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Invasion of the Upper Susquehanna River Watershed by Rusty Crayfish (Orconectes rusticus)
Mark L. Kuhlmann and Peter D. Hazelton

Northeastern Naturalist, Volume 14, Issue 4 (2007): 507–518

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2007 NORTHEASTERN NATURALIST 14(4):507–518 Invasion of the Upper Susquehanna River Watershed by Rusty Crayfi sh (Orconectes rusticus) Mark L. Kuhlmann1,* and Peter D. Hazelton1,2 Abstract - Orconectes rusticus (rusty crayfish) has spread from its original range throughout much of northeastern North America. Invading rusty crayfish can completely replace native crayfish and impact other parts of the community through changes in consumption, disturbance, and other effects. Our main objectives were to document rusty crayfish distribution in streams of the upper Susquehanna River watershed, NY, and to determine the extent of changes in crayfish community composition since the last major survey. We sampled streams during 1999–2005 to describe the current distribution of crayfish species and to document short-term temporal changes. To determine long-term changes in species composition and distribution, we compared our data to museum specimen collection records. We found significant changes in the crayfish community; our surveys found 2 species not previously reported from the upper Susquehanna River watershed and failed to find 2 species previously reported. We also found that rusty crayfish are widespread in the watershed and continues to expand, while the ranges of native congeners are retracting. Introduction Invasions by nonindigenous species are a significant threat to the diversity and function of communities (Lodge et al. 2000, Mack et al. 2000, Richter et al. 1997). Freshwater communities are especially threatened by invasions because high rates of endemism in certain taxa (e.g., mussels, crayfish) make species with small ranges more vulnerable to extinction (Lodge et al. 1998, Mack et al. 2000). Furthermore, although natural overland dispersal by aquatic species over even short distances is rare, human-assisted dispersal across these barriers can be common, making short-range introductions of species among regional watersheds relatively frequent (Lodge et al. 2000, MacIsaac et al. 2001). Crayfish in particular represent a significant invasion threat to aquatic ecosystems. Often the largest invertebrates in freshwater communities, crayfish play significant roles through the food web, as both consumers and prey, and as agents of disturbance (e.g., bioturbation, macrophyte destruction; reviewed by Momot 1995). Thus, changes in the crayfish community could have large effects on biodiversity, community structure, and ecosystem function (but see Helms and Creed 2005, Nyström and Strand 1996, Nyström et al. 1999). 1Biology Department, Hartwick College, Oneonta, NY 13820. 2Current address - Warnell School of Forest Resources, University of Georgia, Athens, GA 30602. *Corresponding author - kuhlmannm@hartwick.edu. 508 Northeastern Naturalist Vol. 14, No. 4 Orconectes rusticus (Girard) (rusty crayfi sh) is native to the Ohio River drainage, but since at least the 1960s has spread from its original range throughout much of northeastern North America, probably by bait-bucket introductions (Berrill 1978, Butler and Stein 1985, Capelli and Magnuson 1983, Crocker 1979, Gunderson 2002). In some areas (e.g., Wisconsin lakes), O. rusticus often completely replaces native or previously established congeners (Butler and Stein 1985, Lodge et al. 1986, Perry et al. 2001). Invading O. rusticus often attains a higher population density than the species it replaces, and thus can impact the rest of the community through changes in consumption, disturbance, and other effects (Lodge et al. 1985, Olsen et al. 1991, Wilson et al. 2004). Orconectes rusticus was not reported from the upper Susquehanna River watershed in New York at the time of the last description of the region’s crayfish community (Crocker 1957). There are no published accounts of O. rusticus in the region since then, although it has been reported in other New York drainages, including the adjacent Mohawk watershed (Crocker 1979, Daniels 1998). Unpublished reports suggest that O. rusticus became common in Otsego Lake, headwaters of the Susquehanna River, in the early 1970s (Harman 1976, Phillips 1977), but no information is available for the streams. Given O. rusticus’ known ability to invade and displace other crayfish species, our objectives in this study were to document O. rusticus’ distribution in streams of the upper Susquehanna River watershed and to determine the extent of changes in crayfish community composition since the last major survey. We used geographical information from the New York State Museum’s specimen collection database to map the historical distribution of crayfish species in the region, and we conducted semi-quantitative annual sampling of streams to describe the current distribution of crayfish species and to document short-term temporal changes. Methods To determine the historical species composition and distribution of the crayfi sh community, we examined records from the New York State Museum (NYSM) specimen collection. The earliest collections in the NYSM database correspond to those reported by Crocker (1957): specimens from a 1935 stream survey by the New York State Conservation Department and collections made by D.W. Crocker in 1952. The NYSM database includes specifi c locality information for each specimen, not reported in Crocker (1957), so we were able to map the location of earlier collections and compare the historical distribution with the fi ndings of our recent surveys. The NYSM database also includes a small number of collections made after Crocker’s (1957) report. To measure the current distribution of crayfi sh, we conducted rapid, semiquantitative sampling of the upper Susquehanna River watershed annually 2007 M.L. Kuhlmann and P.D. Hazelton 509 during the summers (June–August) of 1999–2005. Our sampling region, centered around Oneonta, NY (42.45°N, 75.08°W), included the Susquehanna River mainstem upstream of Bainbridge, NY, to its headwaters at Otsego Lake and most of the 2nd–3rd order tributaries in the region (Fig. 1). To reduce sampling effort per site to maximize the geographical extent of our study, we focused on a limited range of habitats that were common in all streams in our region, could be sampled rapidly with a standardized protocol, and were most likely to contain crayfi sh: shallow (<0.8 m depth) stream reaches with rocky substrate. These habitat criteria include riffl es and shallow runs but exclude pools, stream reaches with unconsolidated sediments, and deeper portions of the larger rivers. Thus, although our sampling did not include all potential crayfi sh habitats, it allowed us to make within-habitat comparisons among streams within our sampling region. On each stream, 2–7 sites were selected for sampling, largely on the basis of habitat type (see above) and access. Most sampling locations were at bridges or public access points (e.g., parks, fishing access easements), except for a few sites on the Susquehanna River reached by canoe in 2000. Using mostly publicly accessible sites could bias our results (e.g., if nonindigenous species are more likely at sites with easy access). However, data from sites bordered by private property (n = 8, mostly on the Susquehanna River and Charlotte Creek) and from additional intermediate points on Charlotte Creek accessed by canoe in 2006, fit the overall pattern from the other sites, suggesting that the sampled sites were representative of the overall pattern of crayfish distribution. All sites were not sampled every year because of limited time and adverse conditions (e.g., flooding), but at least some sites on 5 of the 8 streams were sampled during at least 4 years (Fig. 1). At each site, we established 3–4 cross-stream transects at 10-m intervals upstream of a starting point selected by blindly tossing a weighted marker. We sampled at 3 points (occasionally fewer if the stream was very narrow) along each transect, haphazardly placed by blindly tossing a weighted marker, but stratifi ed to include both the edge and center of the stream. The maximum water depth we could effectively sample in was about 0.8 m, but summer water levels were typically much shallower. At sites with greater depth (the 2 lower sites on the Unadilla River and the 5–6 lower sites on the Susquehanna River, depending on stream levels), we sampled along transects from one bank out to ≈0.8 m depth. We used 2 main methods to sample crayfi sh: semi-quantitative kicknetting (when current was suffi cient) and quadrat sampling (in slow-moving, shallow water). The modifi ed kicknet (Hauer and Resh 1996), 1 m wide x 1 m tall with a ≈0.5-m bag made of 3-mm mesh, was positioned across the current and held against the substrate with two poles by one person. A second person turned over all rocks and stirred up the substrate in a 0.6-m2 trapezoidal sampling area upstream of the net, allowing the current to carry disturbed crayfi sh into the net. During quadrat sampling, a 1-m2 area was 510 Northeastern Naturalist Vol. 14, No. 4 2007 M.L. Kuhlmann and P.D. Hazelton 511 searched carefully by hand, capturing the crayfi sh in small aquarium nets. During 1999–2004, the number of crayfi sh captured by semi-quantitative methods from 6 sites was low, so we supplemented these samples with collections by hand nets. During June–September 2005, we sampled 11 sites in conjunction with other studies, mostly using non-quantitative methods. All captured crayfi sh were identifi ed in the fi eld to species based on external morphological features (R.A. Daniels, New York State Museum,Albany, NY unpubl. data; Peckarsky et al. 1990). Results Historical distribution Historical records of crayfi sh distribution in the upper Susquehanna watershed are few. Extant records from the 1935 stream survey provide crayfi sh species identifi cation at only six locations: Orconectes immunis (Hagen) (calico crayfi sh) and Orconectes limosus (Rafi nesque) (spinycheek crayfi sh), each at one site (Fig. 1), and Cambarus bartonii (Fabricius) (Appalachian brook crayfi sh) at four sites (all headwater streams not shown on Fig. 1). Crocker (1957) collected crayfi sh at seven locations in 1952: Orconectes propinquus (Girard) (northern clearwater crayfi sh) at three locations, O. limosus at three, O. immunis at one, and C. bartonii at three sites. The next records in the NYSM collection are from 1982: O. propinquus was collected at one and C. bartonii at two sites. A collection from one location on the Susquehanna River in 1991 contained O. rusticus, O. obscurus (Hagen) (Allegheny crayfi sh), and C. bartonii (Fig. 1). Recent distribution During 1999–2005, at a total of 38 locations on the upper Susquehanna River and its tributaries, we captured n >4000 crayfish of four species: O. rusticus, O. propinquus, O. obscurus, and C. bartonii. Cambarus bartonii was primarily found in the upper reaches of the tributaries we sampled (Fig. 1, Table 1), but was also common in small headwater streams (M.L. Kuhlmann, pers. observ.). Orconectes rusticus was by far the most abundant and widely-distributed species, occurring throughout most of the upper Susquehanna River, the upper Unadilla River, and the lower reaches of most other tributaries (Fig. 1, Table 1). The other Orconectes species, O. propinquus and O. obscurus, were most common in the upper reaches of tributaries and were also initially found in a few other locations Figure 1 (opposite page). Map of the upper Susquehanna River watershed study area. North is towards the top in all maps. (A) Locations of specimens in the New York State Museum (NYSM) database (1935–1991). Species and collection date are indicated adjacent to the collection location. Inset (lower right) shows the location of the study area in New York State. (B) Sites sampled (x) during the present study (1999–2005). Numbers in parentheses next to the site symbols indicate the number of sample years. Stream map modifi ed from 3-D Topo Quads, © DeLorme, Yarmouth ME. State map modifi ed from www.netstate.com. 512 Northeastern Naturalist Vol. 14, No. 4 without O. rusticus. Orconectes obscurus was only found in two areas: the upper reaches of Schenevus Creek plus Ouleout Creek and (initially) the Susquehanna River adjacent to the mouth of Ouleout Creek. Orconectes propinquus was found in all other tributaries and at one site on the Susquehanna River (Fig. 1, Table 1). Table 1. Crayfi sh species distribution in streams of the upper Susquehanna River watershed during 1999–2005. Distance upstream measures the stream km from the mouth, except for the Susquehanna River, where distance is measured from Bainbridge, NY, the sampling point farthest downstream. For site locations, see Figure 1-B. • = species present in at least one year. Distance Orconectes O. O. Cambarus Years River upstream (km) rusticus propinquus obscurus bartonii sampled Susquehanna River 0 • • 2 14 • • 6 19 • • 1 24 • 1 32 • 1 46 • 4 48 • 3 85 • 1 Unadilla River Mouth* • • 2 21 • 1 29 • • 2 48 • 1 70 • 1 Butternut Creek 5 • 4 28 • • 4 46 • • 1 Ouleout Creek Mouth* • • 6 1 • • • 6 5 • • • 4 6 • • 1 Otego Creek 1 • 1 12 • • • 1 18 • • • 1 28 • • 1 Charlotte Creek 0 • 5 6 • • • 2 8 • • 6 10 • • 3 15 • • • 1 19 • • • 7 23 • • • 2 25 • • • 6 Schenevus Creek Mouth* • 5 11 • • • 7 14 • • • 4 18 • • • 4 22 • • • • 7 30 • • • 3 Cherry Valley Creek 10 • 1 21 • 1 *Mouth = nearest sampling point on the Susquehanna River. 2007 M.L. Kuhlmann and P.D. Hazelton 513 During our study, we collected O. rusticus at an increasing number of sites. In three of the four tributaries sampled repeatedly, O. rusticus was found at more sites and further upstream after 1999 (Figs. 2A, 2B, and 2C). Butternut Creek, a tributary of the Unadilla River, was the only exception to this pattern; it remained without O. rusticus throughout the sample period (Table 1). In the Susquehanna River, O. rusticus was initially not found at our lower 2 sampling sites, but was collected there by 2005. Simultaneously, we collected O. propinquus at fewer sites in Charlotte Creek and O. obscurus at fewer sites in Schenevus Creek and the Susquehanna River as the study progressed (Figs. 2A, 2B, and 2C). Discussion The crayfi sh community of the upper Susquehanna River watershed has changed considerably over the last 70 years. Our extensive recent sampling, including sites where O. limosus and O.immunis were previously collected, failed to produce those species (Fig. 1). Thus, it is likely that O. limosus and O.immunis are now absent from streams in the region. Because our sampling did not cover deep habitats with slow current, such as pools, it is possible that either of these species persists in those habitats. Additional sampling in these other habitats is necessary to conclusively determine the status of these species in the watershed. Figure 2A. Temporal patterns (1999–2005) of crayfi sh species distribution along Ouleout Creek in the upper Susquehanna River watershed. Distance upstream measures the stream km from the mouth. Symbols indicate sites where a given species was present. When a species was present at more than one site, adjacent points are connected for clarity. If a site was not sampled in a given year, no species has a symbol at that distance. Data for the mouth (plotted at distance = 0 km) are from the nearest sampling point on the Susquehanna River. 514 Northeastern Naturalist Vol. 14, No. 4 We found two crayfi sh species not reported in the upper Susquehanna River watershed prior to 1991: O. obscurus and O. rusticus. The current disjunct distribution of O. obscurus is suggestive of multiple recent introductions, perhaps from adjacent watersheds where it occurs (Crocker 1979, Daniels 1998). However, O. obscurus occurs in lower parts of the Susquehanna River watershed (Crocker 1957), so its presence in the upper watershed did not necessarily result from human introduction. Since none of the streams where O. obscurus occurs were sampled before 1991, it is possible that it was simply missed in earlier surveys. Given its presence in other parts of the Susquehanna River watershed and the paucity of historical samples in our study area, we tentatively classify O. obscurus as native. Orconectes rusticus is clearly a recent introduction. Its distribution and pattern of expansion (Table 1; Figs. 2A, 2B, and 2C) suggest at least two separate points of introduction: the headwaters of the Susquehanna River, possibly one of the lakes, and the upper Unadilla River. As its population Figure 2B. Temporal patterns (1999–2005) of crayfi sh species distribution along Schenevus Creek in the upper Susquehanna River watershed. Distance upstream measures the stream km from the mouth. Symbols indicate sites where a given species was present. When a species was present at more than one site, adjacent points are connected for clarity. If a site was not sampled in a given year, no species has a symbol at that distance. Data for the mouth (plotted at distance = 0 km) are from the nearest sampling point on the Susquehanna River. 2007 M.L. Kuhlmann and P.D. Hazelton 515 appears to expand, O. rusticus may be replacing the native (or previously established) congeners O. propinquus and O. obscurus in some locations. Cambarus bartonii is typically associated with headwater streams (Crocker 1957), although it was collected at numerous locations in the larger streams of the upper Susquehanna River watershed in the past (Fig. 1), implying that it was fairly common there. In contrast, we found C. bartonii at relatively few sites, all in the upper reaches of the streams we sampled. We cannot determine a cause for this apparent change in distribution. It seems unlikely that the invasion of O. rusticus was the direct cause, since C. bartonii and O. rusticus overlap little now. Cambarus bartonii is most common in small headwater streams, which in this area typically lack other crayfi sh (M.L. Kuhlmann, pers. observ.), so it will likely persist in those habitats. Comparisons between our recent sampling and earlier surveys indicate that the crayfi sh community in the upper Susquehanna River watershed has changed greatly over the past 70 years, with the apparent loss of 2 species, the addition of 1 or possibly 2 species, and apparent changes in the distribution of others. The apparent contractions of the ranges of O. propinquus and O. obscurus might be related to the expansion of the introduced species Figure 2C. Temporal patterns (1999–2005) of crayfi sh species distribution along Charlotte Creek in the upper Susquehanna River watershed. Distance upstream measures the stream km from the mouth. Symbols indicate sites where a given species was present. When a species was present at more than one site, adjacent points are connected for clarity. If a site was not sampled in a given year, no species has a symbol at that distance. 516 Northeastern Naturalist Vol. 14, No. 4 O. rusticus. Unfortunately, the lack of data between 1952 and 1999 make it impossible to determine the cause of the apparent loss of O. limosus and O. immunis and the decline of C. bartonii in larger streams. During our sampling, we noted that O. rusticus seems to achieve a much higher population density than the other crayfi sh species in the watershed. For example, at sites with only O. rusticus, median estimated density was 7.6 individuals/m2 with a maximum of >19 individuals/m2. In comparison, O. propinquus had a median estimated density of only 1.8 individuals/m2 when by itself, with a density of >5 individuals/m2 in only two samples. Since O. rusticus occurs primarily in the Susquehanna River and the lower reaches of tributary creeks (Table 1; Figs. 2A, 2B, and 2C), it is possible that this is a result of differences between the habitats where each species is found rather than differences between the species. Unfortunately, we do not have a suffi cient number of observations at sites where the transition from native to introduced species occurred to completely rule out this possibility. However, this apparent pattern of higher O. rusticus density is consistent with what has been reported from other areas O. rusticus has invaded (Lodge et al. 1985, Wilson et al. 2004). Because crayfish have significant roles in stream communities as consumers and agents of disturbance, an increase in crayfish density as a result of the invasion by O. rusticus should have important direct and indirect effects on many parts of the stream community (Momot 1995, Statzner et al. 2000, Usio and Townsend 2004, Zhang et al. 2004). O. rusticus has higher per-gram consumption rates of invertebrates and plants than O. propinquus (Olsen et al. 1991), making the impact of the invasion even greater. As generalist omnivores, crayfish can have direct consumptive effects on a wide range of species, including snails, aquatic insects, macroalgae, and diatoms, which may cascade through the food web to indirectly affect many more species. Through disturbance (e.g., bioturbation), they act as ecosystem engineers and have additional indirect effects (Creed and Reed 2004, Crooks 2002, Jones et al. 1994, Statzner et al. 2000, Usio and Townsend 2004, Zhang et al. 2004). Thus, if low densities of O. propinquus and O. obscurus are replaced by higher densities of invading O. rusticus, we would expect widespread effects on many parts of the upper Susquehanna River watershed community. Acknowledgments We thank J. Sullivan, A. Prisciondaro, M. Irland, G. Hamilton, and S. Caldwell for help in the fi eld and R. Daniels for providing the NYSM specimen data, confi rming species identifi cations, and helpful suggestions. The staff of Hartwick College’s Pine Lake Environmental Center provided logistical support. This manuscript was greatly improved by comments from R. Daniels, P. Fauth, members of the Grossman Lab at the University of Georgia, R. DiStefano, and 3 anonymous reviewers. Partial support for this research came from the Faculty Research Grants Program and a Wandersee Scholar-in-Residence award, both from Hartwick College. 2007 M.L. Kuhlmann and P.D. Hazelton 517 Literature Cited Berrill, M. 1978. 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