Carolina heelsplitter mussel is helping monitor health of state’s rivers
CLEMSON — The Carolina heelsplitter’s name evokes painful imagery, but the name of this freshwater mussel is a misnomer. The species doesn’t actually have the sharp shell edges like other mollusks that might cause that injury.
But while its name may not be accurate, the Carolina heelsplitter is accurate when it comes to gauging the quality of water resources in the states it calls home.
Freshwater mussels are broadly viewed as a reliable indicator species of environmental change, and scientists consider the heelsplitter — the only federally endangered mussel species in South Carolina — particularly sensitive to shifts in water quality.
Clemson University freshwater ecologist Cathy Jachowski likens the heelsplitter to “a canary in a coalmine” in the way it acts as a warning sign of something amiss in the environment.
“Coalminers would go down into mineshafts and literally carried a canary — a bird in a birdcage — down with them,” said Jachowski, an assistant professor in Clemson’s department of forestry and environmental conservation. “Underground you don’t have as much fresh air moving, and toxic gases, like methane and carbon monoxide, can accumulate. Canaries are sensitive to changes in air quality and would get sick before the miners, providing an early signal of danger that saved many lives.”
Likewise, when heelsplitter populations aren’t thriving or reproducing, it serves as a harbinger of diminishing water quality for South Carolina’s rivers and streams.
Through a National Fish and Wildlife Foundation grant, Jachowski is working to identify habitat requirements to inform restoration and species recovery for the freshwater mussel — a bivalve similar to a clam one might find in a saltwater habitat — that lives in rivers and streams in South Carolina and a small portion of North Carolina.
“Most people have probably never heard of a heelsplitter; probably most people will never see one in their entire lives,” she said. “But we think of our rivers and streams of South Carolina as really valuable resources, and with this project the heelsplitter is kind of the tool or the means we’re using to learn more about the condition of those resources.”
One reason for the heelsplitter’s relative anonymity is its scarcity. First described in the mid-1800s, it was seen so rarely thereafter it was thought to have gone extinct. In the 1980s, the species was rediscovered but with few remaining in the wild — survey data compiled in 2012 identified 154 individuals spread throughout 11 surviving populations.
“This number is conservative due to survey methodologies used, but it gives you an idea of the plight of the heelsplitter,” said Morgan Wolf, a U.S. Fish and Wildlife Service biologist based in Charleston.
Extremely difficult to spot, the heelsplitter lives in the substrate — the material that rests at the bottom of a river — and young heelsplitters can be as small as 1 centimeter, while the largest members of the species are up to only four inches in size.
Once stabilized in the substrate, heelsplitters use siphons to pull plankton out of the water to feed, in the process filtering impurities out of the body of water where they live.
They also rely directly on their habitat to reproduce. Sperm are released by males into the water and enter females through a siphon to be fertilized. The eggs develop into glochidia — so small they might be confused with a grain of sand — and females must find fish to transfer their young to the environment, ejecting glochidia to latch onto the fish’s gills where they are a parasite for anywhere from a couple of days to a couple of months.
“It doesn’t hurt the fish, but the fish carries them and the baby mussels feed off that blood supply and eventually drop off, burrow in the substrate and continue on like adults,” Jachowski said.
Because of the many variables involved in the heelsplitters’ reproducton, there are also numerous factors that can disrupt the process, such as a lack of females in a given area, inability to find the right fish to transport the glochidia or habitat pollution that poisons mussels.
“Because the mussels are filter-feeding, they’re also pulling everything that’s not good in the water into their bodies: contaminants, heavy metals, pesticides or herbicides, for example,” Jachowski said. “For all those reasons, when we find a diversity of mussels that are in good shape, it tells us the water quality is good, the habitat is good and every species that’s supposed to be there is probably doing well.”
In contrast, when a population is declining or disappearing rapidly, it indicates to scientists that negative changes could be occurring in the environment.
Like many other native freshwater species, the Carolina heelsplitter is losing ground because humans occupy more and more of its traditional habitat. Urban development, such as residences, roads and wastewater treatment facilities, creates a problematic web of issues that degrade aquatic habitats.
“Increases in construction of impervious surfaces and discharge of wastewater treatment effluent lead to unnatural, flashy stream hydrology and lethal levels of ammonia and other nutrients in receiving waters, respectively,” Wolf said. “Although these types of impacts are harmful to most aquatic species, they are particularly so for mussels which are anchored in place and must filter water to breathe, eat and reproduce.”
Jachowski’s grant project has four components. First, she is working with researchers at The Wilds in eastern Ohio to develop a tool to detect heelsplitters from water samples by isolating genetic material, or environmental DNA (eDNA), shed from their bodies into the river.
“In other states, we’ve used eDNA to identify populations of other declining river species, like hellbender salamanders, without having to disturb any animals or their habitat,” said Stephen Spear, director of wildlife ecology at The Wilds. “We filter a liter of water from the river and then use established lab techniques to extract all the DNA caught on the filter that came from the river water. For this project, we’ll identify a short stretch of DNA sequence unique to the Carolina heelsplitter and use it to isolate any heelsplitter DNA that was floating in our water sample.
“There’s been a lot of eDNA work on amphibians and fish, but case studies with endangered mussels are much rarer, so we are hoping the lessons learned on this project will not only benefit the heelsplitter, but also additional mussel species in the future.”
Jachowski’s group will use the tool to sample about 100 sites in the Pee Dee River Basin, where the most thriving heelsplitter populations remain, hoping to use the efficiency of the process — rather than traditional snorkeling techniques — to uncover new populations.
Once the project team has isolated where heelsplitter populations occur, they will examine the habitats more closely, the project’s second component, to determine the optimal conditions for survival.
The project builds on federal and state efforts that have restored miles of federally designated critical habitat for the species by restoring fish passage at road crossing structures. Successful propagation facilities have also been implemented in both Carolinas.
“(Jachowski’s) project will save valuable and limited resources, particularly in the realm of species monitoring and status assessments, as well as augmentation efforts,” Wolf said. “Development of an effective and targeted Carolina heelsplitter eDNA protocol will allow managers to track species occurrence and also better predict which types of habitats are suitable for augmentation of animals produced at our facilities.”
The third component of the project is identifying impaired habitat around heelsplitter populations by using insect communities that also live in the substrate to map habitat quality.
Like heelsplitters, aquatic insect communities can also function as “canaries in a coalmine,” according to John Morse, emeritus professor in Clemson’s plant and environmental sciences department, since species that are less tolerant to pollutants can be a warning sign of pollution by their absence or reduced populations in an otherwise suitable habitat.
“By sampling insect communities in streams in the regions where Carolina heelsplitter occurs, we can determine which streams are likely polluted and investigate possible causes, enabling eventual resolution of the pollution problems,” Morse said. “We can also determine streams that have healthy, sustainable ecological integrity and possibly are suitable for propagation of Carolina heelsplitter.”
Morse will advise students working on the aquatic insect component of Jachowski’s project to sample and identify species of the insect communities in streams of the Carolina heelsplitter region and use the resulting community profiles to identify impaired stream segments and likely causes of their impairment.
Finally, once the team has identified impaired habitats, it can use that information to prioritize actions that can be implemented on the landscape to improve and restore habitat.
While that habitat improvement is directly aimed at benefitting the heelsplitter, it would in turn improve the water quality of South Carolina’s rivers and streams where it is found. The Pee Dee River, for example, is known for its rich biodiversity, with an array of mussels, insects, fish and amphibians that live there.
“If we can identify actions that benefit habitat for heelsplitters, it’s very likely those actions are going to benefit everything else in that waterway,” Jachowski said. “People may not ever see a freshwater mussel in their lives, but most people will fish or wade or swim or boat on a stream, and most people find those experiences really pleasant. They enjoy it, and they want to know that water is clean and healthy for them and for their children.
“I really view this work as using the heelsplitter as a sentinel for whether we’re taking good care of those waterways. Not only will it benefit other species of fish and wildlife, it’s going to benefit all the people living around these waterways as well.”