On Thursday 6 February 1997, there was a joint evening meeting between the Linnean Society and the Malacological Society at the Linnean Society rooms in London. The meeting was well attended by about eighty participants who heard accounts of molluscan invasions at three different temporal scales. Representing current molluscan invasions, Dr James Coupland of Montferrier sur Lez in France gave a talk "On the trail of the Giant African Snail" in which he discussed the biology, biogeography and ecology of the Giant African Snail which is invading several locations around the world. For recent historical invasions, Dr Richard Preece of the University of Cambridge talked on pleisticene and recent non-marine invasions in Europe. Mollusc invasions in deeper time were discussed by Noel Morris of the Natural History Museum in his talk entitled Molluscan Invasions - a palaeontological perspective. The meeting, organised by Georges Dussart and John Marsden, was followed by a wine-tasting in the library of the Linnean Society. Dr Preece gives here a synopsis of his talk.
 

European non-marine mollusc invasions -Pleistocene and Recent

Richard Preece, Zoology Department, Cambridge University.

During the last 2 million years or so, northern latitudes have experienced repeated shifts in climate from fully glacial to fully temperate conditions. Such oscillations have occurred with differing intensities and on very different timescales and have affected global sea-levels and consequently the palaeogeographical configuration of areas surrounded by shallow continental shelves. The biological consequences have been enormous. During cold stages, thermophilous taxa would have been displaced by arctic-alpine taxa and other cold-adapted species, which would then have been able to colonize places like the British Isles across areas that are now submerged. When the climate became temperate at the beginning of interglacial stages, thermophilous taxa, often those associated with woodland, were able to return. However, the composition and succession during each of these cycles were never exactly identical.

Notorious colonists, such as Corbicula fluminalis, were able to invade Britain during many, but not all, interglacial stages. For the Holocene, we have a much clearer idea of the pattern of colonization of land snails, than for earlier periods. Since this period covers the last 10,000 years, we can also use radiocarbon dating to provide a chronology to the faunal history and so assess the rapidity of spread by natural means. Synchroneity of events across parts of southern Britain suggested surprisingly rapid spread. Such a view is reinforced when we consider several modern invasions. Potamopyrgus antipodarum, introduced to Britain from New Zealand in the middle of the last century spread throughout much of the country in less than 75 years. Similarly rapid rates of spread are being witnessed by certain terrestrial taxa.

The slug Boetgerilla pallens has also shown huge expansions of its range within the last 20 years. Perhaps the belief that snails are the most pedestrian members of the animal kingdom requires reappraisal.