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Aquatic Species of Concern

Primary Question (chapter 23): What are the history, status, and likely future of aquatic habitats and species in the South?

The South’s streams, riparian areas, and wetlands contain a great diversity of aquatic life (chapter 23). For example, 91 percent of the freshwater mussels described in the world are present in the South. Modification of aquatic and wetland habitats has greatly influenced this biota, and effects of past actions are in some cases particularly severe. For example, dam construction has irreversibly changed habitats for certain snails and freshwater mussels that depend on free-flowing water.

To enumerate and examine species of conservation concern, the databases of the State Natural Heritage agencies were used to list species by their global conservation rank. The global ranks reflect scarcity for the entire range of the species. These ranks include presumed extinct, possibly extinct, critically imperiled, imperiled, vulnerable, apparently secure, and secure. Species of conservation concern include those that are critically imperiled (extremely rare—observations include 5 or fewer locations or fewer than 1,000 animals—or otherwise vulnerable to extinction), imperiled (rare—observations in 6 to 20 locations or fewer than 2000 animals—or otherwise vulnerable to extinction), or vulnerable (21 to 100 locations or 3,000 to 10,000 animals or found only locally in a restricted area). We evaluated the status of the region’s aquatic species of concern (chapter 23) and found:

• Amphibians—Thirty-one amphibian species of concern, including 28 salamanders, 2 frogs, and 1 toad are located in the South. These rare amphibians are concentrated in three areas: the Southern Appalachians, the Florida Panhandle, and central Texas. Many species in the Appalachians are concentrated in national forests and national parks. In the Florida Panhandle, habitat is largely in private ownership (fig. 48).

• Mussels—The South contains the highest diversity of mussel species in the world; 91 percent of the world’s known species occur here, and almost 80 percent of them are endemic to single watersheds. The region has 191 mussel species of concern; 67 are critically imperiled. Among several key river basins, the Tennessee, Cumberland, and Mobile basins host particularly diverse populations of rare mussels (fig. 49). Because mussels are long-lived species (up to 100 years), population trends reflect habitat modifications that occurred decades earlier. Declines in mussels are most critically linked to channelization and damming of rivers and the associated modifications to streambeds, water flow, and sedimentation. Extirpation of fish species that serve as hosts to mussel glochidia (juvenile mussels) also contribute to mussel decline. The introductions of exotic species (Asian clams and zebra mussels) have also accelerated the decline of native mussels.

• Crayfish and other crustaceans—The South contains a broad diversity of crustacean species, including 159 species of concern and 60 that are critically imperiled. While they occur throughout the South, the area with largest concentration of crustacean species is the Florida Panhandle. Because the species are generally endemic to very small areas, modification of these habitats can have substantial impact on their viability. While crayfish are generally very resilient—able to withstand transitory habitat modifications—habitat destruction in small areas can eliminate entire populations.

• Fish—The South contains 165 fish species of concern in 14 different families, and their occurrence is widespread. With the exception of central Mississippi and southern Florida, rare fish are present throughout the South (fig. 50). Many of these species are narrowly endemic, especially the darters, minnows, topminnows, catfish, gambusia, and sculpins. Because of this high degree of endemism, a few events or even a single event can have substantial impact on species viability. Declines have been associated with a wide variety of factors, including habitat modification, pollution, sedimentation, damming, introduced species, and interruption of water flow.

• Snails—The South has 127 snail species of concern: 104 utilize stream habitat, 22 are found in springs and caves, and 1 is a lake snail. The snails found in springs and caves are narrow endemics concentrated most in Florida. They are especially susceptible to ground-water contamination and sedimentation. Eighty-nine of the 100 stream species are in the Tennessee and Mobile River Systems. Because they require free-flowing water, damming has had the greatest impact on these species. Remnant subpopulations are isolated, thereby limiting within-population genetic variability. Snails are also susceptible to pollution and to predation and competition from exotic species (e.g., zebra mussels).

• Insects—One hundred seventy-six insect species of concern—including 64 stoneflies, 60 caddisflies, 31 dragonflies, and 4 damselflies—are found in the South. Their nymphal stages require clean flowing water for effective feeding. Adults forage in adjacent terrestrial habitats. Declines have been strongly associated with dams, which reduce flow and allow for sedimentation of habitat. All of these species are vulnerable to further sedimentation and pesticide pollution.

• Reptiles—Nineteen species of concern, including one critically imperiled species, are found in the South. Many of these species are located in a large contiguous area stretching from central and southern Mississippi and Alabama to the Florida Panhandle. While these species are generally resilient, they are narrow endemics and so especially susceptible to local events. Specific threats include harvest for pets, indiscriminant killing, and damage to nests.