PURPLE BANKCLIMBER

Elliptoideus sloatianus

SPECIES CODE: F02E I01

STATUS: On March 16, 1998, the purple bankclimber was designated as Threatened throughout its range (USFWS 1998). A recovery plan addressing the purple bankclimber was finalized on October 1, 2003 (USFWS 2003).

SPECIES DESCRIPTION: The purple bankclimber is a very large, heavy‑shelled, strongly sculptured mussel reaching lengths of 20.5 cm (8.0 in). A well-developed posterior ridge extends from the umbo to the posterior ventral margin of the shell. The posterior slope and the disk just anterior to the posterior ridge are sculptured by several irregular plications that vary greatly in development. The umbos are low, extending just above the dorsal margin of the shell. No sexual dimorphism is displayed in purple bankclimber shell characters. Internally, there is one pseudocardinal tooth in the right valve and two in the left valve. The lateral teeth are very thick and slightly curved, with one in the right valve and two in the left valve. Nacre color is whitish near the center of the shell becoming deep purple towards the margin, and very iridescent posteriorly. Fuller and Bereza (1973) described aspects of its soft anatomy, and characterized Elliptoideus as being an “extremely primitive” genus. The Service currently follows Turgeon et al (1998) and recognizes the purple bankclimber as Elliptoideus sloatianus with the following names considered synonyms: Unio atromarginatus Lea, 1840, Unio aratus Conrad, 1849, and Unio plectophorus Conrad, 1850.

Like other freshwater mussels, adults are filter-feeders, orienting themselves in the substrate to facilitate siphoning of the water column for oxygen and food (Kraemer 1979). Mussels have been reported to consume detritus, diatoms, phytoplankton, zooplankton, and other microorganisms (Coker et al. 1921, Churchill and Lewis 1924, Fuller 1974). Juvenile mussels employ foot (pedal) feeding, and are thus suspension feeders (Yeager et al. 1994). Foods of juvenile freshwater mussels up to two weeks old include bacteria, algae, and diatoms with amounts of detrital and inorganic colloidal particles (Yeager et al. 1994). Specific food habits of the purple bankclimber are unknown, but are likely similar to those of other freshwater mussels.

REPRODUCTION AND DEVELOPMENT: Females of the purple bankclimber with viable glochidia were found in the Ochlockonee River from February through April when water temperatures ranged from 46.4 to 59.0 degrees Fahrenheit (O’Brien and Williams 2002). This indicates that it is a late winter-early spring releaser that may or may not be a parent overwintering species, dependent upon when fertilization takes place. Females expelled narrow lanceolate-shaped conglutinates (1.0 to 1.5 cm (0.4 to 0.6 in)long) that remain viable for three days after release. The white structures, which are two-glochidia thick, are generally released singly although some are paired, being attached at one end (O’Brien and Williams 2002). Rigid when aborted prematurely (containing only eggs), conglutinates with mature glochidia easily disintegrate presumably facilitating host infection. Glochidial morphology was described and figured by O’Brien and Williams (2002).

The eastern mosquitofish (Gambusia holbrooki), blackbanded darter (Percina nigrofasciata), guppy (Poecilia reticulata) and greater jumprock transformed glochidia of the purple bankclimber during laboratory infections (O’Brien and Williams 2002, P.D. Johnson, Tennessee Aquatic Research Institute [TNARI], pers. comm. 2003). Only the eastern mosquitofish was effective at transforming glochidia (100 percent transformation rate), with the percentages for the blackbanded darter and guppy being under 33 percent. Transformation on eastern mosquitofish occurred in 17 to 21 days at temperatures of 68.9 + 5.4 degrees Fahrenheit (O’Brien and Williams 2002). Only one glochidium was successfully transformed on the greater jumprock during preliminary trials and occurred after 52 days (Johnson, TNARI, pers. comm. 2003). The eastern mosquitofish occupies stream margins in slower (or slack) currents (Lee et al. 1980), and is considered a secondary host fish since the purple bankclimber is more of a channel species (Williams and Butler 1994). The primary host species for this mussel remains unknown (O’Brien and Williams 2002).

RANGE AND POPULATION LEVEL: The type locality of the purple bankclimber was restricted to the Chattahoochee River, Columbus, Georgia, by Clench and Turner (1956). This large species is virtually restricted to Apalachicola-Chattahoochee-Flint (ACF) Basin main stems and the Ochlockonee River in Florida and Georgia (Clench and Turner 1956, Williams and Butler 1994, Brim Box and Williams 2000). Generally distributed in the Flint, Apalachicola, and Ochlockonee Rivers, it was also known from the lower halves of the Chattahoochee and Chipola Rivers, and from two tributaries in the Flint River system. Heard (1979) erroneously reported it from the Escambia River system (Williams and Butler 1994).

Subpopulations from the Chattahoochee River have apparently been extirpated save for a single live specimen found in 2000 (C. Stringfellow, Columbus State University, pers. comm., 2000). In addition, it is no longer known from the Line and Ichawaynochaway Creeks, and has not been seen live in the Chipola River since 1988. Within portions of the Flint and Ochlockonee Rivers, the purple bankclimber occurs more sporadically than it did historically. Most occurrences in the Ochlockonee River are above Talquin Reservoir. An anomalous small stream occurrence (a single specimen from an unnamed tributary of Mill Creek, Flint River system) was discovered during the status survey (USFWS 1998). Overall, 34 subpopulations of purple bankclimber currently persist (Table 7, USFWS 2003).

During the status survey, an average of 54 specimens of the purple bankclimber was recorded from 41 sites rangewide (USFWS 1998), 30 sites occurring in the ACF Basin (Brim Box and Williams 2000). The Corps completed mussel surveys at potential dredged material disposal sites, slough locations, and other main channel areas within the Apalachicola and Chipola rivers (Miller 1998, Miller 2000, Miller, ERDC pers. comm. 2003). The purple bankclimber was found at 10 sites. Limited quantitative sampling for the purple bankclimber has been conducted in the upper Apalachicola and Ochlockonee Rivers. Six 2.7 square feet quadrat samples taken below Jim Woodruff Dam on the former river revealed approximately one specimen per square foot of substrate when sieved (Richardson and Yokley 1996). Four 97-square foot quadrat hand-picked samples in the Ochlockonee River in 1993 recorded purple bankclimber densities averaging 0.34 per square foot (J. Brim Box, USGS, unpub.data).

HABITAT: The purple bankclimber inhabits small to large river channels in slow to moderate current over sand or sand mixed with mud or gravel substrates (Williams and Butler 1994). Over 80 percent of the specimens located during the ACF Basin portion of the status survey were found at sites with a substrate of sand/limestone (Brim Box and Williams 2000). ACF Basin collections were often in waters over 10 feet in depth.

PAST THREATS: The abundance and distribution of the purple bankclimber decreased historically from habitat loss and degradation (Williams et al. 1993, Neves 1993) caused by impoundments (Talquin Reservoir), sedimentation and turbidity, dredging and channelization, and contaminants contained in numerous point and nonpoint sources. A comprehensive review of these past threats is provided elsewhere (USFWS 2003, Brim Box and Williams 2000, Butler 1993, Richter et al. 1997, Watters 1997, Neves et al. 1997). However, the histories of anthropogenic impacts specifically to the Ochlockonee River drainage have not been summarized. These habitat changes have resulted in significant extirpations (localized loss of populations), restricted and fragmented distributions, and poor recruitment of young.

CURRENT THREATS: Habitat loss and degradation (Williams et al. 1993, Neves 1993) primarily caused by contaminants contained in point and nonpoint source discharges, sedimentation and erosive land practices, water quantity and withdrawal, construction of new impoundments, and alien species are primary threats to the purple bankclimber (USFWS 2003).

Sediment samples from various ACF Basin streams tested for heavy metals that are known to be deleterious to mussels had concentrations markedly above background levels (Frick et al. 1998), among those were copper (throughout the Piedmont), and cadmium (large Coastal Plain tributaries of the Flint River). Past episodes of significant heavy metal contamination of ACF Basin streams may continue to impact mussel faunas. An estimated 950 million gallons of chemical-laden rinse, stripping, cleaning, and plating solutions were discharged indirectly into the Flint River (P. Laumeyer, USFWS, pers. comm., 1994) over a several year period. Concentrations of heavy metals (e.g., chromium and cadmium) in Asian clam, Corbicula fluminea (Muller 1774), and sediment samples were elevated downstream from two abandoned battery salvage operations on the Chipola River (Winger et al. 1985). Chromium concentrations found in sediments from Dead Lake downstream in the Chipola River (Winger et al. 1985) are known to be toxic to mussels (Havlik and Marking 1987).

Agricultural sources of contaminants in the ACF and Suwannee basins include nutrient enrichment from poultry farms and livestock feedlots, and pesticides and fertilizers from row crop agriculture (Couch et al. 1996, Frick et al. 1998, Berndt et al. 1998). Nitrate concentrations are particularly high in surface waters downstream of agricultural areas (Mueller et al. 1995; Berndt et al. 1998). A study by the U.S. Soil Conservation Service (USSCS; now the Natural Resources Conservation Service [NRCS]) in the Flint River system determined that between 72 and 75 percent of the nutrients entering Lake Blackshear were derived from agricultural sources (USSCS 1993). Stream ecosystems are impacted when nutrients are added at concentrations that cannot be assimilated (Stansbery 1995). The effects of pesticides on mussels may be particularly profound (Fuller 1974, Havlik and Marking 1987, Moulton et al. 1996, Fleming et al. 1995). Organochlorine pesticides were found at levels in ACF Basin streams that often exceeded chronic exposure criteria for the protection of aquatic life (Buell and Couch 1995, Frick et al. 1998). Once widely used in the ACF Basin (Buell and Couch 1995), these highly toxic compounds are persistent in the environment, and are found in both sediments and the lipid reservoir of organisms (Day 1990, Burton 1992). Commonly used pesticides have been directly implicated in a North Carolina mussel dieoff (Fleming et al. 1995). Cotton is raised extensively in much of the Apalachicolan Region inhabited by these mussels. One of the most important pesticides used in cotton farming, malathion, is known to inhibit physiological activities of mussels (Kabeer et al. 1979) that may decrease the ability of a mussel to respire and obtain food. This chemical may pose a continuing threat to some populations of these mussels.

Many pollutants in the ACF Basin originate from urban stormwater runoff, development activities, and municipal waste water facilities, primarily in the Piedmont (Frick et al. 1998). Urban catchments in Piedmont drainages have higher concentrations of nutrients, heavy metals, pesticides, and organic compounds than do agricultural or forested ones (Lenat and Crawford 1994, Frick et al. 1998), and at levels sufficient to significantly affect fish health (Ostrander et al. 1995). Within the Suwannee River basin, nutrient concentrations were greater in agricultural areas and nitrates were found to exceed U.S. Environmental Protection Agency (EPA) drinking water standards in 20 percent of the surficial aquifer groundwater samples (Berndt et al. 1998). Pesticide concentrations were found to exceed criteria for protection of aquatic life mostly in urban areas. Currently, there are discharges from 137 municipal waste water treatment facilities in the ACF River basin alone (Couch et al. 1996). Although effluent quality has improved with modern treatment technologies and a phosphate detergent ban, hundreds of miles of streams in the ACF and Ochlockonee basins in Alabama, Florida, and Georgia, as identified in reports prepared by the water quality agencies of these states under Section 305(b) of the Clean Water Act, do not meet water use classifications.

Since approximately 29 percent of the ACF Basin is in agriculture (Frick et al. 1998), sedimentation from agricultural sources is probably significant. According to USSCS (1993), 89 percent of the sediments entering Lake Blackshear on the Flint River are derived from agricultural sources. The lower Flint River system serves as the heart of numerous mussel species’ range and is a major agricultural center. This area has experienced “severe losses of topsoil and nutrient additions to local streams due to agriculture” (Neves et al. 1997), and has profoundly affected the biota of surface and ground waters there (Patrick 1992). Despite the implications, only a few studies (e.g., Cooper 1987, Stewart and Swinford 1995) have specifically attributed changes in mussel populations to sediments derived from agricultural practices.

Many southern streams have increased turbidity levels due to siltation (van der Schalie 1938). The purple bankclimber attracts host fishes with visual cues, luring fish into perceiving that their glochidia are prey items. Such a reproductive strategy depends on clear water during the critical time of the year when mussels are releasing their glochidia (Hartfield and Hartfield 1996). Turbidity is a limiting factor impeding sight-feeding fishes (Burkhead and Jenkins 1991). In addition, mussels may be indirectly affected when turbidity levels significantly reduce light available for photosynthesis and the production of unionid food items (Kanehl and Lyons 1992).

Water quantity is becoming more of a concern in maintaining mussel habitat in the Apalachicolan Region. The potential impacts to mussels, their host fishes, and their respective habitats from ground water withdrawal may be profound. Within the Flint River basin, decreases in flow velocity and dissolved oxygen were highly correlated to mussel mortality (Johnson et al. 2001). Low DO conditions in stagnating stream pools due to drought conditions are having a disastrous effect on these mussels. Mussel mortality increases dramatically as DO decreases below 5 mg/L (Johnson et al. 2001).

Maintaining vegetated riparian buffer zones adjacent to stream banks is a well-known method of reducing stream sedimentation and other runoff (Allan and Flecker 1993, Lenat and Crawford 1994). Buffers reduce impacts to fish and other aquatic faunas (Armour et al. 1991, Naiman et al. 1988, Osborne and Kovacic 1993, Belt and O’Laughlin 1994, Penczak 1995, Rabeni and Smale 1995), and are particularly crucial for mussels (Neves et al. 1997). Riparian forest removal in southeastern streams and subsequent sedimentation has been shown to be detrimental to fish communities (Burkhead et al. 1997, Jones et al. 1999). Particularly affected in the study by Jones et al. (1999) were benthic-dependent species (e.g., darters, benthic minnows, sculpins), which were found to decrease in abundance with longer deforested patches of riparian area. Benthic-dependent fishes, themselves disproportionately imperiled (Burkhead et al. 1997), commonly serve as hosts for numerous imperiled mussel species (Watters 1994), probably including the purple bankclimber.

Exposure Scenario Summary Table for the Purple Bankclimber

Species	Life Stage	Habitat Type	Exposure Route	Diet	Significant Interspecies Relationships
Purple Bankclimber	glochidia	parasite	contact with water, diet	fish body fluids	host fish(es) unknown
	juvenile/ adult	sediment dweller	contact & ingestion of water, diet, sediment	filter feeder (bacteria, algae, detritus, sediment)

CONSERVATION MEASURES:

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