Freshwater Mussels and Aquatic Snails

Mussels

Overview

Freshwater mussel assemblage from the Licking River, Photo by Monte McGregror

Freshwater mussels, also known as mollusks, are one of the most imperiled groups of animals in North America. There are 297 species and subspecies of mussels found in North America. Of the 103 species of mussels native to Kentucky, 20 have completely disappeared from the state, and 36 more are considered rare or endangered. Forty six species are on the Agency’s Species of Greatest Conservation Need list within Kentucky’s Wildlife Action Plan.  As of 2013, there are 27 species in Kentucky that are listed as federally endangered or threatened (2 are candidates for listing). Kentucky has significant populations in many rivers, including over 70 species in the Ohio, Green, and Cumberland River systems. Mussels have been declining since modern civilization began to bring about habitat changes. This process has been greatly accelerated in the last 100 years, resulting in the listing of the species.

Biology

Plain pocketbook, Lampsilis cardium, mussel with lure, Photo by Monte McGregor

Freshwater mussels are soft-bodied animals enclosed in two shells connected by a hinge. These animals live buried in gravel, sand, or mud at the bottom of lakes, ponds, streams, and rivers. All mussels are filter feeders. With its foot buried in the bottom, a mussel draws fresh water carrying oxygen and nutrients while deoxygenated water and waste are expelled. The mussel’s food consists of bacteria, plankton, and detritus. Unused food particles are distributed back to the stream bottom as “pseudofeces”. Freshwater mussels have a complicated life cycle, and are dependent on connecting with a host fish. Mussels have some fascinating ways to attract their fish hosts: lures, packets of larvae, nets, scented packets, etc. Little is known about the juvenile mussel life stage. It is thought to be the most sensitive stage in the life cycle of a freshwater mussel. Mussels reach sexual maturity in 1 to 4 years. Each year the mussel lays down a winter growth line, allowing biologists to age a species. Mussels probably have the longest life spans of any of the freshwater invertebrates. Some of the thicker shelled river species of mussels have a life span of 20 to 100 years.

Why are mussels important?

Cultured and tagged mussels of the endangered pink mucket, Lampsilis abrupta, and the black sandshell, Ligumia recta, released in the Green River, Photo by Monte McGregor

Freshwater mussels are a renewable resource. They serve as an important food source for many aquatic and terrestrial animals. Mussels improve water quality by filtering out contaminants, sediments, and nutrients from our rivers and streams. Mussels also function as environmental indicators. They are sensitive to toxic chemicals and serve as an early warning system that alerts us to problems with water quality. Mussels are used in the cultured pearl and jewelry industry. The annual value of mussel shells to the shell industry has been between $40 and $50 million. Conservation, protecting, and enhancing mussel habitat is good for all aquatic species. High diversity mussel populations are indicators of a healthy stream for all species. Efforts are also underway in Kentucky to propagate rare and endangered mussels for augmentation and enhancement of native populations. KDFWR established the Center for Mollusk Conservation in 2002 with its mission to conserve and manage declining mussels. For more info, see the Center for Mollusk Conservation Brochure.

Conservation

Protecting and enhancing mussel habitat is good for all aquatic species. Diverse mussel populations are indicators of healthy streams for all species.  Efforts are also underway in Kentucky to propagate rare and endangered mussels for augmentation and enhancement of native populations. KDFWR established the Center for Mollusk Conservation in 2002 with its mission to conserve and manage declining mussel.

For more info, see the Center for Mollusk Conservation Brochure.

Aquatic Snails

Overview

Elimia sp. (aquatic snail) from the upper Cumberland River, Photo by Monte McGregror

Aquatic snails, also known as Gastropods, are another group of animals with special concern. In a 2013 review of the snails of the United States and Canada, the authors identified 703 species of freshwater snails representing 16 families and 93 genera (Johnson et al. 2013). Sixty-seven species are considered extinct, or possibly extinct, 278 are endangered, 102 are threatened, 73 are vulnerable, 157 are currently stable, and 26 species have uncertain taxonomic status. Of the entire fauna, 74% of gastropods are imperiled (vulnerable, threatened, endangered) or extinct, which exceeds imperilment levels in fishes (39%) and crayfishes (48%) but is similar to that of mussels (72%) (Johnson et al. 2013). According to Johnson et al. (2013), there are 65 species of native snails listed from Kentucky (9.2% of the North American Fauna), representing 11 families: 47 species are currently stable (72%), 2 are AFS endangered (3%), 3 are AFS threatened (4%), 1 undetermined, 10 vulnerable (15%), 1 extinct, and 1 possibly extinct. The most diverse Families in Kentucky are the Pleuroceridae (21 species) and Planorbidae (13 species).

Biology

Snails have a cone-shaped, spiral or coiled shell, a foot for moving, and a radula (teeth like structures for feeding). They are mostly herbivores or scavengers and typically breathe underwater with gills or an internal air-filled type of lung. Many snails are restricted to a certain type of habitat, such as a lake, river, spring, creek, swamp, or other type of aquatic habitat. Gastropods often live in specialized habitats, such as springs or short segments of streams, and are therefore highly susceptible to habitat loss and degradation.

Conservation

Twenty-eight percent (28%) of the snails are imperiled to some extent. However, little is known about life history, habitat requirements, current distribution, and other factors that may limit population numbers. A limited amount of work has been done at the Center for Mollusk Conservation (which currently cultures and propagates freshwater mussels and snails) to propagate a few species of snails (examples include Lithasia and Pleurocera).

For more information, see Johnson, P.D., A.E. Bogan, K.M. Brown, N.M. Burkhead, J.R. Cordeiro, J.T. Garner, P.D. Hartfield, D.A.W. Lepitzki, G.L. Mackie, E. Pip, T.A. Tarpley, J.S. Tiemann, N.V. Whelan, and E.E. Strong. 2013. Conservation Status of Freshwater Gastropods of Canada and the United States. Fisheries 38(6): 247-282.