SPECIES CODE: F03N I01
STATUS: On March 16, 1998, the Ochlockonee moccasinshell was designated as Endangered throughout its entire range (USFWS 1998). A recovery plan addressing the Ochlockonee moccasinshell was finalized on October 1, 2003 (USFWS 2003).
SPECIES DESCRIPTION: The Ochlockonee moccasinshell is a small species, generally under 5.6 cm (2.2 in) in length. It is slightly elongate-elliptical in outline, the posterior end obtusely rounded at the median line, and the ventral margin broadly curved. The posterior ridge is moderately angular and covered in its entire length with well developed, irregular plications. Sculpture may also extend onto the disk below the ridge. The periostracum (outside surface of the shell) is smooth. The color is light brown to yellowish green, with dark green rays formed by a series of connected chevrons or undulating lines across the length of the shell. Internal characters include thin straight lateral teeth and compressed pseudocardinal teeth. There are two pseudocardinals and two laterals in the left valve and one pseudocardinal and one lateral in the right valve. The nacre is bluish white. The taxonomic confusion that has surrounded the genus Medionidus is summarized elsewhere (USFWS 2003).
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). Food 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 Ochlockonee moccasinshell are unknown, but are likely similar to those of other freshwater mussels.
REPRODUCTION AND DEVELOPMENT: The extreme rarity of the lampsiline Ochlockonee moccasinshell has precluded any opportunities to explore its life history. It can only be assumed that this species has similar reproductive biology traits of its congener, the Gulf moccasinshell. Therefore, it may be a parent overwintering, summer releasing species that probably utilizes darters as hosts, as does the Gulf moccasinshell, Alabama moccasinshell (Haag and Warren 1997), and Cumberland moccasinshell (Lea, 1834) (Zale and Neves 1982).
RANGE AND POPULATION LEVEL: The Ochlockonee moccasinshell was described from the Ochlockonee River, Calvary, Grady County, Georgia. This Ochlockonee River system endemic mussel was known historically from the main stem in Georgia and Florida, and the Little River (Johnson 1977, Butler 1993, Williams and Butler 1994). The Service has provided a table of occurrences of Ochlockonee moccasinshell (Table 4, USFWS 2003).
Museum records for the Ochlockonee moccasinshell indicate that it was historically common, including two Ochlockonee River sites (21 and 24 specimens collected twice from a single site in the early 1930s, 19 from another collected in 1969) (J.D. Williams, USGS, unpub. data). Even as late as the early 1970s this species was found in some numbers above Talquin Reservoir, Florida (W.H. Heard, Florida State University, pers. comm., 1994). This species may now be the rarest mussel currently inhabiting the Apalachicolan Region and is one of the rarest mussels nationwide (USFWS 2003). Only three live specimens are known to have been collected since 1974 despite concerted efforts by numerous investigators (J.D. Williams, USGS, unpub. data). The most recent live specimen was collected during the status survey in 1 of 4 hand-picked 97-square foot quadrats (J. Brim Box, USGS, unpub. data). Currently, this species persists in only a relatively short reach of Ochlockonee River above Talquin Reservoir (Table 4, USFWS 2003).
HABITAT: The Ochlockonee moccasinshell inhabits large creeks and the Ochlockonee River main stem in areas with current. Typical substrates are sand with some gravel (Williams and Butler 1994).
PAST THREATS: The abundance and distribution of the Ochlockonee moccasinshell 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: Due to the extreme rarity of the Ochlockonee moccasinshell, any adverse impacts to its habitat or an individual could result in the potential demise of the species.
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 Ochlockonee moccasinshell (USFWS 2003). Low populations levels and restricted ranges now render these mussels extremely vulnerable to toxic chemical spills and other catastrophic events, and the deleterious effects of genetic isolation.
Although effluent quality has improved with modern treatment technologies and a phosphate detergent ban, hundreds of miles of streams in the Ochlockonee basin in Georgia and Florida, as identified in reports prepared by the water quality agency of the states under Section 305(b) of the Clean Water Act, do not meet water use classifications.
Many southern streams have increased turbidity levels due to siltation (van der Schalie 1938). The Ochlockonee moccasinshell 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).
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 Ochlockonee moccasinshell.
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. 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).
Exposure Scenario Summary Table for the Ochlockonee Moccasinshell
contact & ingestion of
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