||Margaritifera marrianae Johnson, 1983
||Alabama Pearlshell, Alabama Pearl Shell
||The family Margaritiferidae is recognized based on the recent work of Smith (1986) and Smith and Wall (1984). The monotypic genus Cumberlandia has generally has been classified in the family Margaritiferidae; however, preliminary analyses of electrophoretic data led Davis and Fuller to lump the margaritiferids with the Unionidae (Davis and Fuller, 1981). Smith and Wall (1984) reinstated the Margaritiferidae to familial rank following and extensive examination and analysis of morphological characters. Some anatomical data on stomach anatomy (Smith, 1986) indicates Cumberlandia may require reduction to subgeneric level. This is supported by Davis and Fuller (1981), Ziuganov et al. (1994), Smith (2001), and Huff et al. (2004). Smith (2001) analyzied the taxonomic placement of the margaritiferid genera, recognizing Pseudunio, Margaritifera, and Margaritinopsis as valid based largely on morpological characters. Contrary to Smith (2001), Huff et al. (2004) investigated phylogenetic relationships using sequence data from five molecular markers and concluded recognition of of at least Margaritifera margaritifera, Margaritifera laevis, Margaritifera falcata, and Margaritifera auricularia with the following relationships: Cumberlandia + Margaritifera auricularia; Margaritifera falcata (Margaritifera marrianae + Margaritifera laevis); and to a lesser degree Dahurinaia dahurica + Margaritifera margaritifera. Margaritifera marianae was originally believed to be an eastern population of Margaritifera hembeli (Clench and Turner 1956). Its specific characters were recognized by Johnson (1983).
|Red List Category & Criteria:
||Cummings, K. & Cordeiro, J.
||Bohm, M., Seddon, M. & Collen, B.
||Bogan, A., Richman, N., Dyer, E., Soulsby, A.-M., Whitton, F., Kasthala, G., McGuinness, S., Milligan, HT, De Silva, R., Herdson, R., Thorley, J., McMillan, K., Collins, A., Offord, S. & Duncan, C.
Margaritifera marrianae has been assessed as Endangered under criterion A2c as it is a severely declining regional endemic that has been extirpated from most (70%) of its historic range. Mussels of the genus Margaritifera are fairly long-lived, suggesting long generation lengths, so that it can be assumed that these historical declines, which have primarily taken place over the course of the 20th century, have occurred over three generations. Throughout its current range it is rare and faces major threats. Only two of the four extant populations show evidence of recruitment and all are in small reaches with limited numbers of individuals. No conservation measures are in place to safeguard the species, and this needs to be rectified.
In 1996 it was assessed as Endangered, based on estimates from Bogan that there was 50% decline in range due to habitat destruction and introduction of non-native species (Seddon, pers. comm., 2012) and estimated presence in small range with few locations, based on threats to the species.
|Previously published Red List assessments:|
- 2000 – Endangered (EN)
- 1996 – Endangered (EN)
- 1994 – Indeterminate (I)
- 1990 – Indeterminate (I)
- 1988 – Indeterminate (I)
- 1986 – Indeterminate (I)
|Range Description:||In the Conecuh River drainage, this species is known from several tributaries in Conecuh and Crenshaw counties. Mobile Basin populations are localized, occurring primarily in the Alabama River drainage, where they are restricted to the Big Flat and Limestone Creek systems, Monroe County. An additional population is known from the Buttahatchee River, Marion County, in the Tombigbee River drainage. It appears to be extant only in two small Conecuh River tributaries in Conecuh County (Pilarczyk et al. 2006). An updated account from Williams et al. (2008) reports the species to be known from only a portion of the Conecuh River drainage in Conecuh and Crenshaw counties, Alabama, and localized populations in the Mobile Basin. Its extent of occurrence is estimated as less than 250 km2, with an area of occupancy of between 20 and 100 km2.|
United States (Alabama)
|♦ Estimated area of occupancy (AOO) - km2:||20-100|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The distribution of this species has been greatly reduced from the historic range, although the historical range was always rather narrow. However, there has also been a great reduction in occupied habitat. Once common in streams within its range, it is now limited to three strong populations in the center of its range and is found disjunctly in five others; some of these recent records being of dead shells only (Shelton 1996). Only three populations of Alabama Pearlshells were confirmed by recent survey efforts: Hunter, Jordan, and Little Cedar Creeks, all Murder Creek drainage (West Fork Choctawhatchee basin), Conecuh County, Alabama; however, the status of the Hunter Creek population is currently in doubt (eight individuals in 1998, none subsequently) (USFWS 2003). Pilarczyk et al. (2006) recorded recent collections of this species at Jordan Creek (on the West Fork of the Choctawhatchee River, Choctawhatchee River drainage) in southern Alabama and historically in Bottle Creek in the 1990s (although it still might be present in this drainage; Mirarchi et al. 2004). Williams et al. (2008) summed up this species' Alabama distribution as extant only in two small Conecuh River tributaries in Conecuh Co. (see Pilarczyk et al. 2006).|
Historically common within its range, it is now rare within most extant occurrences with low density levels where found. Jordan Creek supports the highest numbers of Alabama Pearlshell (63 individuals reported in 1998; 13 in 2004), and the presence of a few juvenile/subadult individuals indicates some level of recruitment in this population (Pilarczyk et al. 2006). However, Pilarczyk et al. (2006) did not find the species in any of the other 23 sites surveyed in the Choctawhatchee and Yellow River drainages. Little Cedar Creek also contains good numbers of Alabama Pearlshells (54 individuals reported in 1998) and shows the greatest variety of age classes of the three populations. Both Jordan and Little Cedar Creeks continued to sustain good populations with considerable evidence of recent recruitment in 1999 (USFWS 2003). The Hunter Creek population is even smaller than these (USFWS 2003).
Much of the former habitat has been impacted by siltation and unrestricted cattle access. Large numbers of specimens in museum collections represent collections that cannot be duplicated with current low densities without threatening the further existence of the species. Of the three viable populations known, two show evidence of recruitment. The Hunter Creek population appears to be geriatric and non-reproducing (Shelton 1997) and may now be extirpated (USFWS 2003). Evidence suggests that much of the decline of this species has occurred within the past few decades. The Alabama Pearlshell was relatively common in localized portions of Limestone Creek and its tributary Brushy Creek, Alabama River drainage, as recently as 1974. Twelve specimens of the Alabama Pearlshell were collected from Horse Creek, Conecuh River drainage, Crenshaw County, as recently as 1981. Records of occurrence exist for Autrey Creek from 1964. The most recent records from other historically occupied sites in Murder Creek proper, three of its tributaries, and Burnt Corn Creek, date from the early 1900s. The species has apparently been extirpated from all these localities (USFWS 2003). The only record from the Buttahatchee River is a single specimen collected in 1909 (Williams et al. 2008).
Pilarczyk et al. (2006) found the species historically in two out of 24 sites re-surveyed (Bottle creek and Jordan creek), however the last survey in 2004 found individuals only at one site (Jordan creek).
|Current Population Trend:||Decreasing|
|♦ Number of mature individuals:||250-2500|
|♦ Population severely fragmented:||No|
|Habitat and Ecology:||This species inhabits headwater streams with slow to moderate current in mixed sand and gravel substrates, but can occasionally be found in sandy mud (Williams et al. 2008). Frierson (1927) listed it from soft water streams from the pine barrens of southeastern Alabama, but incorrectly reported it as occurring “only in water free from lime”. To the contrary, the species often occurs in streams with abundant limestone and groundwater inflow. Substrates in this region tend to be sandy and high accumulations of detritus (in conjunction with the poor buffering quality) result in water stained brown by elevated concentrations of tanins. Water temperatures tend to be moderated by the influx of springs. Shelton (1997) reports the habitat for the species to be headwater streams of slow to moderate current velocities with substrates consisting of sand, sandy mud, gravel, or a sand gravel mixture with an average depth of less than 0.5 meters.|
This species has been reported to occur in male-female pairs, with the male upstream of the female (Shelton 1997). This was determined based on sexual dimorphism in shell morphology. However, other workers discount the visual recognition of sexual dimorphism in Margaritifera (R. Araujo pers comm. 2010). The species appears to be a long-term brooder. Gravid females have been reported in December (Shelton 1997). Its glochidial hosts are unknown.
Direct life-history data are not available for this species. Freshwater mussels are highly variable in their longevity from species to species (e.g. Haag and Rypel 2011). Studies have shown longevity of Margaritifera species to range from 28 to 190 years (from populations of M. falcata and M. margaritifera: average of 75 years; Haag and Rypel 2011). Various species of mussel were found to mature between two and nine years of age (Haag and Staton 2003). Based on this, and using 28 to 75 years as an estimate of longevity, we estimate generation length (calculated as the average age of a parent in the population (assuming mussels reproduce until they die)), as 15-42 years, with three generations spanning 45-126 years. Historical declines due to habitat alteration and pollution therefore fall well within this timeframe, having occurred primarily in the 20th century.
|Congregatory:||Congregatory (and dispersive)|