Introduction

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Nekola, J.C., M. Barthel, P. Massart, and E. North. 1999. Terrestrial gastropod inventory of igneous outcrops in Northeastern Minnesota. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 60 pp.

Introduction:

The terrestrial gastropod fauna of the Midwest includes a number of the rarest animal taxa in North America. This fact was recognized as early as the late 1800's when the Pleistocene Hendersonia occulta was discovered alive along the Upper Mississippi River valley (Pilsbry 1948). Since then, a number of Midwestern endemics or near endemics have been identified including Catinella exile, Catinella gelida, Discus macclintockii, Hawaiia n.sp., Stenotrema hubrichti, Vertigo hubrichti, Vertigo 'iowaensis , Vertigo mermacensis, and Vertigo morsei (Hubricht 1985, Frest 1990, Frest 1991). Previous investigations into terrestrial gastropod biodiversity in the upper Midwest have been largely limited to the Paleozoic Plateau ('Driftless Area') and the Iowan Erosional Surface in northeastern Iowa, and the Black Hills of South Dakota (Frest 1981, 1982, 1983, 1984, 1985, 1986a, 19866, 1987, 1990, 1991, Frest and Johannes 1991). As these areas were beyond the limit of Wisconsin glaciation, they were presumed to be the only potential refuges for glacial relict taxa However, investigations made from 1995 1998 from eastern Wisconsin to southern Ontario documented that these relicts were not as geographically restricted as previously believed.

Four habitats were found to harbor the bulk of important land snail species in this area (Nekola et al. 1996; Nekola 19986). Carbonate cliffs support populations of at least seventeen rare Michigan and Wisconsin taxa, nine of which are likely glacial relicts. The fauna of these sites, while bearing marked similarity to algific talus slope and maderate cliff sites of the Paleozoic Plateau, are unique and support a higher frequency of northeastern species at (or beyond) their normal range limits (Nekola et al. 1996). Fens harbor the European disjunct Euconulus alderi, the presumed glacial relicts Catinella exile, Vertigo elatior, and Vertigo morsel, plus at least two undescribed endemic taxa (Hawaiia n.sp. and Punctum n.sp.; Frest 1990). Tamarack sedge wetlands have also been found to harbor the critically endangered Vertigo nylanderi (last seen alive in 1949), plus Euconulus alderi and Vertigo elation Mafic or ultramafic igneous outcrops (basalts and serpentines) in northern Wisconsin and the Keweenaw Peninsula were found to support populations of Vertigo cristata and Vertigo paradoxa, both known from less than a U.S. dozen sites (Frest and Johannes 1991, Nekola 19986). A number of other regionally rare taxa, including Planogyra asteriscus and Zoogenetes harpa have also been found on these sites.

The conservation importance of these habitats transcends the rare species found within them. Approximately 1/3 of carbonate cliff sites in the western Great Lakes harbor 24 or more taxa (Nekola, in press A), a level of sympatry which has been identified as being of global importance for land snails (Tattersfield 1996). Algific talus slopes, lakeshore carbonate ledges, and calcareous open meadows also commonly harbor faunas of 17 or more taxa (Nekola, in press A). Carbonate cliff sites in eastern Wisconsin are also among the richest reported land snail sites at small spatial scales, with up to 21 taxa coexisting within 400 cm2, and 34 taxa within 100 m2 samples (Nekola, in press B). Based on these analyses, carbonate cliffs and related habitats in the Great Lakes region warrant inclusion among the most important habitats for molluscan biodiversity on a global scale. Unfortunately, land snail communities are among the most sensitive known to anthropogenic and other disturbances (Frest and Johannes 1995). Even as the conservation importance of these taxa and sites are being realized, they are being lost from development, agriculture, forestry, and recreational pressures (Frest 1991, Nekola et al. 1996, Nekola unpublished data). Like taxa of the tropical rain forest, local terrestrial gastropod species and communities of the Upper Midwest may be lost before the full extent of their existence is recognized.

This is particularly true in northeastern Minnesota, where anthropogenic impacts from forestry, recreation, and development are high. Almost nothing is known about the faunas associated with the west shore of Lake Superior. Hubricht (1985) identifies Minnesota as one of the most poorly known regions in the eastern U.S. for land snails. No species had previously been reported from Cook County, and only six have ever been recorded in total from Lake and St. Louis counties.

A concentration of mafic igneous outcrops exist in northeastern Minnesota along the Pigeon River and the western Lake Superior shore (Coffin and Pfannmuller 1988). These sites are one of the most important refugia for disjunct arctic and western Cordilleran vascular plants in eastern North America (Fernald 1925, Butters and Abbe 1953, Given and Soper 1981). North facing basalt cliffs along the Pigeon River support at least 16 Minnesota DNR listed taxa, while similar outcrops along the Lake Superior shore support populations of at least 11 additional listed taxa. Rare snails might also occur in these sites are they often coexist with plants given their similarly small minimum habitat requirements and effectively sessile nature at the landscape scale (Berry 1966, Frest and Johannes 1995).

This report summarizes the findings of a survey conducted during the summer of 1998 from igneous outcrops along the western Lake Superior shore in Cook, Lake, and St. Louis counties in northeastern Minnesota. Through this research, a better understanding of the nature of the terrestrial gastropods from this little known area is possible.

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