Characterization of the Ashepoo-Combahee-Edisto (ACE) Basin, South Carolina
Reptiles and amphibians (i.e., herpetofauna) occur in every habitat in the ACE Basin. Herpetofaunal communities are extensive and active throughout the year along the South Carolina coast because of its warm, humid climate. The composition of herpetofauna communities is primarily controlled by water regimes, salinity of the water, and structure of the vegetative community (Sandifer et al. 1980). Species such as the American alligator, the cottonmouth, and the southern toad are examples of species that inhabit a wide range of areas and are important members of the herpetofaunal community in many of the ACE Basin habitats. Other species, such as salamanders or certain treefrogs, may have a very restricted range of habitats because they cannot withstand exposure to saltwater, are very sensitive to dry conditions, or require ephemeral wetland habitats.
Research on herpetofauna of the ACE Basin is scarce. Because population abundance for reptiles and amphibians is difficult to estimate, such data does not exist for the ACE Basin; however, surveys from similar habitats in other areas can provide useful information to estimate the species potentially inhabiting the Basin. Approximately 110 species of herpetofauna have been documented or are expected to occur in the ACE Basin. Of these, there are 36 species of snakes, 18 species of turtles, 12 species of lizards including one introduced species, 20 species of frogs, 4 species of toads, 19 species of salamanders, newts and other amphibians, and 1 alligator species.
Because vegetative communities and herpetofauna are dependent on water conditions, many herpetofaunal communities are associated with particular plant communities and hydrologic conditions. Reptiles occurring in the coastal marine habitat, those areas just seaward of the ACE Basin, include the green, Kemps Ridley, loggerhead, hawksbill, and the occasional leatherback. Most of these are considered transients in South Carolina waters. The loggerhead is the only species that is regularly seen in the estuarine portions of the ACE Basin and also nests on the beaches of the barrier islands.
When compared to adjacent mainland areas, ACE Basin barrier islands (Edisto Beach, Otter Island, Deveaux bank, and Hunting Island) may have a lower abundance and diversity of species (Gibbons and Coker 1978). Only those reptiles and amphibians that can withstand the dry conditions in the dune and shrub habitats such as the six-lined race runner can be regularly found. Other species such as the island glass lizard (state species of concern), eastern glass lizard, eastern coachwhip, and eastern diamondback rattlesnake are seen occasionally (Gibbons and Harrison 1981). The diversity of reptile species that inhabit the maritime forest habitat is higher than dry dune and shrub environments because of the presence of moist habitats, intermittent or permanent water sources, and cover in the form of leaf litter, vegetation, and rotting logs that provide a variety of microhabitats for herpetofauna to utilize (Gibbons and Coker 1978; Sandifer et al. 1980). Species common to these barrier island forests are green treefrogs, Carolina anole, ground skinks, broadhead skinks, rat snakes, and eastern diamondback rattlesnakes. Other less frequently found species include squirrel treefrogs, southern leopard frogs, rough green snakes, southeastern crowned snakes, and cottonmouth snakes.
Because of the difficult conditions found in open water estuarine and salt marsh habitats, there are few species that utilize these habitats. The Carolina diamondback terrapin is the only species that is a resident. They are found in the tidal creeks of the salt marsh where they live and feed. The loggerhead is principally a marine species, but is also frequently seen in the rivers, generally feeding on crustaceans, jellyfish, and fishes. They are seasonal transients, moving south during the winter to find warmer waters. Alligators are known to feed in estuarine waters and may spend time in waters that are between 10 and 20 parts per thousand, but rarely stay in these areas for long periods. Similar to open water estuarine areas, estuarine impoundments are generally saline and have a limited number of herpetofauna. Diamondback terrapins, alligators, and occasionally cottonmouths are found. It is in oligohaline habitats, where the salinity is below 5 parts per thousand (ppt), that the diversity of species begins to increase (Sandifer et al. 1980).
In the tidal freshwater habitats, the number of species of reptiles increases from the numbers in estuarine areas, and many of the species found in the riverine system are also in tidal marshes and impoundments. Species found in freshwaters of the ACE Basin include a number of snakes such as the cottonmouth, redbelly water snake, banded water snake, and brown water snake as well as others. The American alligator and a number turtles including the Florida cooter, snapping turtle, river cooter, spiny softshell, and yellowbelly slider are found in riverine systems. These habitats are prime areas for the American alligator. The variety of habitats in forested wetlands may support more than 30 herpetofauna species. The anurans (frogs and toads) are the most abundant group in these habitats. Turtles are also an abundant group, with approximately seven species potentially occurring in tidal forested habitats.
Nontidal forested wetlands may go through periods of low water levels, restricting the number of species that are dependent on permanent water sources. Thus, while the herpetofauna of these regions are similar to tidal forested wetlands, some species are not found as regularly. A few species are found in nontidal wetlands that are not found frequently in tidal wetlands. These include the carpenter frog, little grass frog, the many-lined salamander, the three-lined salamander, and the oak toad. Some lizards and snakes that are more frequent in nontidal versus tidal forested wetlands because of the drier conditions are the eastern and slender glass lizards, black swamp snake, timber rattlesnake, and the southeastern crowned snake.
The diversity of habitats in upland hardwood and pine flatwood communities can result in a wide variety of herpetofauna. The species that occur in upland habitats in the ACE Basin are dependent on the history of rain in the previous months. Bullfrogs may by common during wet periods while lizards and pine woods treefrogs may be more common during dry periods. Snakes, with their armored scales, tend to dominate in the mostly dry habitat of the upland pine flatwood community. The dominant species include the corn snake, eastern diamondback rattlesnake, black racer, eastern garter snake, and pine snake. The pine woods treefrog is found in these habitats. The upland hardwood forest habitat tends not to be as dry as pine flatwoods and supports additional species of salamanders including the spotted salamander, marbled salamander, and the mole salamander as well as others. The copperhead and cottonmouth snakes are present in this habitat.
Reptiles and amphibians play an important role in the ACE Basin as predators that serve to control the populations of various prey species such as other reptiles and birds, and small mammals such as squirrels, rats, and mice. They are also important as prey species for birds, mammals, and other reptiles and amphibians and can make up most of the vertebrate biomass in some habitats (Burton and Likens 1975). Because of their habitat requirements, especially the amphibians, changes in the diversity of the reptile community may indicate changes in the habitats on which they are dependent and therefore may serve as indicators of environmental change or degradation (Pechmann et al. 1991; Blaustein et al. 1994; Fontenot et al. 1996).