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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.
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 - firstname.lastname@example.org.
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.
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
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.
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.
G. Piercey and C. Flinders provided valuable field assistance. We especially
thank the numerous landowners for stream access throughout the course of this
study. We also thank E. Larson and J. Westhoff for comments that improved the
quality of this paper. This research was supported by a grant from the US Fish and
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