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Impact of drought on predation of a state-threatened mussel, Potamilus amphichaenus.

Freshwater mussels often occur in dense multispecies beds in aquatic ecosystems performing important functional roles such as removing suspended organic matter, moving sediments, and providing habitat for other animals (Strayer et al., 1997; Vaughn and Hakencamp, 2001). Over the last century, populations of North American mussels have decreased with 35 species considered extinct and ca. 50% imperiled (Shannon et al., 1993; Williams et al., 1993; Neves et al., 1997; Vaughn, 1997). Historically, freshwater mussels were extremely abundant in rivers of the southeastern United States (Strayer et al., 1994; Parmalee and Bogan, 1998). There are ca. 50 species of unionid mussels in Texas with a distinct composition in eastern Texas (Neck, 1982; Howells et al., 1996). A corresponding decline has occurred in populations in Texas (Neck, 1984).

A severe drought occurred in eastern Texas during 2011 with deficits in precipitation of >50.8 cm in eastern Texas throughout 2011 (United States Geological Survey, in litt.). The lack of rainfall resulted in the drying of perennial streams and reduced flows in major streams and rivers. Because freshwater mussels are limited in their ability to migrate, decreases in depth of water and velocity of flow may cause mussels to become stranded (Golladay et al., 2004) or exposed in very shallow water. Emersion of freshwater mussels may make them more vulnerable to predation (J. B. Box and M. Freeman, in litt.). The capture of unionid mussels by terrestrial mammals is not often directly observed, but the empty shells are readily collected and provide evidence of predation (Van Cleave, 1940).

The freshwater mussel Potamilus amphichaenus is currently considered a legally-threatened species in Texas (Texas Parks and Wildlife Department, in litt.). Potamilus amphichaenus also is in consideration for federal listing with the United States Fish and Wildlife Service. From 1898, when the species was described, through 1994, only 150 specimens had been reported (Howells et al., 1996). It occurs in eastern Texas in the Sabine, Neches, and Trinity rivers systems. By 2010, just over 300 specimens were recorded (R. G. Howells, in litt.). Although more recent citations suggest it may not be uncommon in the Sabine River (Ford et al., 2009).

Specimens of Potamius amphichaenus were collected in the Sabine River in July-August 2011 in three sites upstream of Toledo Bend Lake. At the time of collection, the sampling areas contained a wide reach of water of only 0.25 m in depth. Mussels were easily visible in the sandy substrate in shallow water. We collected 79 recently deceased specimens by walking ca. 150 m of each reach.

Of the specimens collected, 58 had signs of predation including marks from scratches and bites. No live specimens with such marks were found. All predation occurred on P. amphichaenus that were <100 mm in length and percentage of P. amphichaenus preyed upon decreased according to size (Table 1). We documented where marks occurred on the shell (anterior, posterior, and ventral) and used chi-square test to determine if a specific part of the shell was preferentially attacked. The results from the chi-square test indicate that predators more frequently attacked the anterior margin ([chi square] = 25.138, df = 1, P < 0.001). Howells et al. (2000) observed similar predation on this and other unionids during dewatering in the Neches River drainage. They also noted particularly heavy predation on thin-shelled mussels (like P. amphichaenus) rather than on more heavy-shelled taxa assumed to be resistant to attacks. Similar predation has been noted at a site in the lower Trinity River (R. G. Howells, in litt.).

In P. amphichaenus, both ends have gapes, but the pedal gape anteriorly is largest. Potamilus amphichaenus have a noticeable opening exposing tissue towards the anterior end of the shell (pedal gape), which is oriented downward into the substrate and another posteriorly (siphonal gape) which projects upwards into the column of water (Howells et al., 1996). Predators may focus attacks on these gapes to access soft tissues as well as the thinnest areas of the shell. The rounded end near the umbo is the anterior and is the thickest part of the shell while the posterior end is the thinner area. The preference for the anterior end by predators suggests that this may be a direct result of accessibility of soft tissue as the predator removes it from the sand rather than a result of thickness of shell. Wading birds, fish, and several species of terrestrial mammals are common predators of freshwater mussels; however, the presence of large numbers of tracks of Procyon lotor, raccoon, throughout the reaches suggests that this species was the likely predator in this case.

The number of shells from predation found during the drought and the lack of live specimens suggests that P. amphichaenus is strongly affected by predation during conditions of low flow. Predation on these unionids in the Sabine River during low flow is likely contributing to the decline of this species throughout eastern Texas. The increased occurrence of drought and increasing withdrawal to meet needs of the state for water will likely increase mortality of P amphichaenus related to predation. The ability of P. lotor and other predators to locate and exploit freshwater mussels may have implications for the conservation of rare and endangered mussels, many of which have very limited distributions (Neves and Odom, 1989; Metcalfe-Smith et al., 1998).

We thank the Texas Parks and Wildlife Department for funding. We also thank R. Howells for reviewing an early draft of this manuscript and J. Bouse for assistance with fieldwork.


FORD, N. B., J. GULLETTE, AND M. E. MAY. 2009. Diversity and abundance of unionid mussels in three sanctuaries on the Sabine River in Northeast Texas. Texas Journal of Science 61:279-274.

GOLLADAY, S. W., P. GAGNON, M. KEARNS, J. M. BATTLE, AND D. W. HICKS. 2004. Response of freshwater mussel assemblages (Bivalvia: Unionidae) to a record drought in the Gulf Coastal Plain of Southwestern Georgia. Journal of North American Benthological Society 23:494-506.

HOWELLS, R. G., C. M. MATHER, AND J. A. M. BERGMENN. 2000. Impacts of dewatering and cold on freshwater mussels (Unionidae) in B.A. Steinhagen Reservoir, Texas. Texas Journal of Science 52(2):93-104.

HOWELLS, R. G., R. W. NECK, AND H. D. MURRAY. 1996. Freshwater mussels of Texas. Texas Parks and Wildlife Press, Austin, Texas.

METCALFE-SMITH, J. L., S. K STATON, G. L. MACKIE, AND N. M. LANE. 1998. Selection of candidate species of freshwater mussels (Bivalvia: Unionidae) to be considered for national status designation by COSEWIC. Canadian Field Naturalist 112:425-440.

NECK, R. W. 1984. Restricted and declining nonmarine mollusks of Texas. Texas Parks and Wildlife Department, Technical Series 3:1-17.

NECK, W. 1982. Preliminary analysis of the ecological zoogeography of the freshwater mussels of Texas. Pages 33-42 in Proceedings of a symposium on recent benthological investigations in Texas and adjacent states. Texas Academy of Science, Austin, Texas.

NEVES, R. J., A. E. BOGAN, J. D. WILLIAMS, S. A. AHLSTEDT, AND P. W. HARTFIELD. 1997. Status of aquatic nrollusks in the southeastern United States: a downward spiral of diversity. Pages 43-86 in Aquatic fauna in peril: the southeastern perspective special publication 1 (G. W. Benz and D. E. Collins, editors). Southeast Aquatic Research Institute, Decatur, Georgia.

NEVES, R. J., AND M. C. ODOM. 1989. Muskrat predation on endangered freshwater mussels in Virginia. Journal of Wildlife Management 53:934-941.

PARMALEE, P. W., AND A. E. BOGAN. 1998. The freshwater mussels of Tennessee. University of Tennessee Press, Knoxville, Tennessee.

SHANNON, L., R. G. BIGGINS, AND R. E. HYLTON. 1993. Freshwater mussels in peril; perspectives of the U.S. Fish and Wildlife Service. Pages 66-68 in Conservation and management of freshwater mussels. Proceedings of a UMRCC symposium, 12-14 October 1992, St. Louis, Missouri (K S. Cummins, A. C. Buchanan, and L M. Koch, editors). Upper Mississippi River Conservation Committee, Rock Island, Illinois.

STRAYER, D. L., D. C. HUNTER, L. C. SMITH, AND C. K. BORG. 1994. Distribution, abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River. Freshwater Biology 31:239-248.

STRAYER, D. L., S. CLAYTOOL, AND S.J. SPRAGUE. 1997. Assessing unionid populations with quadrats and timed searches. Pages 163-169 in Conservation and management of freshwater mussels. II. Initiatives for the future. Proceedings of a Symposium, 16-18 October 1995, St. Louis, Missouri (K. S. Cummings, A. C. Buchanan, C. A. Mayer, and T. J. Naimo, editors). Upper Mississippi River Conservation Committee, Rock Island, Illinois.

WILLIAMS, J. D., M. L. WARREN, JR., K. S. CUMMINGS, J. L. HARRIS, AND R. J. NEVES. 1993. Conservation status of the freshwater mussels of the United States and Canada. Fisheries 18:6-22.

VAN CLEAVE, H. J. 1940. Ten years of observation on a fresh-water mussel population. Ecology 21:363-370.

VAUGHN, C. C. 1997. Catastrophic decline of the mussel fauna of the Blue River, Oklahoma. Southwestern Naturalist 42:333-336.

VAUGHN, C. C., AND C. C. HAKENKAMP. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46:1431-1446.

Submitted 12 March 2012. Accepted 30 January 2014.

Associate Editor was James H. Kennedy.


Department of Biology, Miami University, Oxford, OH 45056-1400 (ADW)

Department of Biology, University of Texas at Tyler, Tyler, IX 75701 (NBF)

* Correspondent:
Table 1--Mean ([+ or -]1 SD; millimeters) length, width, and
height for three size-classes of Texas heelsplitter, Potamilus
amphichaenus, found deceased clue to predation in the Sabine
River, eastern Texas. Percentage of total mussels with marks
from scratches or bites is given.

Size class           Length                 Width

<100          89.50 [+ or -] 8.03   51.40 [+ or -] 5.35
101-120      111.93 [+ or -] 5.12   61.96 [+ or -] 4.15
121-148      130.00 [+ or -] 8.20   73.36 [+ or -] 4.88

Size class          Height           Percentage with
                                   marks from predation

<100          7.60 [+ or -] 4.55          100.0
101-120      36.74 [+ or -] 3.32          84.8
121-148      43.82 [+ or -] 4.49          54.5
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Author:Walters, Ashley D.; Ford, Neil B.
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1USA
Date:Dec 1, 2013
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