Freshwater Mussel (Bivalvia: Unionidae) Distributions and Habitat Relationships in the Navigational Pools of the Allegheny River, Pennsylvania Author(s): Tamara A. Smith and Elizabeth S. Meyer Source: Northeastern Naturalist, 17(4):541-564. 2010. Published By: Humboldt Field Research Institute DOI: 10.1656/045.017.0403 URL: http://www.bioone.org/doi/full/10.1656/045.017.0403
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2010
NORTHEASTERN NATURALIST
17(4):541–564
Freshwater Mussel (Bivalvia: Unionidae) Distributions and Habitat Relationships in the Navigational Pools of the Allegheny River, Pennsylvania Tamara A. Smith1,2 and Elizabeth S. Meyer3,* Abstract - The main-stem Allegheny River is nationally recognized for its freshwater mussel (Unionidae: Bivalvia) diversity; however, habitat disturbance and degradation may have triggered the decline and loss of mussel communities in the lower river, where lock and dam structures restrict the free flow of water and sand and gravel removal threaten limited habitat. We examined mussel diversity and abundance across 75 transects throughout navigational pools and recorded 21 live native mussel species, including federally endangered Pleurobema clava (Clubshell) and Epioblasma torulosa rangiana (Northern Riffleshell) and several species with state endangered or threatened status. Riverine species richness and counts were significantly higher in the most-upstream portions of the upper pools, indicating that areas with consistent flows and suitable substrate just downstream of the dams may provide refugia for riverine freshwater mussel species. Sand, gravel, cobble, boulder, and organic debris had significant positive effects on riverine and facultative counts, while clay, bedrock, and woody debris had significant negative effects. Silt and woody debris had significant negative effects on riverine species richness, and sand and gravel had significant positive effects. These data will help identify sensitive areas for future protection and provide baseline data for monitoring future trends. The protection of relatively shallow areas with suitable substrates not yet impacted by dredging operations will be important to sustain remaining freshwater mussel populations in these pools.
Introduction Freshwater mussels are considered the most imperiled fauna in North America, with approximately 213 of the 297 recognized taxa considered endangered, threatened, or of special concern (Lydeard et al. 2004, NatureServe 2009, Ricciardi and Rasmussen 1999, Williams et al. 1993). Several species occur at their highest densities within their global range in the Allegheny River system, including Epioblasma torulosa rangiana (Northern Riffleshell) and Pleurobema clava (Clubshell), both federal and state endangered species. The Allegheny River contains two candidates for federal endangered listing status; Villosa fabalis (Rayed Bean) and Plethobasus cyphyus Rafinesque (Sheepnose). In addition, Epioblasma triquetra Rafinesque (Snuffbox), listed as endangered in Pennsylvania and 1 Western Pennsylvania Conservancy, Northwest Field Station, 11881 Valley Road, Union City, PA 16438. 2Current address - US Fish and Wildlife Service, Twin Cities Ecological Services Field Office, 4101 American Boulevard East, Bloomington, MN 55425. 3Western Pennsylvania Conservancy, 800 Waterfront Drive, Pittsburgh, PA 15222. *Corresponding author -
[email protected].
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two additional species of special concern in Pennsylvania, Amblema plicata (Three-ridge) and Pleurobema sintoxia (Round Pigtoe), are also found in the Allegheny River (NatureServe 2009). The diverse mussel fauna of the Allegheny River faces threats from habitat alteration, loss, and degradation. A series of 8 lock-and-dam structures were constructed on the lower Allegheny River during the late 1890s to the 1930s to create deep waters for navigation purposes. In addition, the Kinzua Dam, located 218 river kilometers upstream of Lock and Dam 9 near Warren, PA, is managed for flood control and to maintain flows during dry periods (US Army Corps of Engineers 2010a). Stream channel alterations and dams are documented threats to the viability of freshwater mussels (Watters 2000). Furthermore, active sand and gravel mining occurs within the navigational pools, and may permanently alter mussel habitat (Brown et al. 1998, Hubbs et al. 2003, Kondolf 1997, Meador and Layher 1998). However, areas within these channels not impacted by dredging and with consistent flows may serve as refugia for riverine freshwater mussel and host fish species. Early studies documented approximately 35 species in the Allegheny River (Ortmann 1919), and many of these species are now thought to be extirpated in this portion of the river. The portion of the Allegheny River downstream of the Kinzua Dam in Pennsylvania still maintains populations of approximately 30 unionid species (Villella and Nelson 2006). French Creek, a tributary to the Allegheny River, still holds over 26 species (Smith and Crabtree, in press). Recent project-specific surveys have been conducted in the navigational pools, usually as a direct response to dredging or construction permits (US Fish and Wildlife 2004). However, no comprehensive mussel study has been completed in the impounded navigational pools in the Allegheny River. The goals of this study were to initiate a comprehensive study of the freshwater mussel populations in the lower Allegheny River navigational pools 4 through 8 and to look for patterns in mussel distribution in relation to environmental variables and the position within the river. Identifying areas where rare mussels persist in these pools and environmental clues as to where others are likely to exist would provide baseline data that could inform decisions about protection and restoration efforts. For example, this data could be used to help decide locations of ecological reserves or make informed decisions on where to focus restoration efforts. Additionally, this information could lead to protection efforts for remaining freshwater mussel habitat, such as locations with designated limitations on commercial sand and gravel mining operations. Methods Study location The Allegheny River (610 km) flows from Potter County, PA north through Cattaraugus County in New York State, then fl ows south in
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Pennsylvania until its confluence with the Monongahela River to form the Ohio River in Pittsburgh, PA. A series of locks and dams were constructed on the Allegheny River between 1897 and 1938, resulting in 116 km of slackwater navigation from Pittsburgh to just above East Brady, PA (US Army Corps of Engineers 2010b). This study took place in navigational pools 4, 5, 6, 7, and 8 (Fig.1).
Figure 1. Transect locations in the Allegheny River navigational pools 4, 5, 6, 7, and 8. The insert magnifies a portion of pool 6, where transect locations were dense. River kilometers are abbreviated as RKM.
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Transect selection Our surveys targeted relatively undisturbed areas believed to be suitable habitat for mussels. We sampled relatively shallow areas (10 m deep; over 95% of all live mussels were found in |z|) = 0.000) and Fragile Papershell (Est. = 1.121, SE = 0.570, Z value = 1.967, Pr(>|z|) = 0.049). Maximum depth squared had significant negative effects on Mucket (Est. = -0.142, SE = 0.061, Z value = -2.335, Pr(>|z|) = 0.020), Spike (Est. = -0.225, SE = 0.059, Z value = -3.838, Pr(>|z|) = 0.000), and Fatmucket (Est. = -0.102, SE = 0.049, Z value = -2.091, Pr(>|z|) = 0.037). These results indicate a nonlinear relationship between maximum depth and Mucket, Spike, and Fatmucket. In other words, after an intermediate depth (approximately 4 m), the presence of these three species declines. Silt had significant negative effects on Pocketbook (Est. = -0.074, SE = 0.037, Z value = -1.988, Pr(>|z|) = 0.047) and Plain Pocketbook (Est. = -0.040, SE = 0.020, Z value = 2.011, Pr(>|z|) = 0.044) presence. Sand (Est. = 0.041, SE = 0.016, Z value = 2.513, Pr(>|z|) = 0.012) and gravel (Est. = 0.032, SE = 0.015, Z value = 2.097, Pr(>|z|) = 0.036) had significant positive effects on Mucket presence. All other environmental variables were not statistically significant. Table 7. Results of the logistic regression (656 observations, 74 groups) on the presence or absence of the 10 most common species (number of individuals > 35). Environmental variables were considered significant at P < 0.05 level; fixed effects not presented in this table or in the text were not significant. Distance from nearest upstream dam was not significant for F. flava (Wabash Pigtoe) and river kilometer (RKM) was not significant for L. costata (Flutedshell). Distance from nearest upstream dam A. ligamentina E. dilatata F. flava L. cardium L. ovata L. siliquoidea L. costata L. fragilis L. recta P. alatus
RKM
Est.
SE
Z value
Pr(>|z|)
Est.
SE
-0.612 -0.675 -0.061 -0.221 -0.362 -0.211 -0.215 -0.166 -0.262 -0.227
0.116 0.118 0.082 0.097 0.175 0.051 0.059 0.064 0.080 0.065
-5.281 -5.723 -0.745 -2.276 -2.061 -4.125 -3.640 -2.615 -3.260 -3.474
0.000 0.000 0.456 0.023 0.039 0.000 0.000 0.009 0.001 0.001
0.079 0.096 -0.058 0.031 0.101 0.021 0.026 0.055 0.039 -0.059
0.025 0.028 0.021 0.015 0.025 0.011 0.014 0.015 0.013 0.013
Z value Pr(>|z|) 3.146 3.457 -2.745 2.061 3.993 1.940 1.923 3.665 3.022 -4.447
0.002 0.001 0.006 0.039 0.000 0.052 0.054 0.000 0.003 0.000
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Discussion The Pittsburgh District of the US Army Corps of Engineers operates eight locks and dams on the Allegheny River for navigation of commercial vessels. Dams fragment mussel habitat by inhibiting longitudinal movement of host fishes and glochidia (Watters 1996). Furthermore, the impoundments provide habitat for invasive species such as Zebra Mussels, which are a documented threat to freshwater mussels (Biggins et al. 1995, Ricciardi et al. 1998, Strayer and Malcom 2007) and were present in this study. The detrimental effects of dams and impoundments on freshwater ecosystems has been widely documented (e.g., Bates 1962; Baxter 1977; Blalock and Sickel 1996; Bogan 1993; Chessman et al. 1987; Kondolf 1997; Parmalee and Hughes 1993; Porto et al 1999; Richter et al. 1997; Sickel et al. 2007; Vaughn and Taylor 1999; Watters 1996; 2000; Williams and Fuller 1992). The lock-and-dam structures on the Allegheny River have altered the river from free-flowing, well-oxygenated riffles and runs into a series of deep, slower-flowing pools or lakes (Ortmann 1909). Of the entire 22.6 million-m2 mapped area in pools 4 through 8, 37.1% is deeper than 6 m and 19.5% is deeper than 9 m (E. Long, Western Pennsylvania Conservancy, Blairsville, PA., pers. comm.; Long and Chapman 2008). Of the surveyed segments, 10.2% were in areas deeper than 6 m and 2.1% were in areas deeper than 9 m. The results of our study show that 95% of the live individuals were found in the relatively shallow areas (
