Claws for Alarm
its new environment. For example, the red swamp crawfish is native to the southeastern U.S., including a very small part of Missouri where it plays a natural role in the community. But elsewhere the red swamp crawfish has become one of the most invasive crayfish species in the world.
The same story plays out within state boundaries and with many other crayfish species. Several crayfish species that are native to a particular region of Missouri become invasive when moved to other locations in the state. The White River crawfish, also native to a small part of southeastern Missouri and the Mississippi River, has invaded at least 11 waterways in other parts of the state. Biolo;gists have discovered other species disappear;ing at some of these locations. Species like red swamp crawfish and White River crawfish are hardy and adaptable to a wide variety of con;ditions. Many are aggressive, territorial, and readily reproduce. These traits combined with omnivorous and intense feeding habits make them perfect invaders, suited to overpopulate, out-compete native crayfish and fish species for food and shelter, and alter the ecological balance of their new homes. Though the well-known rusty crayfish is among the most invasive North American crayfish, many other crayfish species possess similar traits and capabilities to extend their range and cause problems.
Our Borders and Beyond
A recent survey of all U.S. state fisheries chiefs found that about half had problems in their states linked to invasive crayfish. Research shows that invasive crayfish cause population declines or elimination of native crayfish species, amphibians, and reptiles. They are also linked with reduced fish abundances and sport fishery declines in streams and lakes. These fish declines occur for several possible reasons. Invasive crayfish alter and destroy habitat, especially aquatic plant beds used by many fish for cover, foraging, spawning, or nursery habitat for young. They often overpopulate and then overgraze fish food such as insects and snails, and insect food such as algae. This leaves less overall food for our prized sport fish.
Invasive crayfish prey on sport fish eggs. They also carry diseases and parasites that could affect many animals. Because crayfish play such a key ecological role, the effects of invasive crayfish reverberate throughout the food chain and often disrupt the way aquatic systems function.
This is not to say that every crayfish invasion will have such dramatic results. Streams and lakes are complicated ecosystems with many