Aquatic Fauna in Peril: The Southeastern Perspective
Edited By George W. Benz And David E. Collins
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Aquatic Fauna in Peril: The Southeastern PerspectiveEdited By George W. Benz And David E. Collins |
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Aquatic mollusks in the southeastern United States reside in a wide variety of permanent and seasonal aquatic habitats, and the diversity of bivalves and gastropods in the Southeast is globally unparalleled. Aquatic mollusks are distributed throughout the many tributaries of major rivers in the Interior Basin that drain various physiographic provinces along the South Atlantic and Gulf Coasts. Rivers of the southern Interior Basin, and of the Coastal Plain, originate in or traverse through several physiographic provinces: Appalachian Highlands, Ridge and Valley, Blue Ridge, Piedmont Plateau, Cumberland Plateau, and Coastal Plain. Regional and historical differences in physiography, geology, water chemistry, and other stream characteristics have resulted in distinct faunal assemblages and considerable endemism within river basins. Heard (1970) attributed striking differences in the southeastern freshwater molluscan fauna to assemblages adapted to specific lotic conditions (small streams vs. large rivers) and to locales with differences in specific environmental conditions (substratum, food availability, etc.). Riverine ecosystems may account for the highest diversity of freshwater mollusks because they are more permanent in an evolutionary time scale than lakes or other freshwater environments. They also contain a greater heterogeneity of physico-chemical characteristics and biological niches for aquatic organisms to adapt to and evolve with — from small headwater streams with swift current and allochthonous energy contributions to large coastal plain rivers with slow flow and autochthonous production.
A plethora of natural and anthropogenic factors have influenced the current distribution of freshwater mollusk species. However, differentiating between these factors is difficult without sufficient historic surveys and collection records to support conclusions. Extensive biological inventories were never conducted in most Southeast aquatic ecosystems. Therefore, the degree of aquatic faunal losses is unknown (Schindler, 1989). Because freshwater mollusks have never been a faunal group of great interest to federal and state natural resource agencies, much historic knowledge is derived from the collections and writings of early naturalists who traveled the eastern United States, in search of new animals and environments. Unfortunately, the early taxonomy and systematics of freshwater mollusks were based principally on shell characteristics that vary within and between rivers. As a result, an abundance of nominal species was described in the 19th century (Rafinesque, 1820, 1831; Lea, 1834-1874). Only in the 20th century has a concerted effort been made to evaluate early descriptions, identify synonomies, and compile a more accurate list of resident mollusk species in the rivers of the United States. For purposes of this chapter, we adopt the nomenclature of Turgeon et al. (1988).
Species richness of freshwater mollusks in the United States consists of more than 850 species in three taxonomic groups (Table 1). Snails are the most diverse taxon, accounting for 60 percent of all mollusk species. When this species richness is assessed from a regional perspective, it is readily apparent that the "rain forest" of mollusk diversity is in the southeastern United States. Based on Turgeon et al. (1988) and taxonomic keys and distribution records, we calculate that 91 percent of the mussels, 53 percent of the fingernail clams, and 61 percent of the snails in the United States occur in one or more states of the Southeast (Table 1). It is important to acknowledge that new species of freshwater mollusks continue to be described (Thompson and Hershler, 1991; Bogan and Hoeh, 1994), because sampling in localized habitats and new genetic techniques provide more decisive data and tools to help indicate the phylogenies and origins of mollusks in the Southeast. These tallies of species richness, especially for the mussels and snails, will undoubtedly increase.
Table 1. Species richness of freshwater mollusks in the southeastern United States. |
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Taxonomic Group |
Number of U.S. Species |
Number of Species in Southeast 1 |
Mussels |
297 |
269 (91) |
Fingernail Clams |
38 |
20 (53) |
Snails |
516 |
313 (61) |
1 Percent of U.S. species in parentheses. |
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Much knowledge of affinities among mollusk assemblages in rivers is derived
from studies of freshwater mussels (Unionoidea). Unionids offer three advantages
for 
zoogeographic
study: they are relatively sedentary, reasonable numbers of species are readily
distinguishable, and generic affinities have been fairly well defined (Burch,
1973). The dispersal ability of mussels is restricted principally to the glochidial
stage and the mobility of their host fish species. Freshwater fishes are generally
confined to specific river drainages and can migrate between adjacent river
basins only after physiographic changes to the landscape, such as stream captures
or base leveling during glacial events. For these reasons, mussel distributions
seem to be excellent indicators of physiographic change between adjacent river
systems through geologic time. Molluscan faunal zones have been defined by their
distinctive mussel and snail assemblages — sharing various numbers of species
with other rivers according to drainage modification, isolation, confluence,
stream capture, and other phenomena from regional or global events such as glaciation
and sea level changes. The direct and indirect effects of these events on local
biota and ecology have shaped distinctive communities with traceable phylogenies.
For example, mussels have provided convincing evidence of major stream confluences
(van der Schalie, 1945). Historic connections between the Apalachicola and Savannah
rivers are suggested by their mollusk assemblages. Suffice it to say that lengthy
discussions of zoogeography and zonation of aquatic fauna in the Southeast have
been made possible by the distribution patterns of mollusks (van der Schalie
and van der Schalie, 1950; Johnson, 1970, 1980; Hocutt and Wiley, 1986).
Because few extensive or intensive historic surveys were conducted on southeastern freshwater mollusk taxa, except for perhaps freshwater mussels, it is not possible to document the many changes in diversity, abundance, and distribution that have occurred in the last 100 years. Therefore, we are unable to describe the extent of decline of many mollusk groups throughout the Southeast. Our approach here is to select river systems with historic and recent collection records to serve as case studies for mollusks, principally freshwater mussels and river snails. These are the most diverse families of mollusks in the Southeast, and they are suitable indicators of change to their communities and environments. Other families of bivalves (fingernail clams: Sphaeriidae) and gastropods (e.g., freshwater limpets: Ancylidae) have been too poorly surveyed or sampled to provide an assessment of species stability or decline. Hopefully the results of this paper will stimulate interest in determining the status of other families and genera of mollusks in this region. There is still much to be done in the taxonomy, biology, and ecology of freshwater mollusks so that appropriate conservation efforts can be directed to those taxa or habitats in need of protection or recovery.
Freshwater mussels of the families Unionidae and Margaritiferidae are the best studied group of freshwater mollusks in the United States, with adequate historic and recent collection records to document changes in distribution and abundance of many species. Of the 297 species and subspecies currently recognized (Turgeon et al., 1988), 269 species had historic ranges that overlapped the political boundaries of one or more states of the Southeast. Species richness varies among southeastern states, ranging from an historic high of 175 species in Alabama to 33 species in South Carolina (Figure 1). These totals were compiled principally during the early 20th century and have changed drastically during the last 70 years.
The Endangered Species Act of 1973 and subsequent amendments provided the legal means for recognition of rare mollusks that deserve federal protection. In June 1976, 23 species of freshwater mussels were designated as endangered. Because of internal priorities in the U.S. Fish and Wildlife Service and because of the overwhelming number of vertebrate and invertebrate species deserving of consideration under the Act, no additional species of mussels were listed until 1988 (Figure 2). Since then, a profound increase in listings has reflected the recognition of serious declines in freshwater bivalves by field biologists of the U.S. Fish and Wildlife Service, particularly in the Southeast. As of January 1995, 56 mussel species are federally listed as endangered or threatened in the United States. Except for the Curtis pearlymussel (Epioblasma florentina curtisi) in Missouri and the white catspaw (E. obliquata perobliqua) in Indiana, Michigan, and Ohio, the 53 other listed species were known historically from one or more states in the Southeast (Table 2). In addition to these protected species, federal biologists identified 51 candidate species of mussels awaiting evaluation for possible listing (Table 3), all of which occur in southeastern states. Thus, more than 34 percent of all mussel species nationwide are in varying degrees of rarity, and 98 percent of these rare species occur in the Southeast.
Table 2. Species of freshwater mussels and snails federally designated as endangered or threatened in the southeastern United States in 1994. |
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Scientific Name |
Common Name |
Historic Range |
Status |
Mussels: |
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dwarf wedgemussel |
CT, DC, DE, MA, MD, NC, NH, PA, VT, VA |
E |
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Ouachita rock pocketbook |
AR, OK |
E |
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fanshell |
AL, IL, IN, KY, OH, PA, TN, VA, WV |
E |
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dromedary pearlymussel |
AL, KY, TN, VA |
E |
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Tar spinymussel |
NC |
E |
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yellow blossom |
AL, TN |
E |
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tan riffleshell |
KY, TN, VA |
E |
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upland combshell |
AL, GA, TN |
E |
|
catspaw |
AL, IL, IN, KY, OH, TN |
E |
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southern acornshell |
AL, GA, TN |
E |
|
southern combshell |
AL, MS |
E |
|
green blossom |
TN, VA |
E |
|
northern riffleshell |
IL, IN, KY, MI, OH, PA, WV |
E |
|
tubercled blossom |
IL, IN, KY, TN, WV |
E |
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turgid blossom |
AL, TN |
E |
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shiny pigtoe |
AL, TN, VA |
E |
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fine-rayed pigtoe |
AL, TN, VA |
E |
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cracking pearlymussel |
AL, IL, IN, KY, OH, TN, VA |
E |
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pink mucket |
AL, IL, IN, KY, MO, OH, PA, TN, VA, WV |
E |
|
fine-lined pocketbook |
AL, GA |
E |
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orange-nacre mucket |
AL, MS |
T |
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Arkansas fatmucket |
AR |
T |
|
speckled pocketbook |
AR |
E |
|
Alabama lampmussel |
AL, TN |
E |
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Carolina heelsplitter |
NC, SC |
E |
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birdwing pearlymussel |
AL, TN, VA |
E |
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Louisiana pearlshell |
LA |
T |
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Alabama moccasinshell |
AL, GA, MS |
T |
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Coosa moccasinshell |
AL, GA, TN |
E |
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ring pink |
AL, IL, IN, KY, OH, PA, TN, WV |
E |
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little-wing pearlymussel |
AL, KY, NC, TN, VA |
E |
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white wartyback |
AL, IN, TN |
E |
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orange-foot pimpleback |
AL, IN, IA, KY, OH, PA, TN |
E |
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clubshell |
AL, IL, IN, KY, MI, OH, PA, TN, WV |
E |
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James spinymussel |
VA, WV |
E |
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black clubshell |
AL, MS |
E |
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southern clubshell |
AL, GA, MS, TN |
E |
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dark pigtoe |
AL |
E |
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southern pigtoe |
AL, GA, TN |
E |
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Cumberland pigtoe |
TN |
E |
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flat pigtoe |
AL, MS |
E |
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ovate clubshell |
AL, GA, MS, TN |
E |
|
rough pigtoe |
AL, IN, KY, TN, VA |
E |
|
heavy pigtoe |
AL, MS |
E |
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fat pocketbook |
AR, IN, MO, OH |
E |
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inflated heelsplitter |
AL, LA, MS |
T |
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triangular kidneyshell |
AL, GA, TN |
E |
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winged mapleleaf |
IA, IL, IN, KY, MN, MO, NE, OH, OK, TN, WV |
E |
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Cumberland monkeyface |
AL, TN, VA |
E |
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Appalachian monkeyface |
AL, TN, VA |
E |
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stirrupshell |
AL, MS |
E |
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pale lilliput |
AL, TN |
E |
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Cumberland bean |
KY, TN |
E |
Snails: |
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tulotoma snail |
AL |
E |
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Anthony's riversnail |
AL, TN |
E |
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royal marstonia |
TN |
E |
Table 3. Species of freshwater mussels on the federal candidate list in the southeastern United States in 1994.1 |
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Scientific Name |
Common Name |
State(s) of Occurrence |
Alasmidonta arcula (Lea, 1838) |
Altamaha arc-mussel |
GA |
A. atropurpurea (Rafinesque, 1831) |
Cumberland elktoe |
KY, TN |
A. raveneliana (Lea, 1834) |
Appalachian elktoe |
NC |
A. varicosa (Lamarck, 1819) |
brook floater |
GA, NC, SC, VA |
A. wrightiana (Walker, 1901) |
Florida arc-mussel |
FL |
Amblema neislerii (Lea, 1858) |
fat three-ridge |
FL, GA |
Anodontoides denigrata (Lea, 1852) |
Cumberland papershell |
KY, TN |
Cumberlandia monodonta (Say, 1829) |
spectaclecase |
AL, AR, KY, TN, VA |
Cyprogenia aberti (Conrad, 1850) |
western fanshell |
AR |
Elliptio sp. |
Waccamaw lance |
NC |
E. chipolaensis Walker, 1905 |
Chipola slabshell |
AL, FL |
E. judithae Clarke, 1986 |
Neuse slabshell |
NC |
E. lanceolata (Lea, 1828) |
yellow lance |
NC, VA |
E. marsupiobesa Fuller, 1972 |
Cape Fear spike |
NC |
E. monroensis (Lea, 1843) |
St. Johns elephantear |
FL |
E. nigella (Lea, 1852) |
winged spike |
AL, GA |
E. shepardiana (Lea, 1834) |
Altamaha lance |
GA |
E. spinosa (Lea, 1836) |
Altamaha spinymussel |
GA |
E. waccamawensis (Lea, 1863) |
Waccamaw spike |
NC |
E. waltoni (Wright, 1888) |
Florida lance |
FL |
Elliptoideus sloatianus (Lea, 1840) |
purple bankclimber |
AL, GA, FL |
Epioblasma brevidens (Lea, 1831) |
Cumberlandian combshell |
AL, KY, TN, VA |
E. capsaeformis (Lea, 1834) |
oyster mussel |
AL, KY, TN, VA |
E. triquetra (Rafinesque, 1820) |
snuffbox mussel |
AL, KY, MS, TN, VA |
Fusconaia escambia Clench and Turner, 1956 |
narrow pigtoe |
AL, FL |
F. masoni (Conrad, 1834) |
Atlantic pigtoe |
GA, NC, SC, VA |
Lampsilis australis Simpson, 1900 |
southern sandshell |
AL, FL |
L. binominata Simpson, 1900 |
lined pocketbook |
AL, GA |
L. cariosa (Say, 1817) |
yellow lampmussel |
GA, NC, SC, VA |
L. fullerkati Johnson, 1984 |
Waccamaw fatmucket |
NC |
L. rafinesqueana Frierson, 1927 |
Neosho mucket |
AR |
L. subangulata (Lea, 1840) |
shiny-rayed pocketbook |
AL, FL, GA |
Lasmigona sp. |
Barrens heelsplitter |
KY |
L. holstonia (Lea, 1838) |
Tennessee heelsplitter |
AL, GA, KY, TN, VA |
L. subviridis (Conrad, 1835) |
green floater |
NC, SC, VA |
Leptodea leptodon (Rafinesque, 1820) |
scaleshell |
AR, KY |
Lexingtonia dolabelloides (Lea, 1840) |
slabside pearlymussel |
AL, TN, VA |
Margaritifera marrianae Johnson, 1983 |
Alabama pearlshell |
AL |
Medionidus penicillatus (Lea, 1857) |
Gulf moccasinshell |
AL, FL, GA |
M. simpsonianus Walker, 1905 |
Ochlocknee moccasinshell |
FL |
M. walkeri (Wright, 1897) |
Suwanee moccasinshell |
FL |
Obovaria rotulata (Wright, 1899) |
round ebonyshell |
AL, FL |
Pleurobema oviforme (Conrad, 1894) |
Tennessee clubshell |
KY, TN, VA |
P. pyriforme (Lea, 1857) |
oval pigtoe |
AL, FL, GA |
P. rubellum (Conrad, 1834) |
Warrior pigtoe |
AL |
P. rubrum (Rafinesque, 1820) |
pink pigtoe |
AL, KY, MS, TN, VA |
P. strodeanum (Wright, 1898) |
fuzzy pigtoe |
AL, FL |
P. verum (Lea, 1860) |
true pigtoe |
AL |
Potamilus amphichaenus (Frierson, 1898) |
Texas heelsplitter |
LA |
Ptychobranchus jonesi (van der Schalie, 1934) |
southern kidneyshell |
AL, FL |
P. occidentalis (Conrad, 1836) |
Ouachita kidneyshell |
AR |
Quadrula cylindrica cylindrica (Say, 1817) |
rabbitsfoot |
AL, AR, KY, TN |
Q. c. strigillata (Wright, 1898) |
rough rabbitsfoot |
KY, TN, VA |
Quincuncina burkei Walker, 1922 |
tapered pigtoe |
AL, FL |
Simpsonaias ambigua (Say, 1825) |
salamander mussel |
AR, KY, TN |
Toxolasma lividus (Rafinesque, 1831) |
purple lilliput |
KY, TN |
T. pullus (Conrad, 1838) |
Savannah lilliput |
GA, NC, SC |
Villosa choctawensis Athearn, 1964 |
Choctaw bean |
AL, FL |
V. fabalis (Lea, 1831) |
rayed bean |
AL, TN, VA |
V. ortmanni (Walker, 1925) |
Kentucky creekshell |
KY |
V. perpurpurea (Lea, 1861) |
purple bean |
TN, VA |
1 Information from U.S. Federal Register 59(219):59008-59010; November 15, 1994. |
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A recent status review of the mussel fauna in the entire United States revealed significant nationwide declines (Williams et al., 1993). Many mussel species are more depleted than federal lists indicate. In the southeastern states, between 34 percent and 71 percent of the species or populations of species are imperiled, defined here to include endangered, threatened, or of special concern species (Table 4). In spite of the large differences in diversity of mussels among states, the decline of species is ubiquitous in coastal and in Interior Basin rivers. States in the Tennessee River Basin such as Alabama, Tennessee, and Virginia have the highest percentages of imperiled species, whereas coastal states with lower species richness have lower percentages of imperiled species. Best available data indicate that mussel species in the Tennessee River Basin, which includes portions of seven states in the Southeast, are in the most severe decline. Many of the extinct species occurred in the Tennessee and Cumberland rivers and in their major tributaries in Alabama, Tennessee, and Kentucky (Table 5). All 36 species that are presumed extinct occurred in the Southeast, and nearly 40 percent (14) of these were Pleurobema spp. endemic to the Mobile River Basin. As a group, the riffleshells (Epioblasma spp.) have suffered the highest level of extinctions, presumably because of their occurrence in the shoals of mid-size and large rivers that were destroyed by dams and dredging and their intolerance of degraded water quality (Ahlstedt, 1991a). This group of species is seemingly sensitive to physical or chemical changes in habitat suitability, and they are the first to disappear from rivers under anthropogenic disturbance.
Table 4. Status of freshwater mussels in the southeastern United States in 1994. |
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State |
Number of Species |
Number Extinct |
Number Endangered |
Number Threatened |
Number Special Concern |
Total Number Imperiled (Percent) |
AL |
175 |
28 |
51 |
20 |
37 |
136 (78) |
TN |
132 |
17 |
41 |
10 |
29 |
93 (70) |
KY |
102 |
12 |
22 |
7 |
19 |
60 (58) |
GA |
98 |
8 |
23 |
14 |
34 |
72 (73) |
MS |
84 |
0 |
9 |
10 |
21 |
40 (48) |
VA |
80 |
2 |
21 |
9 |
25 |
57 (71) |
AR |
70 |
1 |
6 |
9 |
13 |
29 (41) |
LA |
64 |
0 |
2 |
7 |
13 |
22 (34) |
FL |
51 |
1 |
5 |
10 |
13 |
29 (57) |
NC |
49 |
1 |
6 |
6 |
16 |
29 (59) |
SC |
33 |
1 |
2 |
5 |
10 |
18 (55) |
A
recent assessment of the aquatic mollusks in North Carolina typifies the extent
of decline in some populations (Scientific Council on Freshwaterand Terrestrial
Mollusks, 1990). Thirty-three (53 percent) of the freshwater mussels in the
state are threatened with extinction, and another 42 species of mollusks are
too poorly known to define their statuses. The collapse of mussel populations
in North Carolina is severe: 62 of 147 populations are reported to be in poor
or very poor condition, and only 19 populations are in very good condition (Rader,
1994). According to Alderman et al. (1992), only 51 of the 147 mussel populations
are likely to maintain viable populations over the next 30 years in North Carolina.
Causes for these declines include waste discharges, nonpoint-source pollution
(especially sediment), reduced instream flow, and competition from exotic species.
Table 5. Species of freshwater mussels in the United States presumed to be extinct. |
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Scientific Name |
Common Name 1 |
State(s) of Occurrence |
Alasmidonta maccordi Athearn, 1964 |
Coosa elktoe |
AL |
A. robusta Clarke, 1981 |
Carolina elktoe |
NC, SC |
A. wrightiana (Walker, 1901) |
Ochlocknee arc-mussel |
FL |
Elliptio nigella (Lea, 1852) |
winged spike |
AL, GA |
Epioblasma arcaeformis (Lea, 1831) |
sugar spoon |
AL, KY, TN |
E. biemarginata (Lea, 1857) |
angled riffleshell |
AL, KY, TN |
E. flexuosa (Rafinesque, 1820) |
leafshell |
AL, KY, TN |
E. f. florentina (Lea, 1857) |
yellow blossom |
AL, KY, TN |
E. haysiana (Lea, 1833) |
acornshell |
AL, KY, TN, VA |
E. lenior (Lea, 1843) |
narrow catspaw |
AL, TN |
E. lewisii (Walker, 1910) |
forkshell |
AL, KY, TN |
E. obliquata obliquata (Rafinesque, 1820) |
catspaw |
AL, KY, TN |
E. personata (Say, 1829) |
round combshell |
KY |
E. propinqua (Lea, 1857) |
Tennessee riffleshell |
AL, KY, TN |
E. sampsonii (Lea, 1861) |
wabash riffleshell |
KY |
E. stewardsoni (Lea, 1852) |
Cumberland leafshell |
AL, KY, TN |
E. torulosa gubernaculum (Reeve, 1865) |
green blossom |
TN, VA |
E. t. torulosa (Rafinesque, 1820) |
tubercled blossom |
AL, KY, TN |
E. turgidula (Lea, 1858) |
turgid blossom |
AL, AR, TN |
Lampsilis binominata Simpson, 1900 |
|
AL, GA |
Medionidus macglameriae
|
Tombigbee moccasinshell |
AL |
Pleurobema aldrichianum Goodrich, 1831 |
|
AL, GA |
P. altum (Conrad, 1854) |
highnut |
AL |
P. avellanum Simpson, 1900 |
hazel pigtoe |
AL |
P. chattanoogaense (Lea, 1858) |
painted clubshell |
AL, GA, TN |
P. flavidulum (Lea, 1831) |
yellow pigtoe |
AL |
P. hagleri Frierson, 1906 |
|
AL |
P. hanleyanum (Lea, 1852) |
Georgia pigtoe |
AL, GA, TN |
P. hartmanianum (Lea, 1860) |
|
AL, GA |
P. johannis (Lea, 1859) |
Alabama pigtoe |
AL |
P. murrayense (Lea, 1868) |
Coosa pigtoe |
AL, GA, TN |
P. nucleopsis (Conrad, 1849) |
longnut |
AL, GA |
P. rubellum (Conrad, 1834) |
Warrior pigtoe |
AL |
P. troschelianum (Lea, 1852) |
Alabama clubshell |
AL |
P. verum (Lea, 1860) |
true pigtoe |
AL |
Quadrula tuberosa (Lea, 1840) |
rough rockshell |
TN, VA |
1 Not all species have common names. |
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Table 6. Fingernail clams occurring in the southeastern United States. |
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Scientific Name |
Common Name |
Sphaerium fabale (Prime, 1852) |
river fingernail clam |
S. occidentale (Lewis, 1856) |
Herrington fingernail clam |
S. striatinum (Lamarck, 1818) |
striated fingernail clam |
S. simile (Say, 1817) |
grooved fingernail clam |
Musculium lacustre (Müller, 1774) |
lake fingernail clam |
M. partumeium (Say, 1822) |
swamp fingernail clam |
M. securis (Prime, 1852) |
pond fingernail clam |
M. transversum (Say, 1829) |
long fingernail clam |
Eupera cubensis (Prime, 1865) |
mottled fingernail clam |
Pisidium dubium (Say, 1817) |
greater eastern peaclam |
P. adamsi Stimpson, 1851 |
Adam peaclam |
P. casertanum (Poli, 1791) |
ubiquitous peaclam |
P. compressum Prime, 1852 |
ridged-back peaclam |
P. equilaterale Prime, 1852 |
round peaclam |
P. fallax Sterki, 1895 |
river peaclam |
P. nitidum Jenyns, 1832 |
shiny peaclam |
P. variable Prime, 1852 |
triangular peaclam |
P. walkeri Sterki, 1895 |
Walker peaclam |
P. punctatum Sterki, 1895 |
perforated peaclam |
P. punctiferum (Guppy, 1867) |
striate peaclam |
The current status and prognosis for the Southeast region’s mussel fauna is grim. Of the 269 species in the Southeast, 13 percent are presumed extinct, 28 percent are endangered, 14 percent are threatened, 18 percent are of special concern, and only 25 percent are considered stable at this time.
Exploitation of the mussels by humans for food, tools, and ornaments and the deposition of shells in midden piles have provided an excellent archaeological record of species composition during the past 10,000 years. The presence of mussels at archaeological sites has been invaluable in reconstructing prehistoric faunal assemblages and ecological conditions in early times (Bogan, 1990). For example, as judged by the species in shell middens, at least 91 species of mussels occurred in the mainstem Tennessee River during pre-colonial times. That original diversity profoundly changed in this century from human perturbations to the mainstem river. A plethora of dams and degradation of water quality produced irreconcilable changes to the river and its fauna. Results of surveys during the last ten years indicated that only 49 mussel species remain, of which 28 are reproducing and 21 likely are not (Figure 3). Most species with healthy populations were able to tolerate impounded waters and have increased in abundance above pre-impoundment population levels.
The fingernail clams (Sphaeriidae) are small bivalves that live in lotic, lentic, and ephemeral habitats throughout the United States. Of the 38 recognized species (Burch, 1975), about 20 species have ranges that extend into the southeastern states (Table 6). Members of this family are highly adaptable and exhibit an array of species-specific phenotypes to accommodate a variety of abiotic and biotic factors found in aquatic habitats. Some species inhabit stress-prone habitats such as ephemeral ponds and small streams, whereas others seemingly do well in profundal zones of lakes and reservoirs subject to hypoxia.
Fingernail clams, the smallest of freshwater bivalves, release the largest young. A combination of r-selected traits (short life span, early maturity, small size) and k-selected traits (ovoviviparity, low fecundity, large young) seemingly promotes fitness and survival of species that are subjected to periodic stress. Several species prefer coldwater habitats and are restricted to northern climates, whereas species in the Southeast are eurythermal and widespread. Therefore, except for three species of fingernail clams considered to be rare in the Pacific Northwest, none are imperiled in the Southeast. Comprehensive distributional or status reviews of sphaeriids in the United States have not been conducted principally because of the small size, difficulty of identification, and low physical and ecological profile of these clams. More extensive and intensive sampling of permanent and vernal habitats is needed before the occurrence, diversity, and stability of fingernail clam species in the Southeast can be described.
The freshwater gastropod fauna of North America is classified within 14 families and is represented by 516 species (Table 1). Diversity in the southeastern United States consists of 313 species or 61 percent of the native North American freshwater gastropod fauna. Freshwater gastropod diversity was greatest in the Mobile River Basin (118 species), and in the Tennessee River Basin (96 species; Table 7). The Coosa River drainage of the Mobile River Basin was home to four endemic genera (Hydrobiidae: Clappia; Pleuroceridae: Gyrotoma; Planorbidae: Amphigyra, Neoplanorbis). During the past 160 years, the aquatic gastropod fauna of the southeastern United States has been extensively described by Lea (1834-1874) and Goodrich (e.g., Goodrich, 1922, 1924, 1936, 1944a, 1944b), and summarized by Tryon (1873) and Burch (1989). The Hydrobiidae and the Pleuroceridae reached their greatest species richness in rivers of the Southeast. In spite of this great diversity, the ecology and life history of these animals are poorly understood. The freshwater periwinkles (Pleuroceridae) are relatively large snails that live on rocks, cobbles, and bedrock in riffles and shoals and are readily identified by shell characters. Conversely, the hydrobes (Hydrobiidae) are small (<8mm, = less than 0.3 inches) snails that reside in an array of freshwater habitats, from small seeps to large rivers, and typically require anatomical dissection for species identification.
Attention to the status of aquatic mollusk populations was uncommon. Ortmann (1909, 1918) recognized the effects of pollution, acid mine drainage, and dams on the native aquatic fauna. However, that attention was not focused on the decline and disappearance of the aquatic gastropod fauna of the Southeast until the publications of Athearn (1970), Stansbery (1971), Stein (1976) and more recently Bogan and Parmalee (1983), Palmer (1986), and Ahlstedt (1991b). Even now, the life history and ecology of most snail species is poorly understood, and the status of southeastern drainage faunas is virtually unknown. Based primarily on the papers cited above, Turgeon et al. (1988) assembled a list of 23 aquatic gastropods presumed to be extinct in the United States, all of which were endemic to the Mobile River Basin. With 118 species, this basin contained the most diverse aquatic gastropod fauna in the Southeast, and perhaps in the world (Table 7).
Table 7. Summary of the freshwater gastropod fauna in four major river systems in the southeastern United States. |
||||
Taxon |
Cumberland River Basin |
Tennessee River Basin |
Mobile River Basin |
Apalachicola River Basin |
Family: |
||||
|
0 |
0 |
1 |
1 |
|
1 |
1 |
1 |
1 |
|
0 |
0 |
0 |
1 |
|
1 |
4 |
4 |
3 |
|
2 |
20 |
18 |
5 |
|
2 |
3 |
1 |
1 |
|
14 |
50 |
76 |
11 |
|
2 |
2 |
2 |
2 |
|
5 |
5 |
2 |
2 |
|
5 |
6 |
9 |
5 |
|
3 |
7 |
4 |
4 |
Total Species |
35 |
96 |
118 |
36 |
Endangered Species |
0 |
0 |
1 |
0 |
Candidate Species |
8 |
35 |
70 |
3 |
Extinct Species |
0? |
0? |
26 |
0? |
Freshwater gastropods also have been neglected, relative to freshwater bivalves, as candidates for federal protection; only three freshwater gastropods are listed as endangered in the Southeast: Tulotoma magnifica, Athearnia anthonyi, and Pyrgulopsis ogmorphaphe. The tulotoma snail, which is endemic to the Mobile Basin, was presumed extinct until Hershler et al. (1990) discovered several extant populations. As of November 1994, roughly 210 species of 11 families of freshwater gastropods are on the federal list of candidate species. Of these candidate species, 144 (69 percent) occur in the Southeast (Table 8). Taxa from the Southeast account for most of the freshwater prosobranchs and about half of the freshwater pulmonate taxa on the candidate list. Two families (Hydrobiidae, Pleuroceridae) have the greatest number of candidate gastropod taxa.
Table 8. Species of freshwater gastropods on the federal candidate list in the southeastern United States, in 1994. 1 |
||
Taxon |
Common Name 2 |
State(s) of Occurrence |
Prosobranchia (135 Species): |
||
Viviparidae (2 species): |
||
|
cylindrical lioplax |
AL, GA, LA |
|
slender campeloma |
AL |
Hydrobiidae (50 species): |
||
|
|
AL |
|
Blue Spring hydrobe |
FL |
|
Wekiwa hydrobe |
FL |
|
dense hydrobe |
FL |
|
Fenney Spring hydrobe |
FL |
|
Crystal siltsnail |
FL |
|
Ichetucknee siltsnail |
FL |
|
Enterprise siltsnail |
FL |
|
pygmy siltsnail |
FL |
|
ponderous siltsnail |
FL |
|
Seminole siltsnail |
FL |
|
Wekiwa siltsnail |
FL |
|
Cahaba pebblesnail |
AL |
|
umbilicate pebblesnail |
AL |
|
flat pebblesnail |
AL |
|
Briley Creek pyrg |
AL |
|
Spring Creek pyrg |
AL |
|
Flint River pyrg |
AL |
|
Ocmulgee marstonia |
GA |
|
beaver pond marstonia |
GA |
|
olive marstonia |
AL |
|
royal marstonia |
TN |
|
Ozark pyrg |
AR |
|
armored marstonia |
AL |
|
Ouachita pebblesnail |
AR |
|
golden pebblesnail |
AL |
|
anglar pebblesnail |
AL |
|
knotty pebblesnail |
AL |
|
Coosa pebblesnail |
AL |
|
thick-lipped pebblesnail |
AR |
|
stocky pebblesnail |
AL |
|
Tennessee pebblesnail |
AL |
|
hidden pebblesnail |
AL |
|
ovate pebblesnail |
AL |
|
fluted pebblesnail |
AL |
|
granite pebblesnail |
AL |
|
atlas pebblesnail |
AL |
|
dwarf pebblesnail |
AL |
|
moon pebblesnail |
AL |
|
sparrow pebblesnail |
TN |
|
Tallapoosa pebblesnail |
AL |
|
pygmy pebblesnail |
AL |
|
quadrate pebblesnail |
AL |
|
mud pebblesnail |
AL |
|
rolling pebblesnail |
AL |
|
Savannah pebblesnail |
GA |
|
opaque pebblesnail |
AL, TN |
|
panhandle pebblesnail |
NC, VA |
|
channeled pebblesnail |
AR |
|
sculpin snail |
AL |
Pleuroceridae (83 species): |
||
|
Anthony's riversnail |
AL, GA, TN |
|
acute elimia |
AL, TN |
|
mud elimia |
FL |
|
black-crest elimia |
FL |
|
ample elimia |
AL |
|
Lily Shoals elimia |
AL |
|
coal elimia |
TN |
|
walnut elimia |
AL |
|
flaxen elimia |
AL |
|
short-spire elimia |
AL |
|
Cahaba elimia |
AL |
|
spindle elimia |
AL |
|
lacy elimia |
AL |
|
banded elimia |
AL |
|
fusiform elimia |
AL |
|
coldwater elimia |
AL |
|
high-spired elimia |
AL |
|
silt elimia |
AL |
|
gladiator elimia |
AL |
|
constricted elimia |
AL |
|
knotty elimia |
NC, TN |
|
slowwater elimia |
AL |
|
hearty elimia |
AL |
|
ribbed elimia |
AL |
|
round-ribbed elimia |
AL |
|
caper elimia |
AL |
|
engraved elimia |
AL |
|
rough-lined elimia |
AL |
|
nymph elimia |
AL |
|
pupa elimia |
AL |
|
spring elimia |
AL |
|
pygmy elimia |
AL |
|
compact elimia |
AL |
|
brook elimia |
TN |
|
elegant elimia |
TN |
|
mossy elimia |
TN |
|
cobble elimia |
AL |
|
puzzle elimia |
AL |
|
squat elimia |
AL |
|
excised slitshell |
AL |
|
striate slitshell |
AL |
|
pagoda slitshell |
AL |
|
ribbed slitshell |
AL |
|
pyramid slitshell |
AL |
|
round slitshell |
AL |
|
spiny riversnail |
AL, TN, VA |
|
round rocksnail |
AL |
|
agate rocksnail |
AL |
|
oblong rocksnail |
AL |
|
boulder snail |
AL, GA, TN |
|
interrupted rocksnail |
AL |
|
maiden rocksnail |
AL |
|
rotund rocksnail |
AL |
|
lyrate rocksnail |
AL |
|
black mudalia |
AL |
|
knob mudalia |
AL |
|
bigmouth rocksnail |
AL |
|
spotted rocksnail |
AL |
|
plicate rocksnail |
AL |
|
onyx rocksnail |
AL, TN, VA |
|
Coosa rocksnail |
AL |
|
painted rocksnail |
AL |
|
smooth rocksnail |
AL, TN, NC |
|
stripped rocksnail |
AL |
|
armored rocksnail |
AL, IN, KY, TN |
|
knobby rocksnail |
AL |
|
helmet rocksnail |
TN |
|
ornate rocksnail |
AL, KY, TN |
|
rugose rocksnail |
TN |
|
warty rocksnail |
AL, TN |
|
muddy rocksnail |
AL, TN |
|
varicose rocksnail |
AL, KY, TN |
|
rugged hornsnail |
AL, AR, KY, TN |
|
ringed hornsnail |
AL |
|
spiral hornsnail |
AL |
|
corpulent hornsnail |
AL, TN |
|
shortspire hornsnail |
AL, TN |
|
rough hornsnail |
AL, GA |
|
broken hornsnail |
AL |
|
skirted hornsnail |
AL, GA |
|
upland hornsnail |
AL, GA |
|
|
GA |
|
telescope hornsnail |
AL, TN |
Pulmonata (9 Species): |
||
|
||
Ancylidae (3 species): |
||
|
hood ancylid |
AL, FL |
|
domed ancylid |
AL |
|
wicker ancylid |
AL |
Planorbidae (6 species): |
||
|
shoal sprite |
AL |
|
|
AL |
|
|
AL |
|
|
AL |
|
|
AL |
|
magnificent rams-horn |
NC |
Total Aquatic Gastropods: 144 species |
||
1 Information from U.S.Federal Register 59(219):59000-59008; November 15, 1994. |
||
2 Not all species have common names. |
||
Of the aquatic gastropod fauna of four major river basins in the Southeast, the Mobile River Basin had the greatest original diversity but also suffered the greatest destruction and impairment of this fauna. This basin has one endangered species, 70 candidate taxa, and 26 presumed extinct taxa (Table 9). The Mobile fauna has suffered from the effects of damming of the major rivers, sedimentation from poor forestry and farming practices, pollution from industry, and the degradation of water quality as water passes through numerous water treatment facilities. The loss of species richness of the various drainages of the Mobile River Basin ranges from 33 to 84 percent (Table 9). In 1990, the U. S. Fish and Wildlife Service encouraged and supported studies to determine the range distribution and status of this remarkable fauna. Based on results of recent aquatic gastropod surveys by Bogan and Pierson (1993a, 1993b) and U.S. Fish and Wildlife Service personnel, we present a list of freshwater gastropods presumed to be extinct (Table 10). Losses in the Coosa River Basin are most severe. Four genera, with 13 species endemic to the Coosa River drainage, are presumed extinct (Clappia, Gyrotoma, Amphigyra, and Neoplanorbis). Most taxa resided in the main channel of the Coosa River. For example, the extinction of Gyrotoma probably occurred in the mid-1960s with the filling of Logan Martin Reservoir. The last living specimens were collected as the backwaters of the reservoir flooded the rocky shoals occupied by these species (H. Athearn, private museum, Cleveland, Tennessee, pers. comm.). When the series of dams on the Coosa River raised the water over the free-flowing shoals and covered them with silt, most of the fauna probably became extinct.
Table 9. Summary of the aquatic gastropod fauna in the Mobile River Basin. 1 |
|||||||
Taxon |
Alabama River |
Tombigbee River Drainage |
Black Warrior River Drainage |
Cahaba River Drainage |
Coosa River Drainage |
Talapoosa River Drainage |
Mobile River Basin Total |
Gastropod Families: |
|||||||
|
1 |
0 |
0 |
0 |
0 |
0 |
1 |
|
U |
U |
U |
U |
U |
U |
1 |
|
5 |
2 |
0 |
2 |
3 |
1 |
4 |
|
1 |
U |
1 |
3 |
12 |
2 |
18 |
|
U |
U |
U |
U |
U |
U |
1 |
|
7 |
2 |
11 |
22 |
55 |
1 |
76 |
|
2 |
2 |
2 |
2 |
2 |
2 |
2 |
|
2 |
2 |
2 |
2 |
2 |
2 |
2 |
|
U |
0 |
0 |
0 |
6 |
0 |
9 |
|
1 |
U |
1 |
1 |
2 |
0 |
4 |
Approximate total of historic gastropod species diversity |
19 |
8 |
17 |
36 |
82 |
8 |
118 |
Approximate number of collections |
150 |
50 |
100 |
160 |
324 |
16 |
800 |
Number of species found in recent surveys |
3 |
3 |
7 |
24 |
30 |
4 |
80 |
Federally listed endangered species |
1 |
0 |
0 |
0 |
1 |
0 |
1 |
Federal candidate species |
4 |
1 |
6 |
16 |
43 |
2 |
70 |
Number species presumed extinct |
U | ||||||