Poor water quality and habitat loss are driving Ireland's terrestrial and freshwater snails, along with related species into extinction, according to new research by the National Biodiversity Data Center (NBDC), a three-year-old organization established to study that country's biodiversity.

The study (pdf) of nonmarine Irish mollusks found that of 150 species, one third are threatened with extinction. Two are now regionally extinct, five critically endangered, 14 endangered, 26 vulnerable and six near threatened. (These classifications are those of the IUCN Red List of Threatened Species, to which this report's data has been contributed.)

Of the 150 species in Ireland, 15 are invasive, including the zebra mussel (Dreissena polymorpha), which is outcompeting native swan mussels and duck mussels (Anodonta cygnea and A. anatina).

The extinct species include the lapidary snail (Helicigona lapicida), which was last observed in Ireland in 1968, and the mud pond snail (Omphiscola glabra), which the NBDC says was "lost to habitat destruction" in 1979.

Ireland's mollusks are of "international importance," according to the NBDC, which notes that several species exist in higher percentages in the country than anywhere else in the world. For example, at least one fifth of the global populations of both the silky snail (Ashfordia granulata) and Leiotyla anglica (a species with no common name) exist in Ireland.

Threats facing snails and other mollusks include pollution, agricultural drainage of wetlands, other habitat loss, climate change and invasive species.

Although the report doesn't examine the impact that declining mollusk populations could have on Ireland's ecology, snails and other species play several important roles in the environment: They are a primary food source for many animals and fish, and they help filter water to keep rivers and lakes clean. Despite this importance, mollusks are infrequently studied and represent the taxonomy "most affected by extinction," according to a paper published last year in Conservation Biology.

Image: Helicigona lapicida, a species now extinct in Ireland. Via Wikipedia