Oct. 10, 2001 COLLEGE STATION, - Crayfish boils may be the delicacy of choice at some Southern dinner parties, but environmental studies indicate there's something else cooking in the lobster-like crustacean's future.
And understanding the ecological recipe may help researchers predict the health of our nation's streams.
Of the nearly 340 species of crayfish in North America, more than half are suffering in some way: 65 are endangered, 45 are threatened and 50 are of "special concern," or on watch for changes in their populations.
At least one researcher at Texas A&M University has set out to understand why, but she's not just looking at the animal itself.
"I'm a community ecologist," said Dr. Fran Gelwick, wildlife and fisheries biologist. "I look at everything that pertains to the health of the environment in which an animal lives. By understanding how organisms influence their environment, as well as how environmental changes affect the organisms, we can monitor for symptoms of adverse conditions."
The findings of Gelwick and graduate student Brian Healy, presented at the recent North American Benthological Society meeting, detailed how crayfish cope with the challenges of weather, predators and human intervention, for example.
"The various species have different strategies, in the evolutionary sense, of dealing with situations," Gelwick said. "Each has their own strength and weakness, but those with the better match to the river system are more likely to sustain their population."
The decline of certain species of crayfish is not unlike that of other wildlife, Gelwick said. Many species of crayfish have a limited natural range (they can't travel too far from water), their habitat is being lost to urban encroachment, and chemical runoff has polluted many water systems.
Yet crayfish play an important role in streams. They eat small fish and insects, process debris and are prey themselves for larger fish and people. These roles are important in maintaining healthy ecosystems, Gelwick said.
"They process large pieces of organic matter," she said. "My idea of dirt might be another animal's idea of food. The crayfish take large leaves, algae or dead animals in a stream and process it into smaller pieces that then can be used by the smaller animals in the ecosystem. You can think of them as a conveyor belt through which a product goes in one way and comes out another that is more useful to the next consumer in the food web."
Crayfish also could be thought of as residential developers - living in self-dug burrows for a while before digging a new place.
"Some animals actually live with crayfish and others use the old burrow left behind," she noted..
For the study, Gelwick and Healy pegged the headwaters of the San Jacinto River, an 85-mile body of water that courses through the Sam Houston National Forest, from Walker County southeast, until pouring into the Gulf of Mexico at Galveston.
They looked at how environmental factors in streams with different flow regimes related to crayfish distribution and, how the crayfish species present fared in response to environmental conditions, such as drought and amongst their competitors and predators.
More than 100 observations were made in pools and runs along the river through the forest. The streams were measured for water speed and depth. The effects of other variables such as water quality, frequency of drought and abundance of predatory fish were compared to the abundance and body size of each crayfish species during the four seasons of one year.
Their findings indicate that drought hammers some kinds of crayfish, predators grab others, while one - Procambarus clarkii - is a generalist who can tolerate such pressures for a better chance of survival, mainly because it not only digs burrows but also can spawn repeatedly during a season.
Here are some factors about the species they observed:
* P. clarkii population - not currently threatened or endangered.
* Orconectes palmeri - not currently threatened or endangered; appears to move, rather than burrow during drought; has larger "pincers" and body size which make it a good competitor and help it avoid predators.
* Procambarus kensleyi - currently is considered of special concern by the Endangered Species Committee of the American Fisheries Society. Gelwick and Healy found its ability to burrow likely makes it more tolerant of drought, but due to its smaller size, it is apparently less competitive with other crayfishes and more susceptible to predators.
Gelwick has been involved with biodiversity research along the Trinity and San Jacinto rivers for about six years in cooperation with the Texas Parks and Wildlife Department and the U.S. Forest Service, which have funded many of her studies.
"We've built up a nice database from the San Jacinto River drainage basin, and those who manage natural and human systems have started talking to each other," Gelwick said. "Together we can help people enjoy their natural resources, while preserving them for generations yet to come"
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