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Range extension of the freshwater mussel Potamilus purpuratus (Bivalvia: Unionidae) in Texas.
Subject:
Mussels, Fresh-water (Observations)
Mussels, Fresh-water (Natural history)
Author:
Howells, Robert G.
Pub Date:
02/01/1997
Publication:
Name: The Texas Journal of Science Publisher: Texas Academy of Science Audience: Academic; General Format: Magazine/Journal Subject: Science and technology Copyright: COPYRIGHT 1997 Texas Academy of Science ISSN: 0040-4403
Issue:
Date: Feb, 1997 Source Volume: 49 Source Issue: 1
Geographic:
Geographic Scope: Texas Geographic Code: 1U7TX Texas

Accession Number:
128664941
Full Text:
The freshwater bivalve Potamilus purpuratus is a large, distinctive unionid which occurs throughout much of the central and lower Mississippi River Valley (Cummings & Mayer 1993; Vidrine 1993). It is also known to occur in tributaries of the Gulf of Mexico east and west of the Mississippi River (Strecker 1931; Vidrine 1993).

In Texas, this species occurs from the Red River drainage southwest into the Guadalupe/San Antonio River drainage (Howells et al. 1996). Strecker (1931) did not report P. purpuratus from the Nueces or Frio rivers and Murray (1978) did not find it in a survey of Lake Corpus Christi on the lower Nueces River. Previous reports by Strecker (1931) of this species from the Devils River near its confluence with the Rio Grande were found to represent misidentified specimens (R. Neck & C. Boone, pers. comm.) of the Tampico pearlymussel Cyrtonaias tampicoensis. Metcalf (1982) did not find this species represented in the fossil assemblages of the central Rio Grande and Neck & Metcalf (1988) did not report it from the lower Rio Grande downstream from Falcon Reservoir.

Freshwater mussels not only support important commercial fisheries, but are among one of the fastest declining groups of animals in North America (Neves 1993; Williams et al. 1993). Because of this, the staff of the Texas Parks and Wildlife Department's (TPWD) Heart of the Hills Research Station began a study of Texas unionid populations in 1992, including statewide distributional surveys. From October 1993 through January 1995, populations of Potamilus purpuratus were found at several sites outside their previously known ranges. This study represents an extension of the previously known range of P. purpuratus in Texas. Voucher specimens are deposited with the holdings of the Houston Museum of Natural Science (HMNS).

Potamilus purpuratus (Lamarck)

(bleufer, blooper or blue mucket)

Material examined. -- Lake Corpus Christi, Live Oak County, Texas, 5 October 1993, two specimens (HMNS 42487); Amistad Reservoir (near confluence of Devils River), Val Verde County, Texas, 21 December 1994, two specimens (HMNS 42486); Middle Concho River upstream from Twin Buttes Reservoir, Tom Green County, Texas, 3 August 1994, two specimens (HMNS 42485).

Distributional notes. -- Survey work conducted in Lake Corpus Christi and the Nueces River just upstream of the reservoir in October 1993 revealed that P. purpuratus was one of the most abundant unionid taxa in the reservoir. It was represented by very small juveniles (< 15 mm shell length, sl) through mature, gravid adults (> 80 mm sl). However, no large, old adults (> 110 mm sl) were found. Specimens were morphologically similar to specimens from the central and upper Colorado River drainage of Texas. Other collections made further upstream in Choke Canyon Reservoir and the Frio River up and down-stream of the reservoir, Live Oak and McMullen counties, during 1993 and 1994 period failed to yield any specimens of P. purpuratus. The survey of Lake Corpus Christi by Murray (1978) was made during drought conditions when the water level was extremely low. If present at that time, specimens of P. purpuratus would probably have been found. This suggests an introduction likely occurred in the late 1970s or 1980s.

Several additional bleufer valves were also collected in December 1994 in Amistad Reservoir near the confluence of the Devils River during a drawdown which exposed much of the reservoir bottom. A return trip to the area in January 1995 yielded additional valves as well as three living specimens. These included relatively small juveniles (< 70 mm sl) to larger, older adults (> 125 mm sl). Comparison of the Amistad material to several badly-weathered valves taken by TPWD in January 1992 upstream on the Rio Grande just downstream of San Francisco Creek, Terrell County, indicated the earlier specimens were bleufers as well. Other surveys by TPWD in the Rio Grande down-stream of Amistad Reservoir 1992-1995 failed to yield bleufers. Clearly the Amistad population contained larger, older animals than observed in Lake Corpus Christi. Absence of P. purpuratus in the fossil record (Metcalf 1982) from the Rio Grande drainage suggests the Amistad specimens may also represent an introduction, but at a much earlier date.

Biochemical comparisons. -- Horizontal starch gel electrophoresis (Morizot & Schmidt 1990) was used to examine tissue samples from Rio Grande and Nueces River specimens to confirm identification. Enzyme systems previously found by Neck & Howells (1994) to show differences between P. purpuratus, P. ohiensis (pink papershell), and P. amphichaenus (Texas heelsplitter) were examined. These included glucose-phosphate isomerase (GPI; E.C. 3.1.1), peptidase (PEP; E.C. 3.4.11. or 3.4.13.), superoxide dismutase (SOD; E.C. 2.7.5.1), malate dehydrogenase (MDH; E.C. 1.1.1.37), and phosphoglucomutase (PGM; E.C. 2.7.5.1). Specimens examined included those from Nasworthy Reservoir, Twin Buttes Reservoir, and Middle Concho River (Concho River drainage, Tom Green County); Concho River (Concho County); Mussel Shoal Creek (Trinity River drainage, San Jacinto County); Lake Buchanan (Colorado River drainage, Llano County); Little Brazos River (Brazos River drainage, Robertson County); and B. A. Steinhagen Reservoir (Neches River drainage, Tyler County) as well as specimens from Lake Corpus Christi, Nueces River, and Amistad Reservoir. An additional specimen from the Pascagoula River, Jackson County, Mississippi was also included in the comparison. Specimens of P. ohiensis from Lake Arrowhead (Red River drainage, Clay County) and a P. amphichaenus from B. A. Steinhagen Reservoir were also comparatively examined. No significant electrophoretic differences were found among any of the specimens of P. purpuratus and all were distinctly different from P. ohiensis and P. amphichaenus.

Remarks. -- Commercial shell fishermen (musselers) have reported deliberately transplanting unionids from one body of water to another (Howells 1993) and inadvertent introductions on glochidia-infected fishes may also occur (Neck 1982). Although Potamilus purpuratus is sometimes taken for shells or pearls, harvest for these purposes is generally very minor when compared to that of other commercially more desirable mussels in Texas (Howells 1993). It is possible that the transplanting of pearlproducing Tampico pearlymussels may have inadvertently introduced specimens of P. purpuratus as well because of similarity in appearance of the two species. The only known host fish for the glochidia of P. purpuratus is the freshwater drum (Hoggarth 1992). However, freshwater drum (Aplodinotus grunniens) are rarely stocked as a sport fish or used as live bait. Consequently, introductions by this method appear unlikely.

LITERATURE CITED

Cummings, K. S., & C. A. Mayer. 1993. Field guide to the freshwater mussels of the midwest. Ill. Natur. Hist. Sur., Manual 5, Champaign, 194 pp.

Hoggarth, M. A. 1992. An examination of the glochidia-host relationships reported in the literature for North American species of Unionidae (Mollusca: Bivalvia). Malacology Data Net 3(1-4):1-30.

Howells, R. G. 1993. Preliminary survey of freshwater mussel harvest in Texas. Texas Parks and Wildl. Dept. Management Data Ser. 100, Austin, 30 pp.

Howells, R. G., R. W. Neck & H. D. Murray. 1996. Freshwater mussels of Texas. Texas Parks and Wildlife Press, Austin, 218pp.

Metcalf, A. L. 1982. Fossil unionacean bivalves from three tributaries of the Rio Grande. Pp. 43-59, in Proceedings of the symposium on recent benthological investigations in Texas and adjacent states (J. R. Davis, ed.). Texas Acad. Sci., Austin. 278 pp.

Morizot, D. C., & M. E. Schmidt. 1990. Starch gel electrophoresis and histochemical visualization of proteins. Pp. 23-80, in Electrophoretic and isoelectric focusing techniques in fisheries management (D. H. Whitmore, ed.). CRC Press, Ann Arbor, Michigan. 350 pp.

Murray, H. D. 1978. Freshwater mussels of Lake Corpus Christi, Texas. Bull. Am. Mala. Union 1978:5-6.

Neck, R. W. 1982. A review of interactions between humans and freshwater mussels in Texas. Pp. 169-182, in Proceedings of the symposium on recent benthological investigations in Texas and adjacent states (J. R. Davis, ed.). Texas Acad. Sci., Austin, 278 pp.

Neck, R. W., & R. G. Howells. 1994. Status survey of Texas heelsplitter, Potamilus amphichaenus (Frierson, 1898). Texas Parks Wildl. Dept., Spec. Rept., Austin, 47 pp.

Neck, R. W., & A. L. Metcalf. 1988. Freshwater bivalves of the lower Rio Grande, Texas. Texas J. Sci., 40(3):259-268.

Neves, R. J. 1993. A state-of-the-unionids address. Pages 1-10, in Conservation and management of freshwater mussels (K. S. Cummings, A. C. Buchanan, and L. M. Koch, eds.). Upper Miss. R. Conserv. Comm., St. Louis, Missouri, 189 pp.

Strecker, J. 1931. The distribution of naiades or pearly fresh-water mussels of Texas. Baylor Univ. Mus. Bull. 2, Waco, 69 pp.

Vidrine, M. F. 1993. The historical distributions of freshwater mussels in Louisiana. Gail Q. Vidrine Collectibles, Eunice, Louisiana, 225 pp.

Williams, J. D., M. L. Warren, Jr., K. S. Cummings, J. L. Harris & R. J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries (Bethesda) 18(9):6-22.

Robert G. Howells

Texas parks and Wildlife Department, Heart of the Hills Research Station HC07, Box 62, Ingram, Texas 78025

RGH at: ams@xtc.com
Gale Copyright:
Copyright 1997 Gale, Cengage Learning. All rights reserved.