Distribution of Aquatic Mollusks in Minnesota

Dawley, Charlotte

The distribution of mollusks is influenced by both geographical and ecological factors. The separation of one drainage system from another, and barriers such as water-falls within a single drainage serve to limit the geographical distribution of mussels. Snails can surmount such barriers more easily. Ecological factors, such as size, current, chemical content, kind of bottom, and presence of vegetation are important in the distribution of both snails and mussels. The three drainage systems in Minnesota are described and the mussels in each are listed. The largest number of species was found in the Mississippi River south of St. Anthony Falls which has apparently proved a barrier to the Northward migration of many of these species since only eight were found above the falls while 27 species were found at Fort Snelling a few miles below and 20 species were found in the upper St. Croix drainage. The rivers of the St. Lawrence drainage had the smallest number of species. Most species of mussels in Minnesota apparently migrated into the state from the lower Mississippi River after the retreat of the glacier, but Anodonta marginata, found in many northern lakes, and Elliptio complanatus, found only in Lake Superior in Minnesota are species characteristic of the St. Lawrence drainage and apparently have come in through the Great Lakes. There is a similarity between the mussels of the Minnesota and Red Rivers which is explained by their long post-glacial connection. The waters of Minnesota are divided ecologically into flowing waters and standing waters. The flowing waters are further subdivided into small creeks, small rivers, medium-sized rivers, and large rivers, and the standing waters into ponds, soft-water lakes, medium-hard lakes, prairie hard-water lakes, and river-lakes. The mollusks in each are listed. Although some species of mussels, such as Lampsilis siliquoidea and Anodonta grandis can live in a wide variety of habitats, most species are adapted to a more or less limited environment. Anodonta marginata was found only in lakes, Anodontoides ferussacianus only in lakes and small rivers, Lasmigona compressa only in small rivers. Amblema costata, Fusconaia flava, and Strophitus rugosus also seemed to prefer small rivers. Several species were found only in larger rivers in Minnesota, although farther south they were found also in medium-sized and even small rivers. Most snails found in lakes, ponds, and even in small rivers were lung breathing and belonged to the Order Pulmonata, although a few gill-breathing snails of the Order Ctenobranchiata, such as Valvata tricarinata, Amnicola limosa, and Campeloma decisum were common in large lakes. Most of the snails found only in rivers were gill-breathing, the most common one being Pleurocera acuta tracta. Only lung-breathing snails were found in Minnesota ponds, and usually not more than three different species in any one pond. Aplexa hypnorum, Gyraulus parvus, and Lymnaea exilis were the most common species in the more or less temporary coniferous forest pools of Itasca Park, while Helisoma trivolvis and Physa gyrina were more common in the less shaded and more permanent ponds in other parts of the state. In lakes the common species were Amnicola limosa, Helisoma antrosa, Helisoma campanulata, Lymnaea stagnalis appressa, Physa gyrina, and Valvata tricarinata. Campeloma decisum was common in soft-water and medium-hard lakes, while in the prairie hard-water lakes in the western part of the state Lymnaea palustris and Lymnaea emarginata were abundant and varied. In river-lakes the river influenced the molluscan fauna in two ways-the number of species of mussels increased and the snails Pleurocera acuta tracta and Lioplax subcarinata appeared.

Distribution of Aquatic Mollusks in Minnesota

Series