Tributyltin pollution and the bioindicator Nucella lapillus : population recovery and community level responses.
The detrimental effects of tributyltin (TBT) have been recorded on many marine organisms. As a result
the UK Government imposed a partial ban on the use of organotin antifouling paints on boats less
than 25 m in length, in 1987. In 1988 the Isle of Man Government followed suit introducing a licensing
procedure restricting all uses of organotins.
At concentrations less than 0.5 ng Sn/I female Nucella lap/Nus develop imposex - the superimposition
of male sexual characteristics. To date there have been few studies measuring the recovery of Nucella
populations after the introduction of restrictions. This study produces evidence of the extent of
recovery in Nucella populations from sites in the south-west of England and on the Isle of Man. The
recovery observed was measured by decreasing values of relative penis size, vas deferens sequence
and the percentage of sterile adult females in the population. Following the 1987 ban the recovery of
Nucella populations in the south-west has shown a linear response allowing predictions to be made for
the time scale of complete recovery. In addition concentrations of TBT in the water and tissues of
selected indicator organisms also showed decreases. Around the Isle of Man the illegal use of TBT
paints was identified and later discouraged by the Marine Administration which was followed by a
reduction in TBT concentrations in the water at sites around the Isle of Man. Levels of imposex in
dogwhelk populations around the Isle of Man have decreased.
Although effects of TBT on Nuce/la have been well documented at the cellular and individual level, the
knock on effects on the community have not been investigated. Manipulative field experiments were
used to demonstrate the role of Nucella lapd/us in structuring shore communities to allow predictions of
the effect of TBT to be made. Rather than using the traditional approach of fences and cages,
dogwhelks were removed by hand on regular visits to experimental sites creating treatments with
reduced abundances of dogwhelks akin to shores affected by TBT. The role of Nucel/a was examined
at different stages of a cycle existing on moderately exposed Manx shores where Fucus vesiculosus
and Semibe/anus balanoides fluctuate in abundance. The removal of dogwhelks increased the
abundance of Semibalanus ba/anoides on the shore and as a result likelihood of algal escapes from
grazing by Patella vulgate also increased. In addition the removal of Nucela increased the size and
longevity of newly established Fucus vesiculosus clumps. In a factorial experiment the role of Patella
vulgate and Nucella lapillus were examined simultaneously. Nuce/la was found to have an significant
effect but less than that of Patella. The presence of Nucella did, however, mediate the effect of Patella.
In addition Nucella was found to have a direct effect on the level of Semibalanus balanoides settlement
in the field with the number of barnacles settling in cleared areas being reduced on areas which had
been previously occupied by Nucella.