- Taxon: Freshwater mussel
- Range: James, Chowan, Roanoke, Tar, Neuse, Cape Fear, Pee Dee, Catawba, Edisto, Savannah, Ogeechee, and Altamaha River basins in Virginia, North Carolina, South Carolina, and Georgia
- Status: Proposed for listing as threatened under the Endangered Species Act on October 11, 2018.
The shell of the Atlantic pigtoe is a chunky, rhombus shape, like that of a pig’s hoof/toe. There is a distinct posterior ridge. The outer surface of the shell is yellow to dark brown and parchment-like, while the inner layer is iridescent blue to salmon, white, or orange. Although larger specimens exist, the Atlantic pigtoe rarely exceeds 2 inches in length.
Young individuals may have greenish rays across the entire shell surface. When collected fresh, the interior surface (nacre) in the shell tends to be salmon colored and sometimes iridescent. Atlantic pigtoe has interlocking hinge “teeth” on the inside of the shell to help keep the two valves in proper alignment.
The preferred habitat of the Atlantic pigtoe is coarse sand and gravel, and rarely in silt and detritus. Historically, the best populations existed in small creeks to larger rivers with excellent water quality, where flows were sufficient to maintain clean, silt-free substrates.
The life cycle of the Atlantic pigtoe, like most freshwater mussels, is complex, relying on host fish for successful reproduction. Male Atlantic pigtoe release their sperm into the water column where it is siphoned in by the female Atlantic pigtoe mussels. Once fertilization has taken place in the gills of the female mussel, mature microscopic glochidia (larva) are released by the females where they must attach themselves to the gills and/or fins of fish hosts to continue developing. Atlantic pigtoe are tachytictic (short term breeders) that usually release their larvae by July or August.
Each mussel species has specific fish species (host fish) that are needed by the glochidia to keep growing to ultimately transform into juveniles. After a few weeks of living as parasites, they drop off and land on the river bottom where they grow into adults. Host fish for the Atlantic pigtoe include the rosefin shiner (Lythrurus ardens), creek chub (Semotilus atromaculatus), longnose dace (Rhynichthys cataractae), white shiner (Luxilus albeolus), satinfin shiner (Cyprinella analostana), bluehead chub (Nocomis leptocephalus), rosyside dace (Clinostomus funduloides), pinewoods shiner (Lythrurus matutinus), swallowtail shiner (Notropis procne), and Mountain Redbelly Dace (Chrosomus oreas). The time period for glochidia to develop varies between 30 to-60 days, and depends on the host fish.
Freshwater mussels are living filters, known as suspension feeders because they eat algae, bacteria, and other microscopic matter they filter out of the water. Juveniles likely pedal-feed in the sediment, whereas adults filter-feed from the water column. When they feed, they help keep the water clean by removing pollutants that could potentially harm aquatic animals, birds, land-dwelling animals, and people who may drink the water.
This species originally ranged from the James and Chowan River basins in Virginia, the Roanoke, Tar, Neuse, Cape Fear, Pee Dee, and Catawba River basins in North Carolina, the Edisto River Basin in South Carolina, and the Savannah, Ogeechee, and Altamaha River basins in Georgia.
Counties where the species has been known to occur
- Prince Edward
- Jeff Davis
- Ben Hill
The Atlantic pigtoe can be found today in seven of 12 river basins the mussel used to occupy. The current distribution includes the James, Chowan, Roanoke, Tar, Neuse, Cape Fear and the Pee Dee River basins. Historical records (>20 years) exist in the Catawba, Edisto, Savannah, Ogeechee, and Altamaha River basins.
Adult mussels are easily harmed by toxins and declines in water quality from pollution because they stay in one place. Pollution may come from specific, identifiable sources such as factories, sewage treatment plants and solid waste disposal sites or from diffuse sources (non-point pollution sources) like runoff from cultivated fields, pastures, cattle feedlots, poultry farms, mines, construction sites, private wastewater discharges, and road drainage. Pollutants can cause changes in water chemistry that seriously impact aquatic species by reducing water quality and may directly kill mussels, reduce the ability of surviving mussels to have young, or result in poor health or disappearance of host fish. A 2003 study revealed that levels of ammonia far below EPA maximum allowed concentrations caused the death of glochidia after only 24 hours of exposure, which led to a change in allowable ammonia concentrations in surface waters.
Sediment is material suspended in water that usually is moved as the result of erosion. Although sedimentation is a natural process, poor land use practices, dredging, impoundments, intensive timber harvesting, heavy recreational use, and other activities may accelerate erosion and increase sedimentation. A sudden or slow blanketing of the river bottom with sediment can suffocate freshwater mussels because it is difficult for them to move away from the threat. Increased sediment levels may also make it difficult for Atlantic pigtoe to feed, which can lead to decreased growth, reproduction, and survival.
Dams affect both upstream and downstream mussel populations by disrupting natural flow patterns, scouring river bottoms, changing water temperatures, and eliminating habitat. The Atlantic pigtoe, a mussel adapted to living in river currents, cannot survive in the still water impounded behind dams.
Atlantic pigtoe also depend on their host fish as a means of moving upstream. Because dams are barriers that prevent fish from moving upstream, they prevent mussels from moving upstream. Upstream mussel populations then become isolated from downstream populations. This isolation leads to small, unstable populations that are more likely to die out.
How you can help
- Individuals can do a number of things to help protect freshwater species, including:
- Conserving water to allow more water to remain in streams.
- Using pesticides responsibly (especially around streams and lakes) to prevent runoff into mussel habitats.
- Controlling soil erosion by planting trees and plants to avoid runoff of sediments into freshwater areas.
- If you live near a stream, be careful not to disturb the stream bottom; you may be damaging a freshwater mussel’s home.
- Don’t pick up any mussels that you may see in a stream. It may be one of the last few members of its species on the planet.
- Help your family find ways to reduce the amount of chemicals that you pour down the drain in your home or use on your lawn or garden.
- Check to see if the water draining off your roof or driveway flushes directly into a stream. Plant a garden to catch the water before it enters the stream. The garden will act like a filter and help purify the water.
- Recycle as much as you can to reduce the amount of waste you place in the garbage.
- Support conservation efforts that protect these unique animals and the habitats they live in.
- Become a biologist and discover new ways to help protect freshwater mussels and other wildlife.
- Learn more about how the destruction of habitat leads to loss of endangered and threatened species and our nation’s plant and animal diversity. Discuss with others what you have learned.
- Support local and state initiatives for watershed and water quality protection and improvement.
- South Carolina DNR factsheet
- North Carolina Wildlife Resources Commission species profile
- North Carolina Wildlife Resources Commission freshwater mussel and endangered fish glossary
- Georgia DNR factsheet
- Freshwater mussel activity book and learning resource
Federal Register notices
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