Dr. Jay V. Huner, co-author of this article, wades in water covered by duckweed as he stands next to a pyramid trap, used to catch crawfish.

SMALL, HOLLOW CLAY TURRETS, two to ten inches tall and wide, rise from the damp soils. Every southern wetland has them.

Whether the wetland is inundated only when there are heavy, persistent periods of rain or on a regular basis, the turrets will be there - as many as several thousand per acre in wet meadows and one for every foot on either side of roadside ditches.

The natural banks of swamp and marsh pools or man-made levees of rice fields may have a turret every six to twelve inches. They are most conspicuous during the spring rainy season.

So what's beneath the turrets? No, it's not snakes, as so many people believe. It's crawfish. Not just one species, but as many as 150 species from southeastern Texas across the Gulf coastal South to the Atlantic Ocean in the Carolinas and Georgia.

Our own state of Louisiana is home to over 35 species of freshwater crawfish, but twice that many call Georgia their home! At least 20 of Louisiana's crawfish fauna live in wetlands - regions alternately flooded and dried. They range in size from the fully grown one-and-a-half-inch dwarf crawfish to the seven-inch white river crawfish, a true mini-lobster.

Ecologists consider any animal that exerts a significant controlling influence on a specific environment to be a "keystone" species. Crawfish are keystone aquatic invertebrates in wetland environments. They consume huge quantities of animal prey and plant forages. Furthermore, they are able to survive for long periods by consuming decomposing plant material and digesting its living cover of microbes.

While crawfish dominate the flora and fauna "below" them in the hierarchy of the wetland environment, they serve as invaluable conduits of energy to the predatory animals "above" them. Crawfish are major food resources for all manner of carnivorous wetland vertebrates - fish, amphibians, reptiles, birds, and mammals.

Some species specialize in eating seasonally available crawfish. Examples are largemouth bass, Graham's water snakes, bullfrogs, young alligators, yellow-crowned night herons, white ibises, and otters, plus many others.

Less well known to casual observers is the fact that there are many aquatic invertebrate predators - such as giant water bugs, aquatic beetle larvae, dragonfly nymphs, and water spiders that consume large quantities of young crawfish.

A small-mesh pyramid trap,
used for catching small crawfish, can be seen in a wetlands area amid yellow irises.

Nocturnal in nature, crawfish excavate tons of soil in favorable wetland habitats. They are not readily observed, but the chimneys that cap their burrows are obvious.

While the chimneys will certainly erode away during the year, the burrows beneath them will persist while occupied as open macropores, or tunnels, into the earth below. This aerates heavy clay soils and permits movement of surface waters through them.

Of course, this can have its negative impact as well, because waterborne pollutants such as road runoff, pesticides, and oils can penetrate easily into such soils through crawfish burrows, where they are left undetected.

Abandoned burrows are also important because they are muck-filled soil channels that permit other burrowing animals and plant roots to penetrate deep into the subsoil.

Wetlands hold water for periods ranging from a day or two to several months. Various crawfish species are adapted to survive under these different conditions.

Crawfish chimneys are usually found in close proximity to one another. Here they are partially hidden in a wet meadow.

The late Professor Horton H. Hobbs, Jr., a noted astacologist (crawfish biologist), classified crawfish according to the complexities of their burrows and their dependence on them. The three groups of wetland crawfish include primary, secondary, and tertiary burrowers.

The primary burrowers are the moles of the crawfish world, constructing complex burrows. Where water tables are deep, their burrows may extend ten to twelve feet or more in depth, with several different shafts rising to the surface from a more-or-less vertical lower shaft. Where water tables are near the surface, they may construct galleries of burrows parallel to the surface.

The primary burrowers seldom leave burrows and are adapted to burrow life, having large, spade-shaped claws and very small tails. These primary burrowers are most likely to be found in wet meadow habitats where the surface remains dry for long periods. They climb to the surface to feed around the mouths of their burrows during periods of intense rainfall.

In fact, one of the most common species is called the "thunder crawfish" because it is generally seen only when there are heavy thunderstorms in the area.

The secondary burrowers construct less elaborate burrow systems than the primary burrowers do. Two to three shafts rise to the surface from a vertical main shaft. Depth is rarely more than six feet.

These crawfish are much more at ease in surface waters -especially in wet meadows where pools may persist for a week or more before drying-and they are most active at night. Like the primary burrowers, these "chimney crawfish" have spadeshaped claws and small tails.

The tertiary burrowers are familiar to all Louisianians. They are species such as the red swamp crawfish and white river crawfish that spend several months in open water moving in and out of simple burrows with single shafts.

Prolonged stays in burrows involve spawning and incubating of eggs and/or the drying of wetland pools. These burrows are rarely more than three to five feet deep.

The tertiary burrowers have much larger tails in proportion to their bodies than do the primary and secondary burrowers. This is a natural adaptation to living for extended periods in open water, where the rapid flapping of the tail is a survival mechanism to escape from predators.

Louisiana's commercial crawfish industry is worth approximately $50 million annually to farmers and fishermen. It is dependent on two tertiary burrowing species-the red swamp crawfish and the white river crawfish.

About 100 million pounds of these two crawfish species are harvested annually, with about 60 percent coming from the 115,000 to 120,000 acres of crawfish ponds. The remainder are gathered from Louisiana's swamps and marshes, especially the Atchafalaya Basin.

The ponds, swamps, and marshes are all seasonally flooded wetlands, also called short-hydroperiod ecosystems. In fact, the basic pond management strategy simply improves upon the natural hydrological cycle in the region.

In nature, surface waters accumulate in the cool months when precipitation exceeds evaporation. The crawfish emerge with their young. The wetland systems have large quantities of vegetation such as leaves, grasses, and sedges (marsh plants) - that begin to decompose when flooded.

The young crawfish eat seeds; invertebrates that use the microbially enriched plant debris, or detritus, as food; and the debris itself. They grow to harvestable sizes of three to four inches through the winter into the spring. As the marshes and swamps dry in the spring, the crawfish mature, mate, and burrow so that the cycle can repeat itself.

The crawfish farmer controls the timing of pond flooding and draining. He or she controls the forage vegetation base in the pond and manages the water quality with various aeration and management schemes. As a result, many more crawfish are produced than are normally ever produced in natural systems. There may be as much as 3,000 pounds of crawfish per acre, but the average is 500 to 700 pounds per acre.

Crops, especially rice, may be cultivated in the ponds during the summer. As much as 80 to 85 percent of all cultured crawfish is produced in rice/crawfish systems. All crawfish systems, either permanent or rice/crawfish, are especially attractive to water fowl-ducks, coots, and geese and colonial water birds-egrets, herons, ibises, cormorants, gulls, and terns.

In fact, Tulane University ecologists Bruce Heury and Thomas Sherry have documented a direct relationship between the increase in egret, heron, and ibis numbers in Louisiana over the past 20 years and the development of the state's crawfish farming industry.

Dr. Jay V. Huner
is Director of the Crawfish Research Center
at the University of Southwestern Louisiana (USL) in Lafayette.
Dr. Lee Burras is Assistant Professor of Soil Sciences
in the Department of Renewable Resources at USL.

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