Invasive alien species in Switzerland - Schweizer ...

6 > Molluscs – Mollusca 115
The freshwater snail Potamopyrgus antipodarum (Gray) (Hydrobiidae) (see Fact
Sheet) is one of the few long-distance invaders in this group. It is native to New Zealand
and has been spread around the world probably with ballast water between freshwater
systems and on ornamental aquatic plants. Haynes et al. (1985) have suggested
another pathway as they have shown that P. antipodarum can survive a six-hour passage
through the gut of a trout and produce live young shortly afterwards. It is very
likely to induce ecosystem changes because of its enormous numbers in some places.
Two Physella species, Physella acuta (Draparnaud) and P. heterostropha (Say) (Physidae),
have been introduced into Switzerland. The latter species is of North American
origin, but the origin of the former species is disputed, although it probably originates
in south-western Europe. Since P. heterostropha is cold-tolerant, the expansion of its
range could lead to competition with native snails. While Turner et al. (1998) state that
the two species are morphologically distinct and occur together in some parts of Switzerland,
Anderson (2003) records the two species as synonyms.
Two alien species of Planorbidae, Gyraulus parvus (Say) and Planorbarius corneus
(L.), probably cause no concern, because the former is a rare species of North American
origin and the latter is a native species in Europe. It is likely that P. corneus cannot
establish populations in Switzerland, because of unsuitable climatic conditions. However,
it is found frequently, probably released from aquariums or transported by birds
from garden ponds.
6.2 Bivalves (Bivalvia)
There are only three introduced and established bivalves, but they are of concern,
because of their high abundance and feeding behaviour.
The two Corbicula species (Corbicula fluminea (O.F. Müller) and C. fluminalis (O.F.
Müller)) are very similar, so that they are discussed together (see Fact Sheet). Hakenkamp
and Palmer (1999) have demonstrated the strong influence Corbicula spp. have on
ecosystem functioning by linking pelagic and benthic processes as a result of their
intense filter feeding activity.
The zebra mussel Dreissena polymorpha (Pallas) (Dreissenidae) (see Fact Sheet) is
one of the most widely cited case studies of a freshwater invader. Whereas the species
is often considered to be beneficial in Europe, especially as a food source for diving
ducks, it is inflicting huge costs to the USA and Canada in the Great Lakes area. The
transformation of freshwater ecosystems by D. polymorpha is documented by Strayer
et al. (1999) and Karateyev et al. (2002).
The 19 established alien mollusc species belong to very different groups, i.e. 14 families,
with only one or two species per family. However, the species can be considered
as belonging to a number of major groups. Seven species from four families of slugs
(Milacidae, Limacidae, Agriolimacidae and Arionidae) have been introduced into