Freshwater Mussels of Florida

Family Dreissenidae – Falsemussels

Additional Bivalves in Inland Waters 405 Figure 12.2. Polymesoda caroliniana – Length 43 mm, UF 181786. Mouth of Suwannee River, Dixie County, Florida, 1987. Illustration by Susan Trammell. Range Polymesoda caroliniana is distributed along the Atlantic Coast from Virginia to northern Florida and on the Gulf Coast from Texas to peninsular Florida (Abbott 1974). Museum records indicate that it occurs as far south as Naples and the Everglades on the Florida Gulf Coast. Remarks In Florida Polymesoda caroliniana occurs in estuaries and coastal stream reaches both within and upstream of tidal influence. It inhabits warm, shallow waters in mud and sandy mud without macrophytes or coarse organic debris (van der Schalie 1933; Andrews and Cook 1951). Distribution of P. caroliniana may be limited by infaunal competition with Rangia cuneata where they co-occur (Swingle and Bland 1974). In tidal estuaries of southwest Florida, P. caroliniana occurred at salinities between 1–20 ppt and was most abundant at salinities of about 5 ppt (Montagna et al. 2008). Family Dreissenidae – Falsemussels The family Dreissenidae is represented by four species in marine, estuarine, and freshwater environments of the United States (Turgeon et al. 1998). Two species are native, Mytilopsis leucophaeata and Mytilopsis sallei, and two species are introduced, Dreissena polymorpha and Dreissena bugensis. Both native species occur in Florida estuaries, but only M. leucophaeata is known to inhabit some freshwater habitats. Dreissenids are small bivalves that are sessile and use byssal threads to attach themselves to a wide range of natural and man-made substrates. They are considered fouling species due to their tendency to form large colonies on seawalls, water control structures, docks, pipes, and boats; dreissenids are rarely observed living as solitary individuals. Additional Bivalves in Inland Waters 406 Introduced dreissenid species are known to have a major impact on native mussel populations by byssally attaching to their shells and competing for food and space (Strayer 1999a). When present in large numbers they have caused local extirpation of mussel populations (Martel et al. 2001; Haag 2012). Even more insidious is the fact that native mussel shells seem to be a preferred settling site for Dreissena polymorpha veligers (Ricciardi et al. 1996). After attachment of D. polymorpha, decline in mussel populations is almost immediate and once fouled, mussels can be extirpated in four to seven years (Martel et al. 2001). Dreissena polymorpha and Dreissena bugensis were introduced into NorthAmerica from Europe in the 1980s. Dreissena polymorpha was introduced into Lakes St. Claire and Erie in 1988 and rapidly spread across most of the eastern United States (Mackie and Schloesser 1996). Dreissena bugensis was found in the Erie Barge Canal and eastern Lake Erie in 1991 and had spread as far west as Lake Mead, Nevada, by 2007 (Mills et al. 1996; Stokstad 2007). Both species are believed to have been introduced into North America as veligers via ballast water pumped from ocean-going vessels originating in Ukraine (Mackie and Schloesser 1996). Dreissena polymorpha and Dreissena bugensis have entered Florida but have not been found in open waters. Live D. polymorpha held in aquaria by individuals were destroyed by FWC. Dead D. bugensis have been found in the intake pipes of boats transported to Florida from Lake Mead, Nevada. Environmental conditions in some Florida freshwater habitats, including such diverse water bodies as Juniper Springs, Wekiva River , and Lake Okeechobee, are suitable for colonization by D. polymorpha (Hayward and Estevez 1997). Veliger transport in bilge water and live wells of boats is a likely pathway for introduction. Mytilopsis leucophaeata (Conrad 1831) Dark Falsemussel Description Length to 25 mm; shell byssate, moderately thin, elongate, narrow to bluntly pointed anteriorly, broadly rounded posteriorly; umbo positioned anteriorly, narrowly rounded to bluntly pointed, directed anterioventrally; ventral margin nearly straight, slightly convex posteriorly in large specimens; byssal notch slightly developed; dorsal margin broadly convex from umbo to posterior margin; posterior margin broadly rounded; periostracum cream-colored to dark brown, sometimes with zigzag color pattern similar to Dreissena polymorpha, especially in juveniles, also with thin concentric lines; apophysis small, rounded, occasionally pointed, closely associated with septum; pallial and extrapallial regions porcellaneous; nacre white with grayish areas posteriodorsally in some specimens (Figure 12.3). Additional Bivalves in Inland Waters 407 Figure 12.3. Mytilopsis leucophaeata – Length 22 mm, UF 388524. St. Johns River, Florida, June 2002. Illustration by Susan Trammell. Range Mytilopsis leucophaeata is distributed along the Atlantic Coast from New York to Florida and on the Gulf Coast...