Aquatic Critters
October 11, 2014. Friends of Congaree Swamp is hosting an “aquatic critters appreciation hike” this morning. Department of Natural Resource fisheries biologist Jim Bulak and his assistants are providing a hands-on demonstration about the aquatic fauna of the park, a fauna that is mostly unseen and under-appreciated by the general public.
We are surveying two different water habitats, a flow-through, “lotic” system in the form of Cedar Creek, and a stagnant, “lentic” water body in the form of a back slough just on the other side of the bank from Cedar Creek. Jim is using an electro-shocker, a long-proven and efficient way to sample aquatic fauna by the use of an electrically-charged wand that delivers a mild jolt of electricity that stuns fish and other aquatic life, bringing them to the surface for capture and identification, after which they are released.
I am part of a crew sampling the stagnant back slough using dip nets, strainers and seines. Many of the sloughs are either dry or almost dry this time of year, but the rising waters we had on September 16 flooded many sloughs, including this one, and “re-charged” them with new inputs of aquatic life.
The bottom of the shallow slough consists of soft, gray mud as well as decomposing leaves, tupelo fruits, twigs and other detritus. Once disturbed, the bottom ooze gives off that characteristic swamp smell of anaerobic decomposition. After hauling a net full of mud and debris to the shore, we sort through it with our hands, which soon attain the smell that only a good hand-washing eliminates (it is not a bad smell but a pungent, earthy one that leaves an indelible mark on the olfactory senses). Our crew finds a few small crayfish and whirligig beetles. Later hauls produce water boatmen or back swimmers with large, oar-like appendages, diving beetles (at least two species), and a single, tiny minnow. All in all our sampling is rather sparse this morning, especially compared to June, when I was seeing lots of crayfish, minnows, and aquatic insects. But back then the sloughs had a good bit less water and its inhabitants were more concentrated.
Water boatman. Photo by John Grego
The electro-shockers on Cedar Creek are having better luck and have a cooler of water full of samples – mostly small fish but three specimens that really catch my eye – aquatic salamanders four-to-six inches long known as dwarf waterdogs, Necturus punctatus (and related to that other “canid” aquatic salamander, the mudpuppy). This interesting and relatively little known amphibian has a restricted range of only four southeastern states: Virginia, North Carolina, South Carolina, and Georgia. The heart of its range is the two Carolinas, where they are found in small coastal streams with abundant leaf litter, logs, stumps and other bottom debris. Like all salamanders, dwarf waterdogs are carnivorous, feeding on earthworms, snails, aquatic insects, crustaceans such as small crayfish, and even other salamanders. On the other hand a waterdog is no doubt a tasty meal for a largemouth bass, which probably accounts for the salamander’s preference for streams with lots of debris to serve as hiding places. It was first described to science in 1850 by Charleston physician, mathematician, and renaissance naturalist Lewis R. Gibbes from specimens obtained in rice field ditches on the South Santee River.
Another interesting specimen is an insect resembling the familiar “walking stick” of gardens and yards. A common name in fact is “water stick” or “needle bug,” but it usually goes by the name water scorpion. Our guy, a member of the true bug order Hemiptera, genus Ranatra, is black, very slender, and about three inches long. Although completely unrelated to true scorpions, the water scorpion is an aggressive aquatic predator that uses its long front legs to nab other aquatic insects and even tadpoles and small fish. They can also inflict a painful bite to a curious human handling them.
Water scorpion. Photo by John Grego.
Most of the specimens in the cooler of water are centrarchids, members of the sunfish family that include bluegill bream, crappie, and largemouth bass. There are several small bluegills, a red breast, pumpkinseed, and one flier, a small sunfish able to tolerate low oxygen conditions which allows it to survive in swampy backwaters and other sluggish aquatic habitats. There is also a madtom, a small, inconspicuous catfish found in a variety of aquatic habitats throughout the Carolinas and Virginia.
Swampfish. Photo by John Grego.
I have to leave early and find out later the group made some nice finds when they surveyed a small stream winding through the muck swamp on the north side of Cedar Creek. Samples here included a few redfin pickerel, a tessellated darter, several banded pygmy sunfish, and a single swampfish, Chologaster cornuta. The latter is a small, less-than-three-inch member of the cavefish family. Of the six species in this interesting family, four have no eyes, although the swampfish has tiny but functioning eyes. It also has an interesting developmental pattern whereby the anus migrates forward to the underside of its head.
The banded pygmy sunfish, Elassoma zonatum, is a diminutive (less-than-two-inches long), attractive centrarchid found in coastal blackwater streams and swamps. Although fairly common, this species is not known to most fishermen or the general public because of its size, inconspicuousness, and secretive habits.
Banded pygmy sunfish. Photo by John Grego.
From 1999 through 2002, the South Carolina Department of Natural Resources, working in conjunction with the National Park Service, conducted a four-year survey of the park’s fish community. This time period also happened to correspond with a severe drought in which the park rarely flooded. Over 10,000 fish, representing fifty-six species from thirty-three locations within the park, were collected and identified using electrofishing. Twenty-four of these species were new to the park. The survey also found three distinct fish-community habitat types within the park: backwater sloughs, guts, and other stagnant waters; deeper, flowing streams and channels; and floodplain waters adjacent to the northern bluffs.
I like to think of hardwood floodplains and their adjoining rivers as “fish factories” that produce prolific amounts of fish biomass. The abundance of aquatic habitats and rich resources serve as feeding, spawning, and nursery grounds for a large number of commercially- and recreationally-valuable species. The famous spawning runs of herring and shad end at bottomland sloughs and lakes where the eggs are laid in shallow water, sink, and adhere to various substrates on the bottom. Fish production in bottomlands has been estimated to vary from two hundred to more than one thousand pounds per acre.
Two weeks after our water sampling, The State newspaper released an article about water pollution in the park, based on samples taken in 2013 by the United States Geological Survey, working in conjunction with the Park Service. The samples, taken from both Cedar Creek and the Congaree River, showed higher levels of fecal coliform bacteria, probably from leaking septic tanks and failing wastewater treatment plants, as well as pesticide and herbicide run-off from farming activities. But what really caught the eye of many was the presence of prescription drugs in the water samples, including diabetes medication, mood stabilizers, and synthetic estrogen associated with birth-control pills. The latter is well-known for a phenomenon known as fish feminization and has become a growing concern across the country. Synthetic estrogens, along with certain industrial chemicals and herbicides released into our waterways, have been shown in some cases to be endocrine disruptors and to affect male fish by giving them female characteristics such as having eggs in their testes and producing female egg-yolk proteins. This in turn can led to reduced fertility by lowering sperm production and eventually lead to a decline in fish populations.
Endocrine disruptors have also affected other aquatic life, including frogs. Studies have documented male tadpoles turning into female frogs; frogs with reduced testosterone levels, impaired testes development, extra testes, and sometimes male frogs even having ovaries.
The irony in all this is that Cedar Creek was designated in 2007 as South Carolina’s only Outstanding National Resource Water, but by early 2014 it was listed as “impaired” by the South Carolina Department of Health and Environmental Control due to high fecal coliform bacteria counts.
Water pollution within Congaree National Park illustrates how nearly all parks and wild areas are like “islands,” essentially surrounded and affected by outside land uses. But unlike most, the Congaree is also an open ecosystem, and its “flow-through” floodplain makes it especially vulnerable to external events many miles upstream. As Frank Henning, former Director of Congaree’s Old-Growth Bottomland Hardwood Forest Research and Education Center, notes, water pollution is not a “problem that can be fixed within the park.”
