Nov/Dec 2016For Wildlife Watchers: Carolina Heelsplitterby Rob Simbeck
Carolina heelsplitter is a mussel found exclusively in some of North and South Carolina's river systems.
Imagine a visit to a planet facing an ecological crisis. Say as many as a tenth of its bird species were threatened or endangered. A fifth of its fish, reptiles and mammals, and a third of its amphibians - all endangered. And say half of its primates faced challenges to their very existence.
Well, this is that planet. Of course, not every endangered species makes a great poster child, but that makes them no less precious. Ask the people on the front lines, the biologists who study and attempt to bolster marginal populations at that place where natural history, politics and finance come together. Take the Carolina heelsplitter, a mussel found exclusively in some of North and South Carolina's river systems. One of its main advocates entered the picture at a crisis point.
"When I began working with the species in earnest, about six years ago," says Morgan K. Wolf, a biologist with the U.S. Fish and Wildlife Service in Charleston, "the prevailing thought was that the heelsplitter was beyond hope. As such, it was difficult to justify and get funding for heelsplitter-related recovery projects."
It's not easy to picture a creature with a rock-hard shell tucked away in sometimes-remote streams as vulnerable, but the Carolina heelsplitter proved to be just that. Even when it was first described for science in 1852, the heelsplitter had a limited presence. It was found then in the Catawba, Pee Dee, Saluda and Savannah river systems. Most species of mussels east of the Rockies were pulled from streams and rivers by people seeking to find pearls or sell them for the button business. Dams, pollution, channelization, development, agricultural and pesticide runoff and rising temperatures have all taken their toll since.
By 1993, the Carolina heelsplitter was listed as endangered, and in 2012 the USFWS reported that it turned up just 154 individuals in the 11 stretches of stream or river that held them.
"With approximately 154 individuals surviving in the wild," says Wolf, "I would certainly consider it the most endangered faunal species in the state, if not the most endangered species period. The largest population, in Flat Creek, which feeds the Lynches River, is comprised of about sixty-four individuals at last, best count." Another site held twenty-eight and others were found along the slate-belt portion of the piedmont, from Lancaster County through Lake Murray to J. Strom Thurmond Lake.
Heelsplitters are by no means unusual in that regard. According to The Nature Conservancy, about 70 percent of North American mussels are extinct or imperiled, and the introduction of invasive species further complicates the matter.
Carolina Heelsplitter - Lasmigona decorata
Description: Three to four inches long, ovate, brown shell, white to orange nacre.
Range and Habitat: Eleven surviving populations in streams and rivers in North and South Carolina.
Mating: Fresh, relatively clear running water.
Viewing Tips: Endangered. This is a species we shouldn't disturb.
This is a medium-sized mussel (the biggest known individual was 4.6 inches long, 1.5 inches wide and 2.7 inches thick) with an ovate shell ranging from greenish to dark brown. The nacre, or mother-of-pearl, is bluish-white to pearl white, taking on an orange hue as the individual ages. The "heelsplitter" designation reflects the fact that other members of the genus Lasmigona have large, sharp "wings" or shell edges that protrude from stream bottoms.
The Carolina heelsplitter requires cool, clean, well-oxygenated water and stable, silt-free stream bottoms, as too much silt can smother them. They do well in shaded stream banks with vegetation that can help regulate water temperature and provide dead leaves and plant material useful as food.
"These are filter feeders," says Wolf. They siphon nutrients via intake vents set amid an assortment of digestive and reproductive organs and muscles for opening and closing the shell, as well as two sets of teeth used to align the shells when closed. Heelsplitter larvae find and attach themselves to the gills of host fish by way of hooks at the end of their closed shells.
"They are active parasites at this stage of life," says Wolf, "using the tissue or blood supply of the host fish to receive nutrients. The heelsplitter is considered a host generalist," although, she adds, the species most often used are the bluehead chub, golden shiner and highfin shiner. "Over the past few years, we have utilized bluehead chub and white shiners for propagation efforts at our Orangeburg Mussel Conservation Center, part of the Orangeburg National Fish Hatchery, with great success."
Once attached to a host fish, the larvae develop for several more weeks, then detach and drop to the stream bottom. In the meantime, the transportation provided by the fish has classically helped heelsplitters create new populations up- or downstream. Whether there are enough mussels for that strategy to be helpful going forward remains an open question. A recovery plan, authored by John Fridell, formerly of the USFWS's Asheville, North Carolina, office, and approved in January of 1997, sounded an ominous note. "Lack of proper protection and management of these populations, particularly the populations in South Carolina," it said, "will preclude recovery of the Carolina heelsplitter and will ultimately lead to the species' extinction."
But there is work underway and cautious optimism on the part of Wolf and others.
"It is no longer the case that the heelsplitter is too far gone to help," Wolf says. She cites the Conservation Center work to restore degraded habitat and other recovery activities, including joint efforts with the SCDNR. "We are now firing on all cylinders by actively conserving and restoring habitat, as well as surveying, propagating and augmenting existing populations."
For Wolf, the cause remains personal.
"The first official heelsplitter survey I helped out with took place in Flat Creek in Lancaster County. The very first mussel I found and pulled up that day was a heelspslitter. Fast forward six years and we now have an active propagation effort established for the species. Guess which creek we returned to, to put heelsplitters back in the wild for the first time in South Carolina history - Flat Creek. The moment was, needless to say, a very powerful one for me."
And we as wildlife watchers can hope it bodes well for the future of this imperiled species.