A survey of freshwater mussels (Unionidae) of the Old Sabine Wildlife Management Area, Smith County, Texas.
Riverine mussels have historically dominated aquatic systems of the southeastern United States and their biomass in undisturbed rivers can exceed all other benthos by an order of magnitude (Strayer et al. 1994). They often occur in dense multispecies beds and perform significant functional roles such as removing suspended organic material, moving sediments and providing habitat for other invertebrates (Strayer et al. 1999; Vaughn & Hakenkamp 2001). The mussels of the family Uniondae of the United States are highly speciose with over 300 species known (Neves 1993). However, North American mussel populations have been declining for over a century with 35 species now presumed extinct and more than 40% imperiled to some degree (Neves et al. 1997; Vaughn 1997; Brown & Banks 2001). For many states, the extent of declines for specific species is simply not known (Bogan 1993; Layzer et al. 1993; Neves 1993). Over harvesting, pollution, reservoirs and other human activities have been implicated in mussel losses elsewhere and are certainly issues for this fauna in Texas (Shannon et al. 1993; Howells et al. 1996; Howells 1997).
Texas has over fifty species of unionid mussels in multiple river basins that often have isolated drainage into the Gulf of Mexico (Howells et al. 1996). Consequently, species composition in eastern Texas differs from that of central and western areas (Neck 1982). Water pollution has long impacted the freshwater fauna of east Texas (Shira 1913; Howells 1997). Further, 31 reservoirs have been constructed on its rivers over the years and the change dams cause to water flow downstream is known to have major impacts on mussel diversity and abundance (Vaughn & Taylor 1999; Howells et al. 2000). In addition, erosion from agricultural land and commercial harvesting of mussels have also impacted the freshwater mussels of this area (Neck 1986; Howells 1997). Yet almost no studies on the mussels of the river basins in eastern Texas have been conducted (Howells 1997; Bordelon & Harrel 2004). For example, the upper stretches of the Sabine River have been intensely fished by commercial musselers (Howells 1993; Howells et al. 1996) but the only published surveys of the mussels of this drainage are for Lake Tawakoni (Neck 1986), a Master's thesis written in 1940 (Bechtel 1940) and in-house Texas Parks and Wildlife Department (TPWD) reports summarized in Howells (1997).
The Sabine River arises in the eastern part of north-central Texas (Hunt, Collin, and Rockwall counties), flows southeastward through eastern Texas for approximately 890 km and terminates at Sabine Lake, an estuary of the Gulf of Mexico. The TPWD 's Old Sabine Bottom Wildlife Management Area (OSBWMA) is located 109 km south of Lake Tawakoni in Smith County, Texas and receives flow from both the Sabine River and Lake Fork Creek. The OSBWMA is 2318 hectares of mostly bottomland, hardwood forest along 38 km of the southern bank of the Sabine River. Eighteen km of an old channel of the Sabine River forms much of the southern boundary of the area. The Sabine River at this site has a fall of 0.2 m per km, an average depth of less than 1 m and a flow averaging less than 5 CMS in the summer and 2 m and less than 115 CMS in the winter. Bank erosion exists in the area even though the river along this stretch is forested by the management area on the south and The Little Sandy Hunting Club, an extremely natural bottomland that is in a U. S. Conservation easement, located on its northeastern end.
The "Old Channel" is a smaller cut-off section of the Sabine River running somewhat parallel for 22 km. It meanders through the southern boundary of the OSBWMA for 18 km with a total fall of 0.2 m per km. It is structurally complex with numerous oxbows that may be up to 2.5 m in depth and narrow riffles that can be very shallow. The river feeds the Old Channel when the river level reaches 3.6 m and flow is approximately 28 CMS at the Mineola gauging station. It is also fed by 5 large creeks and several springs so that it flows even during lower water levels. The average summer flow of the Old Channel where it crosses the main road into the OSBWMA is 0.7 CMS and in winter it averages 2.3 CMS.
The substrate in the river consists of sand and clay with large areas of silt and detritus. The Old Channel has less silt but organic debris trapped by fallen trees is extensive in some areas. Although the banks of both the river and channel are lined with typical bottomland trees the waterways should receive some additional improvement over time as a 230 hectare pasture upstream acquired by TPWD in 2003 returns to native vegetation. This project provides a preliminary survey of the mussel fauna of the OSBWMA for future monitoring of species diversity and relative abundances.
Sampling techniques. -- Nine sites on the river and nine sites on the Old Channel were surveyed between June and September 2005. The waterway was first explored for shells and stream characteristics that were appropriate for mussels and when a site was located a timed hand search was initiated (Vaughn et al. 1997). A 40-m stretch was divided into 10 m sections and two persons searched the substrate for mussels for 15 to 20 minutes in each section. Both live and dead mussels were collected, identified and measured (shell length, width and height in mm), with one voucher of each species sent to the Stephen F. Austin State University invertebrate collection. Any questionable specimens were sent to Robert Howells of TPWD for identification.
Data analysis. -- The general recommendations of Krebs (1998) were followed for measuring aspects of diversity. A Shannon-Wiener species diversity (H' base e) and evenness (J') were calculated for each waterway and the rarefaction method (James & Rathbun 1981) was used to calculate the expected number of species at comparable sample sizes. A Jaccard's coefficient of community was used to compare species similarity between watercourses (Brower et al. 1997).
RESULTS AND DISCUSSION
A total of 477 individuals of 17 species was found during approximately 40 person-hours of sampling of the 18 sites (Table 1). Measurements of these 17 species of Unionids are given in Table 2. Three additional species were found at the OSBWMA during other surveys. A sampling during a mark-recapture study at site 5 in the Old Channel recorded one tapered pondhorn, Uniomerus declivis and one pond mussel, Ligumia subrostrata. A large number of pond mussels, was also found in one oxbow pool off the Old Channel. Valves of two flat floaters, Anodonta suborbiculata were found on the river but not at a sample site. The diversity indices for the Sabine River and the Old Channel were not significantly different (Old Channel richness adjusted to the sample size of the river = 13.15; 95% confidence limits of 12-14). However, differences in the species composing the assemblages were evident (C[C.sub.J] = 58.8%) and abundances for species in common were often different (Fig. 1). The river had half the total individuals found in the Old Channel and over 75% of those recorded were dead. Over half of those in the Old Channel were collected alive. The most obvious environmental difference between the river and the Old Channel was the erosion of the steep riverbanks. The banks of the Old Channel were less elevated and often were forested up to the water's edge. Although some silting was evident, erosion was restricted to shorter stretches of the waterway.
Abundances of all mussels were much lower than in comparable surveys in other east Texas rivers (Howells et al. 2000; Bordelon & Harrel 2004). The major substrates of the waterways of the OSBWMA are sand and clay, neither of which are excellent habitats for unionids. However, it is useful to discuss the abundances of each species relative to others in the two habitats with suggestions as to factors that may be involved in the numbers recorded.
Abundant species. -- Four species were found in at least five of the samples in the Sabine River (Table 1). Yellow sandshell, Lampsilis teres, was present at eight of the nine river sites. However, it was even more common in the Old Channel (all nine samples, Fig. 1). Interestingly, a large percentage of the individuals in the Old Channel were recently dead. This species is susceptible to drought conditions (Howells et al. 1996) but even individuals found underwater were often dead. The valves were nearly always of large adults so possibly the high number was the result of natural senescence in this fast growing species (Howells et al. 1996). Washboard, Megalonaias nervosa, was also abundant in the river but never found alive. Erosion of the riverbanks was common in all sites and often the valves of this species were found buried. Some live individuals have been found in nearby sections of the Sabine River, but our data suggests the species may be extirpated in the river bordering the OSBWMA. Fragile papershell, Leptodea fragilis, was found in most sites in both the river and the Old Channel and this may be because it is a species that can tolerate silting (Buchanan 1980). Bleufer, Potamilus purpuratus, was found in five sites on the river and most of these were live specimens. This species was also relatively abundant in the Old Channel with 14 live specimens recorded. Several other species were found in at least five sites in the Old Channel including Louisiana fatmucket, Lampsilis hydiana, and bankclimber, Plectomerus dombeyanus, which were rare in the river (Fig. 1). Additionally, giant floater, Pyganodon grandis; southern mapleleaf, Quadrula apiculata; western pimpleback, Q. mortoni; and pistolgrip, Q. (=Tritogonia) verrucosa, were each found in two or three sites in the river (Table 1).
[FIGURE 1 OMITTED]
Uncommon species. -- Eight species were found in less than five sites in both habitats. This includes threeridge, Amblema plicata, which was only found dead in three sites on the river. This species was once abundant enough in the Sabine River to support a commercial harvest (Howells et al. 1996), and overharvesting may have caused its apparent decline. Rock-pocketbook, Arcidens confragosus, was found in small numbers in both the river and the channel. This species is not rare in eastern Texas but is generally found in limited numbers where it occurs (Howells et al. 1996). Threehorn wartyback, Obliquaria reflexa, was only found in two sites in the river of which one had six individuals and deertoe, Truncilla truncata, was only found in three sites in the river. These two species were abundant in other nearby sites on the river. Texas lilliput, Toxolasma texasensis: pondhorn, Uniomerus tetralasmus: and little spectaclecase, Villosa lienosa, were only found in the Old Channel. Little spectaclecase was found in three sites while only one Texas lilliput and three pondhorns at one site were found. The latter species is known to occur in large numbers in ponds (Howells et al. 1996) and a pool isolated off the Old Channel did have a large number of pondhorns.
In this study, 58% of the species of mussels previously recorded in the Sabine River were found. This suggests the waters bordering and within the OSBWMA support a diverse bivalve fauna. However, some other studies of mussels in east Texas rivers have samples much higher than in this report and other sites on the Sabine River outside the OSBWMA had much higher densities of unionids. None of the species recorded in either of these habitats appeared to be abundant and the lack of optimal substrate is likely the main cause. However, anthropogenic impacts that are known to affect freshwater mussels are evident in the area, such as sand and silt deposition from upstream, and erosion of banks. In addition, during this very dry summer, damage to the banks and substrate of the channel from wild hogs was evident. The waterways of the OSBWMA go through bottomland forest habitat and the impacts of agriculture should be limited. It would be useful to monitor recruitment of young in the unionid fauna at the OSBWMA to determine if individual species are recovering or declining.
The authors thank Texas Parks and Wildlife Department for permission to work on the OSBWMA. We thank Robert G. Howells and Lyubov E. Burlakova for confirming species identifications and Robert Howells, Kevin Herriman and Shaun Crook for reviewing drafts of this manuscript. Voucher specimens have been deposited at the Stephan F. Austin State University invertebrate collection. The Ed and Mary Heath Foundation and the Rosa May Griffin Foundation helped with travel expenses.
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Neil B. Ford and Melissa L. Nicholson
Department of Biology
University of Texas at Tyler
Tyler, Texas 75799
Table 1. Number of living/dead individuals of mussel species collected at sites in the Sabine River and Old Channel and at the Old Sabine Bottom Wildlife Management Area, Smith County, Texas. Sabine River Site Species 1 2 3 4 5 6 7 8 Amblema plicata 0/0 0/0 0/1 0/0 0/1 0/2 0/0 0/0 Arcidens confragosus 0/0 0/0 0/0 0/0 1/0 0/0 0/0 0/0 Lampsilis hydiana 0/0 0/0 0/1 0/0 0/0 0/0 0/0 0/0 Lampsilis teres 0/1 0/1 0/0 1/0 1/1 0/1 0/1 3/2 Leptodea fragilis 2/1 0/2 0/1 1/5 0/1 0/4 1/1 0/0 Megalonaias nervosa 0/7 0/1 0/22 0/25 0/17 0/9 0/4 0/1 Obliquaria reflexa 0/0 0/0 0/0 0/0 0/0 6/0 1/0 0/0 Plectomerus dombeyanus 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Potamilus purpuratus 0/0 0/0 1/0 2/0 0/0 2/0 0/0 0/1 Pyganodon grandis 0/0 0/0 0/0 0/0 0/4 1/0 0/0 0/0 Quadrula apiculata 0/0 0/0 0/0 2/1 0/0 0/2 0/0 0/0 Quadrula mortoni 0/0 0/0 0/0 0/0 0/3 0/5 0/1 0/0 Quadrula verrucosa 0/0 1/0 0/0 0/0 0/2 0/0 0/0 0/0 Toxolasma texasensis 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Truncilla truncata 0/0 0/0 0/0 1/0 0/0 2/0 0/0 2/0 Uniomerus tetralasmus 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Villosa lienosa 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Total abundance (live/dead) Species richness Shannon Diversity index (In) Evenness Sabine River Site Species 9 Totals No. sites present Amblema plicata 0/0 0/4 3 Arcidens confragosus 0/0 1/0 1 Lampsilis hydiana 0/0 0/1 1 Lampsilis teres 0/2 5/9 8 Leptodea fragilis 0/3 4/18 8 Megalonaias nervosa 0/0 0/86 8 Obliquaria reflexa 0/0 7/0 2 Plectomerus dombeyanus 0/0 0/0 0 Potamilus purpuratus 1/0 6/1 5 Pyganodon grandis 0/0 1/4 2 Quadrula apiculata 1/0 3/3 3 Quadrula mortoni 0/0 0/9 3 Quadrula verrucosa 0/0 1/2 2 Toxolasma texasensis 0/0 0/0 0 Truncilla truncata 0/0 5/0 3 Uniomerus tetralasmus 0/0 0/0 0 Villosa lienosa 0/0 0/0 0 Total abundance (live/dead) 33/137 Species richness 13 Shannon Diversity index (ln) 1.78 Evenness 0.69 Old Channel Sites Species 1 2 3 4 5 6 7 Amblema plicata 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Arcidens confragosus 1/0 0/0 0/0 0/0 0/0 0/0 0/1 Lampsilis hydiana 3/4 0/2 3/0 0/0 1/0 4/0 1/0 Lampsilis teres 4/15 0/2 0/4 23/5 7/8 5/1 5/27 Leptodea fragilis 0/2 0/0 0/1 0/3 1/3 2/0 0/1 Megalonaias nervosa 0/0 0/0 0/0 0/0 0/0 0/0 0/2 Obliquaria reflexa 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Plectomerus dombeyanus 10/3 0/2 11/1 4/0 0/1 0/0 7/2 Potamilus purpuratus 0/0 0/0 0/1 9/3 3/1 0/0 1/1 Pyganodon grandis 0/0 0/0 0/0 0/0 0/1 0/1 0/2 Quadrula apiculata 6/0 1/0 4/0 4/0 1/0 0/0 4/0 Quadrula mortoni 1/0 0/0 2/0 0/0 0/2 0/0 0/2 Quadrula verrucosa 3/0 2/2 3/0 6/2 0/0 0/0 0/1 Toxolasma texasensis 0/0 0/0 0/0 0/0 0/1 0/0 0/0 Truncilla truncata 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Uniomerus tetralasmus 0/0 0/0 0/0 0/0 0/0 0/0 0/0 Villosa lienosa 0/0 0/2 0/0 0/2 0/1 0/0 0/0 Total abundance (live/dead) Species richness Shannon diversity index Evenness Old Channel Sites Species 8 9 Totals No. sites present Amblema plicata 0/0 0/0 0/0 0 Arcidens confragosus 0/1 0/0 1/2 3 Lampsilis hydiana 0/0 0/0 12/6 6 Lampsilis teres 5/14 5/5 54/81 9 Leptodea fragilis 1/1 0/2 4/13 8 Megalonaias nervosa 0/0 0/0 0/2 1 Obliquaria reflexa 0/0 0/0 0/0 0 Plectomerus dombeyanus 0/0 2/0 34/9 7 Potamilus purpuratus 1/1 0/0 14/7 5 Pyganodon grandis 0/1 0/5 0/10 5 Quadrula apiculata 1/0 0/0 21/0 7 Quadrula mortoni 0/0 0/1 3/5 5 Quadrula verrucosa 1/0 0/0 15/5 6 Toxolasma texasensis 0/0 0/0 0/1 1 Truncilla truncata 0/0 0/0 0/0 0 Uniomerus tetralasmus 0/0 1/2 1/2 1 Villosa lienosa 0/0 0/0 0/5 3 Total abundance (live/dead) 159/148 Species richness 14 Shannon diversity index 1.92 Evenness 0.73 Table 2. Measurements of Unionid mussels collected at the Old Sabine Wildlife Management Area. Mean [+ or -] SD (minimum-maximum). Species Length (mm) Width (mm) Amblema plicala 76.3 [+ or -] 9.2 59.5 [+ or -] 63.5 (63-83) (51-66) Arcidens confragosus 93.0 [+ or -] 34.1 69.3 [+ or -] 20.9 (57-139) (45-96) Lampsilis hydiana 63.7 [+ or -] 15.3 40.2 [+ or -] 9.8 (34-87) (21-54) Lampsilis teres 94.1 [+ or -] 20.1 44.4 [+ or -] 9.2 (15-124) (10-63) Leptodea fragilis 85.4 [+ or -] 17.6 53.0 [+ or -] 10.9 (47-122) (27-72) Megalonaias nervosa 160.5 [+ or -] 43 106.3 [+ or -] 29.5 (68-220) (44-158) Obliquaria reflexa 37.9 [+ or -] 6.5 30.4 [+ or -] 7.0 (28-45) (20-39) Plectomerus dombeyanus 91.6 [+ or -] 14.9 60.9 [+ or -] 11.8 (47-120) (27-84) Potamilus purpuratus 90.4 [+ or -] 36.0 58.3 [+ or -] 23.2 (45-166) (27-100) Pyganodon grandis 89.3 [+ or -] 15.9 53.7 [+ or -] 9.1 (566-122) (39-68) Quadrula apiculala 54.3 [+ or -] 8.3 45.7 [+ or -] 7.4 (37-71) (28-56) Quadrula mortoni 52.6 [+ or -] 9.8 43.9 [+ or -] 7.7 (22-64) (19-52) Quadrula (=Tritogonia) 109.2 [+ or -] 25.5 62.9 [+ or -] 12.5 verrucosa (50-142) (28-97) Toxolasma texasensis 33.0 1.7 Truncilla truncala 35.6 [+ or -] 12.6 29.6 [+ or -] 7.7 (20-49) (18-38) Uniomerus tetralasmus 91.0 [+ or -] 4.6 46.0 [+ or -] 1.7 (87-96) (45-48) Villosa lienosa 55.8 [+ or -] 10.7 31.8 [+ or -] 6.2 (42-66) (24-40) Species Height (mm) Amblema plicala 38.3 [+ or -] 58.0 (32-46) Arcidens confragosus 59.8 [+ or -] 53.4 (22-139) Lampsilis hydiana 29.3 [+ or -] 9.2 (12-42) Lampsilis teres 31.0 [+ or -] 8.3 (2.0-47) Leptodea fragilis 31.1 [+ or -] 6.5 (18-43) Megalonaias nervosa 69.7 [+ or -] 23.3 (27-101) Obliquaria reflexa 16.3 [+ or -] 3.6 (10-21) Plectomerus dombeyanus 35.5 [+ or -] 16.0 (13-101) Potamilus purpuratus 39.7 [+ or -] 18.5 (16-75) Pyganodon grandis 41.4 [+ or -] 7.0 (25-45) Quadrula apiculala 28.6 [+ or -] 5.8 (19-48) Quadrula mortoni 32.1 [+ or -] 7.1 (11-39) Quadrula (=Tritogonia) 34.7 [+ or -] 10.2 verrucosa (12-32) Toxolasma texasensis 1.2 Truncilla truncala 19.4 [+ or -] 4.6 (12-24) Uniomerus tetralasmus 29.3 [+ or -] 2.3 (28-32) Villosa lienosa 19.0 [+ or -] 5.2 (12-24)
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|Author:||Ford, Neil B.; Nicholson, Melissa L.|
|Publication:||The Texas Journal of Science|
|Date:||Aug 1, 2006|
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