Crayfish play important roles in aquatic and
terrestrial ecosystems, both as food sources for many animals and as consumers
of plant and animal material. Crayfish are
linked directly and indirectly to the ecosystems in which they live. Because they are
omnivorous (i.e., consume both plant and animal food, living or dead), and
because they are consumed by animals from various trophic levels, crayfish form
multiple links in aquatic and terrestrial food webs (Lodge et al. 1994, Charlebois and Lamberti 1996, Nystrom et al. 1996). Thus, crayfish are involved in the transfer
of large amounts of energy in these systems. Crayfish process nutrients and make
them available to other animals by (1) breaking down large material via
shredding into smaller sizes, and (2) converting nutrients into biomass. Crayfish feed on aquatic vegetation (e.g.,
macrophytes, algae, and periphyton), macroinvertebrates (e.g., aquatic insects,
mollusks, small crustaceans), and small vertebrates (e.g., amphibians,
small/juvenile fish). Crayfish also
consume nonliving organic matter such as leaf litter or terrestrial animal
carcasses from the riparian zone or shore and decaying aquatic plant and animal
matter (Lodge and Hill 1994). Crayfish
in turn are consumed by invertebrates (including other crayfish), fish, amphibians, reptiles, birds, and mammals (Lodge and
Hill 1994). Crayfish perform an important role as a member of symbiosis
with many invertebrates and as host to various aquatic parasites (Lodge and Hill 1994).
Crayfish also experience competition, both between species and
among different sizes of individuals within a population (Lodge and Hill
1994).
Despite the magnitude of their ecological roles, we have much to learn about crayfish distributions, life histories, and taxonomy. In the United States and Canada, approximately 350 taxa of crayfish are recognized (Taylor et al. 1996, J.E. Cooper, pers. comm.). However, many species still await description (J.E. Cooper, pers. comm.). For example, several current species are now recognized to be species complexes consisting of more than a single taxon. The greatest diversity of crayfishes occurs in the Southeast (Hobbs III 1991, Taylor et al. 1996), and North Carolina harbors at least 37 (possibly up to 46) native and 3 introduced species of Cambarus, Procambarus, Orconectes, and Fallicambarus (Cooper and Braswell 1995, J.E. Cooper, pers. comm.). Many of these species have naturally small native ranges and are therefore vulnerable to environmental change. About half of the described crayfishes in North Carolina are of undetermined conservation status due to a deficiency of data on the distribution and abundance of these animals. Additionally, there are perhaps as many as a dozen native species yet to be described (J.E. Cooper, pers. comm.). Of those species for which we have at least some information, the Scientific Council on Freshwater and Terrestrial Crustaceans suggests that 8 species be listed as significantly rare (suggested state special concern), and that 13 species be put on a watch list (Clamp 1999). These species and 3 newly described species (1 proposed special concern and 2 proposed watch list) are listed accordingly by the North Carolina Natural Heritage Program (LeGrand et al. 2001). Thus, at least 67% of the crayfishes occurring in North Carolina may need some form of protection. Other species have either recently been described or are currently under investigation, and it is too early to say whether these species should also be awarded protective status. New information about current distributions has recently been reported (Cooper and Braswell 1995, Cooper et al. 1998). Yet there are still many geographical gaps across the state where surveys have either not been conducted at all, or not thoroughly or recently. The proposed listing of certain crayfishes by the Scientific Council on Freshwater and Terrestrial Crustaceans (Clamp 1999) is a first step; the authors admit that these decisions have been made based on limited data and that more extensive surveys may provide new information that could alter the conservation of any of these species.
Because we have limited historical
data with which to compare current distributions, it is hard to determine
whether land-use practices and other effects of human actions (e.g.,
introductions of nonindigenous crayfishes) have negatively affected the
crayfish in North Carolina. However,
crayfish can be affected by both water and habitat quality. Changes in water quality that interfere with
respiration (e.g., drastic temperature changes, acidification, pollution) can
be detrimental to crayfish populations.
Many crayfish are oxygen regulators and can survive changes in oxygen
levels (Reiber 1995), but some are oxygen conformers and are less likely to
successfully contend with these changes (Hobbs III 1991). Water pollution, caused by sources such as
sewage, agricultural and urban runoff, acidification, and auto exhaust, can
result in bioaccumulation of pesticides and trace heavy metals (e.g., lead,
copper, and cadmium). This can harm
animals that consume crayfish in addition to directly causing negative effects
on crayfish (e.g., mutation, reproductive failure, death) (Taylor et al. 1995,
Daveikis and Alikham 1996, Anderson et al. 1997, Zaranko et al. 1997). Habitat destruction also can negatively
affect crayfish populations. Land use
practices (e.g., agriculture, logging, and development) can alter habitat
resulting in fewer areas available as shelter to crayfish (Smith et al. 1996,
Richter et al. 1997). For example,
siltation and runoff can decrease macrophyte (a source of food and shelter)
availability, and channelization can alter streambed sculpture. The introduction of non-indigenous
crayfishes to areas currently occupied by native crayfish can result in
competition or even extirpation of natives and can have impacts on other
components of the ecosystem (e.g., fishes, amphibians, macroinvertebrates,
macrophytes, and algae) (Charlebois and Lamberti 1996, Perry
1998, Lodge et al. 2000a).
Nonindigenous crayfishes can affect natives via competition, predation,
genetic dilution, and by serving as disease vectors. Further, introductions of nonindigenous crayfishes can enhance
the negative effects of environmental change on native species because
non-natives are often more tolerant to environmental degradation. Lodge et al. (2000a) consider nonindigenous
crayfish introductions to be the single greatest threat to native crayfish biodiversity
worldwide. In Europe, nonindigenous
crayfishes have contributed to serious declines and even local extinctions of
its 5 native species. In several areas
of North America, combinations of environmental degradation and introductions
of non-native crayfishes have led to declines in native species, and to the
extinction of at least one native crayfish in northern California (Lodge et al.
2000a). During recent decades, at least 3 exotic crayfish species have been
introduced into North Carolina; therefore, we are concerned about potential
impacts to our ecosystems and native crayfish species. Based on species-specific hydrologic basin
distributions and what is known about habitat preferences of native crayfishes,
it may be possible to correlate crayfish distributions with anthropogenic
activities affecting water and stream quality.
Much of our information about the current status of crayfishes in North Carolina comes from previous surveys. Many of these surveys for crayfish were conducted as parts of larger inventories for multiple types of animals (e.g., State Parks, Game Lands, and county inventories conducted by NC Wildlife Resources Commission personnel; surveys for amphibians conducted by NC State Museum of Natural Sciences personnel; basin-wide water quality surveys conducted by Division of Water Quality personnel). Since the proposed project will be taxa specific, we should increase the quality of knowledge relative to (1) quantification, (2) substantial life history and ecology information, (3) seasonality, and (4) sufficient data on burrowing crayfish. Given that undescribed species exist and that we have much to learn about the distributions of crayfishes in North Carolina, it is imperative that we continue to improve our knowledge of crayfish by filling in the distributional gaps with further inventories.