The Carolina heelsplitter is a rare species of freshwater mussel endemic to the Carolinas. It was federally listed as endangered in 1993, and in 2002, six critical habitat units (one in North Carolina, five in South Carolina) were designated for the species. Recent survey efforts documented only 216 individuals range-wide. Ongoing recovery efforts are aimed at monitoring population numbers and habitat conditions, protecting and restoring habitat (mostly through road crossing replacements and bank stabilization), as well as propagating and augmenting wild populations. In addition, research projects studying life history characteristics and genetic considerations are currently underway.
Poor water quality and habitat conditions have led to the decline and loss of populations of the Carolina heelsplitter and threaten the remaining populations. Studies show that freshwater mussels, especially in their early life stages, are extremely sensitive to many of the pollutants (chlorine, ammonia, heavy metals, etc.) commonly found in municipal and industrial wastewater releases. Impoundments (dams) and improperly designed culvert road crossings impact the quality and stability of remaining stream reaches by affecting natural stream flow, temperature, and water chemistry. Agriculture (both crop and livestock) and forestry operations, roads, residential areas, golf courses, and other construction activities that do not adequately control soil erosion and runoff into streams contribute excessive amounts of silt, pesticides, fertilizers, heavy metals, and other pollutants that suffocate and poison freshwater mussels. The alteration of floodplains or the removal of forested stream buffers can be especially detrimental. Flood plains and forested stream buffers help maintain water quality and stream stability by absorbing, filtering, and slowly releasing rainwater. This also helps recharge groundwater levels and maintain flows during the dry months.
The Carolina heelsplitter is a medium-sized freshwater mussel similar in appearance to other species on the Atlantic Slope. Only highly trained biologists are able to differentiate this species from others found within its range.
Size and shape
- ?The largest known Carolina heelsplitter specimen measured 4.6 inches (116.8 millimeters) in length.
- The species has an ovate, trapezoid-shaped, unsculptured shell.
Color and pattern
- ?The shell’s outer surface varies from greenish brown to dark brown in color, with shells from youngers specimens having greenish coloration with brown rays.
- The nacre (inside surface of the shell), is often pearly white to bluish white, grading to orange in the area of the umbo (hinge).
In the fall, male Carolina heelsplitter release sperm into the water column, which is then taken in by siphoning females. Eggs are fertilized and the resulting larvae held in the female’s gills until early the following spring, when around March the female releases the larvae in loose packages (conglutinates) into the water. These are eaten or otherwise come into contact with small fish species, where the larvae attached to the gills and fins of the fish. During this parasitic stage, larvae use the blood supply of the fish to develop internal tissues and metamorphose into juvenile mussels. The swimming fish also help disperse mussels upstream and downstream of their parent location. After about three weeks, the young mussels fall off the fish and bury in stream sediments, where they start to feed and grow. Heelsplitter become sexually reproductive around 3 years of age and are at that time considered adults.
Individuals have three distinct life stages, larvae (glochidium), juvenile, and adult
Carolina heelsplitter are moderately long-lived, with individuals living on average approximately 15 to 20 years. For reference, some mussel species can live well over 100 years, while others are thought to live only 5 years or so.
The Carolina heelsplitter requires well-oxygenated water with low amounts of pollutants. Stable stream bottoms appear to be critical to the species. Typically, stable areas occur where the stream banks throughout the watershed are well-vegetated with trees and shrubs.
A natural body of running water.
Like other freshwater mussels, the Carolina heelsplitter feeds by siphoning and filtering food particles including algae and bacteria from the water column, thereby cleaning our streams and rivers.
The Carolina heelsplitter, like other species of freshwater mussels, is relatively sedentary. However, individuals are known to move vertically and horizontally in the stream bed in response to threats (drought, storms, habitat disturbance, etc.) and other stimuli (seasonal changes, etc.).
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