Naturalisation of an introduced species, the Manila Clam, Tapes philippinarum, in Poole Harbour, UK.
The introduction of T. philippinarum (the Manila clam) into Poole Harbour in 1988 for aquaculture produced an unexpected environmental impact in the form of a naturalized fishery. It was thought that this non-indigenous species would be unable to reproduce, as low water temperatures would prevent the gonads from reaching full sexual maturity. However, the farmed population did successfully mature, spawn and produce viable spat. The spat settled around the harbour where a suitable substrate (i.e., soft mud) could be found. This occurred in successive years and a naturalized population developed and successfully reproduced. By 1994, local fishers began to exploit the naturalized population and the fishery became licensed by the local fisheries managers. The fishery now supports 31 local fishers, landing approximately 250 tonnes of clams in 2002 with an estimated market value of CAD$1.88 million. A study of this unusual situation in Poole Harbour has been carried out over a three-year period and examination of the histological data confirms that the naturalized population is self-sustaining, and were the aquaculture of this species to be withdrawn from Poole Harbour, the naturalized population would remain in sufficient numbers to continue to support the fishery at its present level.