2007 SOUTHEASTERN NATURALIST 6(1):141–150 Invasive Crayfish Orconectes neglectus Threatens Native Crayfishes in the Spring River Drainage of Arkansas and Missouri Daniel D. Magoulick1,* and Robert J. DiStefano2 Abstract - Invasive species are one of the major threats to biological diversity. Invasive species of crayfish are known to negatively impact native species in aquatic ecosystems. We recently found that an Ozark endemic crayfish, Orconectes neglectus, has been introduced into the Spring River drainage of southern Missouri and northern Arkansas and appears to have the potential to negatively impact the native communities. We used quantitative kick netting along the Spring River and selected tributaries to determine the distribution and abundance of O. neglectus and its potential to impact native crayfish species. The native crayfishes Orconectes eupunctus, a species of special concern, and Cambarus hubbsi appear to no longer occur throughout much of their former range in the Spring River drainage where O. neglectus is now abundant. Orconectes eupunctus, C. hubbsi, and O. neglectus mainly used fast-flowing riffle and run habitats with a mix of gravel, cobble, and boulder, whereas the other common species collected, Orconectes punctimanus and Orconectes ozarkae, were more generalists in habitat use and were found at all sampled sites. Orconectes eupunctus and C. hubbsi were positively associated with each other, but negatively associated with O. neglectus, despite their similar habitat use. These results provide evidence that O. neglectus is expanding its range, possibly to the detriment of O. eupunctus and C. hubbsi. An intensive field survey and manipulative experiments would be required to confirm the disappearance of the native species, and the mechanisms involved. Introduction Invasive species have been suggested as one of the three major threats to biological diversity, along with habitat loss and fragmentation, and macroscale climatic stresses (Soule and Kohm 1989). Invasive crayfish can negatively impact native crayfishes (Butler and Stein 1985, Hobbs et al. 1989, Momot 1996) and other members of the aquatic community (Gamradt et al. 1997, Olsen et al. 1991). We have found, in the Spring River drainage, an invasive crayfish species, Orconectes neglectus Faxon, that has potential to negatively impact native crayfishes (Flinders and Magoulick 2005). Orconectes eupunctus Williams, listed as imperiled in Missouri and globally (Missouri Natural Heritage Program 2006), and Cambarus hubbsi Creaser, endemic to the Ozarks, were native to the Spring River drainage and abundant at sites on the West Fork of the South Fork (hereafter West 1USGS, Arkansas Cooperative Fish and Wildlife Research Unit, Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701. 2Missouri Department of Conservation, Resource Science Center, Columbia, MO 65201. *Corresponding author - danmag@uark.edu. 142 Southeastern Naturalist Vol. 6, No. 1 Fork) and upper South Fork Spring River (hereafter South Fork) as recently as 1984 (Pflieger 1996). Orconectes neglectus is not native to the Spring River drainage (Pflieger 1996) and was absent from 1984 collections at these sites (W.L. Pflieger, Missouri Department of Conservation, Jefferson City, MO unpubl. data). In 1998, we found established populations of O. neglectus in the West Fork and South Fork, and O. eupunctus and C. hubbsi were absent from sites where they were formerly abundant (Flinders and Magoulick 2005). Orconectes neglectus, native to the White, Arkansas, and Kansas river drainages of the central United States, now occurs in high numbers in the West Fork and extends into the South Fork (Flinders and Magoulick 2005). These results suggest that: 1) O. neglectus was introduced into the West Fork of the Spring River between 1984 and 1998; 2) O. neglectus may be negatively impacting the native crayfish community, especially O. eupunctus; and 3) O. neglectus has the potential to expand its distribution in the Spring River drainage, affecting other species including the imperiled Orconectes marchandi Hobbs (Flinders and Magoulick 2005, Taylor et al. 1996). Crayfish introductions have resulted in drastic changes in aquatic systems, both to native crayfish faunas (Berrill 1985, Capelli and Munjal 1982, Momot 1996) and to other members of the aquatic communities (Gamradt et al. 1997, Olsen et al. 1991), but most of the previously documented invasions have dealt with intercontinental or large-scale interdrainage introductions (Butler and Stein 1985, Hill and Lodge 1994, Soderback 1992). However, crayfish are known to be introduced by smaller scale interdrainage transfers through bait-bucket introduction and other vectors (Riggert et al. 1999). To determine impacts of invasive species on native species, it is important to document the invasion and its extent, and any species displacement, prior to launching studies to determine mechanisms of displacement. The objectives of this study were to determine 1) the distribution and abundance of Orconectes neglectus in the Spring River watershed, 2) associations between O. neglectus and other crayfish species in the South Fork Spring River drainage, and 3) the relative importance of environmental variables to the crayfish community. Methods The study was conducted in the Spring River drainage in north-central Arkansas and south-central Missouri (36°N, 91°W). Located in the Salem Plateau physiographic region of the Ozark Plateaus, the Spring River drains a total area of 3926 km2 from Oregon and Howell counties in south-central Missouri and Fulton, Sharp, Randolph, and Lawrence counties in north-central Arkansas. Geology consists predominantly of medium textured, rapidly permeable dolomites, cherts, and limestone (Adamski et al. 1995) forming a karst landscape with many springs, ranging from small seeps to large sinkholes feeding small intermittent and larger permanent streams. Land use in the Spring 2007 D.D. Magoulick and R.J. DiStefano 143 River drainage is predominantly pasture for livestock and forest land consisting mainly of oak and hickory trees. No major urban areas occur in the drainage. Stream channels generally contain well-defined riffles and pools, with streambeds consisting largely of coarse gravel, cobble, boulder, and bedrock. We sampled sites along the South Fork (8), West Fork (5), and Spring River (8) in 1998, 1999, and 2001 to determine the distribution and relative abundance of O. neglectus in the Spring River watershed. Kick-net sampling was conducted at multiple sites on the South Fork (4 sites on 16–20 June1998 and 8 sites on 21–23 March 2001), West Fork (3 sites on 20–21 June 1998, 3 sites on 22–23 March 1999, and 2 sites on 19–20 March 2001), and Spring River (1 site on 9 July 1998 and 7 sites on 13–14 June 1999). Most sites were sampled on a single date, but 2 sites on the West Fork and 4 sites on the South Fork were sampled in multiple years. Crayfish were collected using a quantitative kick-net method in which organisms were dislodged from a 1-m2 area by thoroughly kicking and disturbing the substrate directly upstream of a 1.5 x 1.0-m seine net (mesh size = 3 mm) (Mather and Stein 1993). Crayfish dislodged from the substrate were washed into the seine net with the aid of the current and by pulling the seine through the sample area. In 1998 and 1999, three to five replicate 1-m2 kick-net samples were collected in each of riffle, run, pool, backwater, and vegetation habitats at each site. Some habitats types were not collected when they were not represented at particular sites. In 2001, 10 to 20 replicate samples were collected in each habitat type for a total of 40 to 70 replicate samples per site at each of 2 sites along the West Fork and 8 sites along the South Fork to better determine the boundary of O. neglectus distribution and species associations. In each sample, we determined densities of all crayfish species, and recorded sex, reproductive status, molting status, and carapace length (to the nearest 0.1 mm) for all individuals. These data allowed us to determine ageclass structure and life-history characteristics of O. neglectus and other common species at these sites. In 1998 and 1999, physical environmental variables (depth, current velocity, and substrate composition) were also measured at each sample location to determine relationships between crayfish densities and environmental variables (Flinders 2000). Habitat use by crayfish can differ with crayfish size (Flinders, and Magoulick 2007, Stein and Magnuson 1976), so specimens of all species collected were classified as either small (carapace length 􀂔 15.0 mm) or large (carapace length > 15.0 mm) and considered as separate species in the analyses. Size-frequency histograms of Spring River crayfish showed crayfish 􀂔 15.0 mm were age 0 and 1. Species associations were determined by detrended correspondence analysis using 1998 and 1999 species densities. The number of kick-net samples collected per site differed between 1998 and 1999, so species associations were determined at the site scale by using the mean relative abundance of species per site in these years. Canonical correspondence analysis and forward selection of environmental variables were used to determine the importance of environmental variables. Species data were log10 (x + 1) transformed prior to analysis. 144 Southeastern Naturalist Vol. 6, No. 1 Results In 2001, O. neglectus were found throughout the West Fork of the Spring River and into portions of the South Fork Spring River (Fig. 1). Orconectes eupunctus and C. hubbsi were not found in the West Fork, but were found in portions of the South Fork, whereas O. ozarkae Williams and O. punctimanus Creaser were found at all sites sampled on the West Fork and South Fork. In 2001, O. neglectus made up a large proportion of the crayfish community in the Figure 1. Sampling sites in 2001 and crayfish species relative abundances along the West Fork and South Fork Spring River in Arkansas and Missouri. 2007 D.D. Magoulick and R.J. DiStefano 145 West Fork and adjacent portions of the South Fork, but decreased in abundance downstream farther from the mouth of the West Fork (Fig. 1). Orconectes ozarkae and O. punctimanus were also relatively abundant in portions of the South Fork drainage, with O. punctimanus being most abundant upstream and O. ozarkae being most abundant downstream (Fig. 1). There was a narrow zone of overlap between O. neglectus and O. eupunctus in the South Fork, but densities of O. eupunctus in these areas were extremely low (Fig. 1). In 1998 and 1999, Orconectes neglectus was negatively associated with O. eupunctus and C. hubbsi, which were positively associated with each other (Fig. 2). Orconectes neglectus was positively associated with the West Fork sites, and O. eupunctus and C. hubbsi were positively associated with Spring River sites (Fig. 2). Cambarus hubbsi, O. eupunctus, and O. neglectus were found most often in fast-flowing riffle and run habitats, whereas O. ozarkae and O. punctimanus were found in a broader range of habitats (Fig. 3). Percent silt, water depth, substrate diversity, and mean current velocity were important abiotic variables related to crayfish species’ relative densities (Table 1). Figure 2. Detrended correspondence analysis ordination showing crayfish speciessize class associations in 1998 and 1999. Species-size classes are triangles. Sites symbols represent West Fork (diamonds), South Fork (squares), and Spring River (circles). Species abbreviations are as follows: OZ = O. ozarkae, PUNCT = O. punctimanus, EUP = O. eupunctus, HUBBS = C. hubbsi, and NEG = O. neglectus. Crayfish were categorized as large (L, > 15 mm carapace length) and small (S, 􀂔 15 mm carapace length). 146 Southeastern Naturalist Vol. 6, No. 1 The four species of Orconectes collected in 2001 overlapped greatly in their size distributions, but O. punctimanus had more large individuals than the other species (Fig. 4). Similar numbers of male (266) and female (258) crayfish were collected in 2001. Ovigerous females of O. ozarkae, O. punctimanus, O. eupunctus, and O. neglectus were collected in March 2001, with egg counts ranging from 150–200 (n = 3), 200–800 (n = 6), 50 (n = 1), and 200 (n = 1), respectively. Discussion Orconectes neglectus is native to the White River and Spring River (Neosho) drainages in the western Ozark region of Arkansas, Missouri, Oklahoma, and Kansas (Pflieger 1996). Orconectes neglectus appears to Figure 3. Mean (± SE) number of crayfish in riffle, run, and pool habitats per site. Table 1. Relative importance of physical habitat variables on relative abundance of crayfish species-size classes in the Spring River drainage in 1998 and 1999 CCA, and forward selection of environmental variables using log10 (x + 0.1) transformed crayfish abundance data. Variable Var. N LambdaA P F Silt 27 0.32 0.005 9.13 Depth 19 0.23 0.005 6.92 Substrate diversity 28 0.08 0.02 2.45 Current velocity 18 0.07 0.025 2.26 Cobble 23 0.05 0.125 1.6 Bedrock 21 0.04 0.35 1.17 Gravel 25 0.01 0.975 0.35 Boulder 22 0.01 0.94 0.32 2007 D.D. Magoulick and R.J. DiStefano 147 have been introduced into the Spring River (Black) drainage of Arkansas and Missouri sometime after 1984 and spread throughout the lower portion of the West Fork and into portions of the South Fork Spring River (􀂧 3 km upstream and 􀂧 10 km downstream from the mouth of West Fork). Our survey was somewhat limited with regard to number of sample sites. However, results indicated that Orconectes eupunctus and Cambarus hubbsi abundances have declined and further suggest that one or both species may have been extirpated from the West Fork during this same time period, as we found none during our collections even though O. eupunctus and C. hubbsi made up a substantial proportion of the crayfish community in the West Fork during 1984 (O. eupunctus 8–33% and C. hubbsi 4–14%; W.L. Pflieger, unpubl. data). Collections made by Pflieger in 1984 in the West Fork yielded no O. neglectus. The sparse overlap of O. neglectus and O. eupunctus and the negative sociation between O. neglectus and both O. eupunctus and C. hubbsi. Indicated that O. neglectus occupied habitats formerly occupied by O. Figure 4. Size-frequency histograms for the four Orconectes species collected in the West Fork and South Fork Spring River during March 2001. 148 Southeastern Naturalist Vol. 6, No. 1 eupunctus and C. hubbsi and possibly displaced these native crayfishes at several sites from the West Fork and portions of the South Fork. A more intensive follow-up survey would be required to confirm the disappearance of O. eupunctus and C. hubbsi from the West Fork. Field and lab experiments and life-history data would be required to determine mechanisms involved in a possible displacement. Interspecific competition is a potential mechanism responsible for the observed declines of O. eupunctus and C. hubbsi by O. neglectus. Rabalais and Magoulick (2006) did field experiments that suggested O. eupunctus were displaced from their former range, but interspecific competition between adult male O. eupunctus and O. neglectus during summer did not appear to be the mechanism responsible. Reproductive interference (Berrill 1985, Perry et al. 2001) and lifehistory differences (Riggert et al. 1999) are also possible explanations for declines of native crayfishes. Butler and Stein (1985) found that native male O. sanbornii Faxon preferentially mated with invasive female O. rusticus Girard, and they suggested that inappropriate mate selection was responsible for reduced recruitment of O. sanbornii. Other possible explanations for declines in abundances of O. eupunctus and C. hubbsi include changes in land use and corresponding changes in stream habitat. Large-scale abiotic changes such as global warming may also impact species distributions and abundances. However, these factors are likely to act at much larger temporal scales than have been observed in the present study. Additionally, Rabalais and Magoulick (2006) found that O. eupunctus could successfully grow and survive in their former range in the West Fork, suggesting that changes in the abiotic environment were not responsible for the decline of O. eupunctus in the West Fork. Orconectes neglectus has also been recently introduced into southeastern New York streams potentially through bait-bucket, pet-trade release, or accidental release during fish stocking (Daniels et al. 2001). The bait-bucket vector is suspected in other crayfish invasions (Lodge et al. 2000) and is also a likely candidate for introduction from the White River to Spring River drainage in the Ozarks. The introduction of O. neglectus within the Ozarks was an example of a small-scale interdrainage introduction that has happened elsewhere in the Ozarks (Riggert et al. 1999). It seems likely that small-scale interdrainage introductions are more common than larger scale interdrainage and intercontinental species introductions. Further study will be needed to address this question. It is not uncommon for invasive crayfish to displace native crayfish (Butler and Stein 1985, Hobbs et al. 1989, Momot 1996). Still, little is known regarding crayfish invasions and mechanisms involved. Important questions that remain to be determined include: how far will the invader travel, can the invasion be controlled, what native species might be displaced, how will the invader displace native species, and what other ecosystem properties will be impacted. Further studies will be required to address these questions. In particular, a follow-up survey and field and laboratory experiments need to be conducted to 2007 D.D. Magoulick and R.J. DiStefano 149 determine species displacement, mechanisms involved, and impacts on ecosystem structure and function. Acknowledgments G. Piercey and C. Flinders provided valuable field assistance. We especially thank the numerous landowners for stream access throughout the course of this study. 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