Brook Floater Conservation
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Brook Floater
Alasmidonta varicosa
Biology, Ecology and Conservation
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Basic Biology and Life History
The Brook Floater (Alasmidonta varicosa) is a small (<75mm), stream dwelling Unionid from Atlantic Slope drainages in the Eastern U.S. The shell of the Brook Floater is described as "trapezoidal to elliptical" (Nadeau 2008). The Brook Floater is a long-term brooder, which means it undergoes fertilization in the summer and holds onto the glochidia until the following spring or summer before releasing those glochidia. Because of its wide range, the Brook Floater is thought to be a fish host generalist. There has been some success in identifying fish hosts; fishes as diverse as Redbreast Sunfish (Lepomis auritus), Piedmont Darter (Percina crassa) and the Bluegill (Lepomis machrochirus) have been demonstrated in a laboratory to be potential hosts (North Carolina Department of Transportation 2007). Brook Floater are known for their "hooked" glochidia (Haag 2012 - see photos of these from Barry Wicklow), which are presumed to be well-adapted for latching onto hosts.
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FUN FACTS
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Brook Floater are known to "gape", or relax it valves when removed from water, which exposes their cantaloupe- colored foot (Nadeau 2008).
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Brook Floater may live 15 or more years!
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Brook Floater are sometimes called "swollen wedgemussel".
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Freshwater mussels are important to clean water and fish habitat. As filter feeders, they eat algae and bacteria in the water to clean our streams and ponds.
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Photos Courtesy of Ayla Skorupa
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Photo Courtesy of Ayla Skorupa
Ecology
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Very few studies have been conducted to describe the ecology (biotic and abiotic interactions) of Brook Floater. Brook Floater typically inhabits streams and rivers with low to moderate flow velocity (Nadeau 2008, Haag 2012). Additionally, stable substrates (i.e. gravel) and the presence of large boulders are typical of Brook Floater habitat. Therefore, Brook Floater is rarely found in headwater or other high gradient streams (Nadeau 2008). However, a study of Brook Floater microhabitats found strong associations with medium sandy (0.25-1.0 mm) substrates (Strayer and Ralley 1993). The authors discuss the disparity between their findings and previous studies (i.e. affinity for gravel habitat) and caution the use of microhabitat factors in describing Unionid habitat relations. Seasonal behaviors of Brook Floater related to burial in sediments are not well described, although Brook Floater is reported to remain buried in sediment during the summer (presumably after fertilization occurs) and emerge from substrates during the winter (Bogan 2002, Haag 2012). Similar to a closely related species, the Dwarf Wedgemussel (A. heterodon), Brook Floater has affinities for stream with low calcium concentrations (Strayer et al. 1993).
Conservation status
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The Brook Floater has been suggested to be in decline across its range in the Eastern United States and there is both direct and indirect evidence to support this claim. It is currently listed as a species of greatest conservation need (SGCN) in 94% of the states within its range and was petitioned for Federal listing in 2011. Declines in density were found the in Upper Susquehanna River Basin from 1965-1997 (Strayer et al. 1999). Currently, there is a U.S. Fish and Wildlife (USFWS) Species Status Assessment underway to determine its federal listing status. Additionally, a Regional Conservation Need Grant was awarded to Barry Wicklow and colleagues to collect all available data to assess potential threats across its range.
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Probable Threats and Stressors
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Altered hydrology and fragmentation, especially due to dams
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Riparian habitat (and buffer) modification
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Effluent input to stream, especially via acid mine drainage
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Climate change and associated temperature and flow stressors
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Photos Courtesy of Ayla Skorupa
More Information on Brook Floater can be found here
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References
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Bogan AE. 2002. Workbook and key to the freshwater bivalves of North Carolina. North Carolina Museum of Natural Sciences, Raleigh, USA.​
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Eads CB, Raley ME, Schubert EK, Bogan AE and JF Levine. 2007. Propagation of freshwater mussels for release into North Carolina waters. North Carolina Department of Transportation.
Haag WR. 2012. North American Freshwater Mussels: Natural History, Ecology and Conservation. Cambridge University Press, New York, New York. 505pp.
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Nadeau EJ. 2008. Freshwater Mussels and the Connecticut River Watershed. Connecticut River Watershed Council, Greenfield, Massachusetts. 132pp.
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Strayer DL and J Ralley 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia), including two rare species of Alasmidonta. Journal of the North American Benthological Society 12:247-258.
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Strayer DL and AR Fetterman. 1999. Changes in the distribution of freshwater mussels (Unionidae) in the Upper Susquehanna River Basin, 1955-65 to 1996-97. American Midland Naturalist 142:328-339.
Brook Floater Conservation Partners
For more information,
email: bfwgwebpage@gmail.com
