Amphipod, Illinois cave

Gammarus acherondytes

phylum: Arthropoda

class: Crustacea

order: Amphipoda

family: Gammaridae

status: Endangered, IUCN Endangered, ESA

range: USA (Illinois)

Description and biology

The Illinois cave amphipod is a small freshwater crustacean. It is light blue-gray in color, with small eyes and one long and one shorter antenna. A male Illinois cave amphipod is usually about .8 inch (20 millimeters) long and a female about .5 to .6 inches (12 to 16 millimeters) long. Illinois cave amphipods live in utter darkness in cave streams. They need very cold water and avoid light. They cannot leave their caves, so they will eat any kind of food matter they can find by means of their keen sense of touch, including dead animals, plants, and bacteria.

Illinois cave amphipods are extremely sensitive to pollutants that are introduced into their water supply. The species is an excellent indicator of the quality of the water in the cave systems it inhabits and the groundwater from the surrounding area.

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Because they live underground and away from humans, little is known about the behavior of this species.

Habitat and current distribution

The Illinois cave amphipod lives in karst regions (areas composed of limestone that feature sinkholes, underground streams, and caverns). It is known to occur only in Monroe and St. Clair counties in southwestern Illinois.

History and conservation measures

The Illinois cave amphipod is endemic (native to and occurring only in a particular region) to several cave systems in Monroe and St. Clair counties in southern Illinois. The species was once known to occur in six cave systems, all within a 10-mile radius of Waterloo, Illinois. In 1995, the species was found in only three of these systems, all in Monroe County. This reduction in its range signals a decline in the population of the species.

Groundwater contamination, usually from pesticides used by farmers, is the principal threat to the species. Contamination from human and animal wastes from sewers and septic systems and livestock feedlots in the area also pose a grave danger. The poor water quality, if not corrected, will probably cause the extinction of the species. Sinkholes in the karst region inhabited by the amphipods are sometimes used to dump trash and other pollutants. Because there is no natural filter in a sinkhole to stop the pollutants from reaching the underground waters, the risk of contamination is very high. When amphipods are damaged or killed by the contamination of the streams and groundwater, there is good reason to believe that humans who use the same water sources will be affected as well.

The small range of the Illinois cave amphipod is very close to St. Louis, Missouri, and so the habitat may face further harm from the urban (city; densely populated) environment. The Illinois Department of Natural Resources owns the entrances to two of the three caves known to be Illinois cave amphipod habitats. The entrances to the third cave are privately owned, but have been designated as nature reserves. There are several recovery plans in progress, which include pursuing a better scientific understanding of the species and its habitat needs. The Illinois cave amphipod is currently protected by the Illinois State Endangered Species Protection Act, which prohibits harming or killing it.