University Park, Pa. -- It has been almost 99 years since anyone surveyed crayfish populations in Pennsylvania streams, and nobody really knows if a century of pollution and development has reduced numbers of the pugnacious, clawed invertebrates, or if invasive species are displacing natives.

"Crayfish recently were identified as the second most imperilled aquatic group in North America after mussels," says David Lieb, whose crayfish research in central Pennsylvania streams is part of his pursuit of a doctoral degree in ecology. "Crayfish play a central role in transferring energy up the food chain to fish. They are nocturnal scavengers that eat algae, leaves and smaller invertebrates such as aquatic insects, and turn that into crayfish tissue that is eaten by fish."

Working from Penn State's Pennsylvania Cooperative Fish and Wildlife Research Unit, under the direction of adjunct fisheries professor Robert Carline, Lieb is examining how habitat alterations and exotic species are affecting the state's native species. Lieb also is interested in documenting the functional role of Pennsylvania's native crayfish.

"This is necessary because our understanding of the importance of crayfish is restricted to a handful of species, most of which are native to the Midwest," says Lieb, a native of Hanover, Pa. "Where studied, crayfish are often functionally important, affecting energy flow along multiple pathways and facilitating the transfer of nutrients up through the food chain to commercially and recreationally valuable fish species."

The research is supported by grants from the state's Wild Resources Conservation Fund, the National Park Service and the United States Geologic Survey.

"We know that crayfish are a key player in aquatic systems," Lieb said. "If we lose them, or if they are replaced by an invasive species, we lose a functionally important component of the system and the whole system may be threatened."

Ironically, the species scientists suspect may be pushing native crayfish out of their Pennsylvania habitats, the rusty crayfish from the Midwest, is not as beneficial a food for fish, according to Lieb. "Because of this, it is likely that in systems where our native crayfish are replaced by exotic rusty crayfish, fish populations will suffer," he says. "Rusty crayfish tend to be more aggressive, reclusive and less available to fish."

Lieb's research involves surveying crayfish populations and putting cages into streams -- some with crayfish, some without -- to determine whether crayfish affect other invertebrates such as mayflies, stoneflies and caddisflies. "The results of this study likely will add to the growing body of information that suggests crayfish are functionally important wherever they occur and are deserving of policy directed at their preservation and restoration," he says.

According to Lieb, the role that crayfish play in transferring nutrients up through the food chain to trout and bass is an economically valuable service because streams and rivers attract thousands of fishermen every year.

"These fishermen spend money during their visits, boosting local economies," he says. "Crayfish may benefit local economies by providing forage for recreationally valuable fish species such as trout and bass. The growing realization that crayfish are functionally important but highly vulnerable suggests that future crayfish extirpations and extinctions are likely and that those losses may have far-reaching ecological and economic consequences on our aquatic resources. For this reason, it is vital that natural resource managers and policy-makers recognize the value of native crayfish populations and take measures to preserve them wherever possible."

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