (<25m) improvements were observed in the Itchen Estuary and to a lesser extent in the upper and mid Hamble (less evident in the lower Hamble). Two sites in the Test display extremes in terms of TBT concentrations and clam responses. In the upper Test (low TBT) populations have remained abundant. Lower down the Test, at Cracknore, high levels of TBT have been sustained following the 1987 legislation (due to continuing contributions from commercial and naval vessels and boatyards). Here, evidence for recovery is equivocal. Even though new application on ships was scheduled to cease in 2003, existing TBT coatings are permitted until 2008. These inputs, coupled with persistent sediment loadings may delay ecological improvements for years. In the long-term, the TBT issue will subside; for the immediate future, however, further surveys will be needed to establish the prognosis for recovery of molluscan populations from TBT pollution.
Full report: SEPG2239
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