Population dynamics of naturalised Manila clams <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> in British coastal waters |
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Authors: | John Humphreys Richard W G Caldow Selwyn McGrorty Andrew D West Antony C Jensen |
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Institution: | (1) Old Royal Naval College, University of Greenwich, Greenwich, London, SE10 9LS, UK;(2) Centre for Ecology and Hydrology, CEH Dorset, Winfrith Technology Centre, Winfrith Newburgh, Dorchester, Dorset, DT2 8ZD, UK;(3) School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, Hampshire, SO14 3ZH, UK |
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Abstract: | The Manila clam Ruditapes philippinarum was introduced to Poole Harbour (lat 50°N) on the south coast of England in 1988 as a novel species for aquaculture. Contrary
to expectations, this species naturalised. We report on individual growth patterns, recruitment, mortality and production
within this population. On the intertidal mudflats the abundance of clams (>5 mm in length) varied seasonally between 18 and
56 individuals m−2. There appear to be two recruitment events per year and there were 6 year classes in the population. A mid-summer decline
in abundance was partly due to increased mortality but probably also a result of down-shore migration in response to high
water temperatures and the development of anoxic conditions. A winter fishery removes c 75% of clams of fishable size (maximum
shell length ≥40 mm) and c 20% of the annual production. The fishery depresses the maximum age and size attained by the clams
but appears to be sustainable. Clam mortality due to factors other than fishing is highest in late-winter to early spring.
The growth of the clams is intermediate in comparison with many published studies but remarkably good given their intertidal
position. As on the coasts of the Adriatic Sea, where the clam is also non-native, the Manila clam has thrived in a shallow,
eutrophic, lagoon-like system on the English coast. While the Poole Harbour population is currently Europe’s most northerly
reported self-sustaining, naturalised population, given forecasts of increasing air and sea temperatures it might be expected
that this species will eventually spread to more sites around the coasts of Northern Europe with associated economic and ecological
consequences. |
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