Peck's Cave Amphipod

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Peck's Cave Amphipod

Stygobromus pecki

ListedDecember 18, 1997
FamilyCrangonyctidae (Crustacean)
DescriptionEyeless, unpigmented amphipod.
HabitatUnderground aquifer feeding the springs.
FoodProbably feeds on organic detritus.
ThreatsDecrease in water quantity and quality; groundwater pollution.


Peck's cave amphipod is a subterranean, aquatic crustacean in the family Crangonyctidae. Like all members of the exclusively subterranean genus Stygobromus, this species is eyeless and unpigmented, indicating that its primary habitat is a zone of permanent darkness in the underground aquifer feeding the springs. In 1993, most specimens were collected in drift nets at spring orifices and were found less often downstream, supporting the notion that they are basically defenseless outside the aquifer and have little chance of survival much beyond its confines.

Peck collected the first known specimen of the amphipod later named Stygobromus (=Stygonectes) pecki in his honor at Comal Springs in June 1964. A second specimen was collected at the same place in May 1965. J. R. Holsinger named the species Stygonectes pecki in 1967, selecting the 1965 collection as the type specimen. He later included all the nominal Stygonectes species in the synonymy of the large genus Stygobromus. The U. S. Fish and Wildlife Service has used "cave amphipod" as a generic common name for members of this genus, and this name was simply transliterated as "Peck's cave amphipod" without reference to a particular cave.


Little is known about the behavior of the Peck's cave amphipod. It occurs in a totally dark habitat, and avoids light. It probably feeds on organic detritus, such as dead biomass of plants, animals, and feces.


Its primary habitat is a zone of permanent darkness in the underground aquifer feeding the springs. Individuals are easy prey for predators above ground, so they usually take shelter in crevices in rock and gravel, where they may succeed in reentering the spring orifice.


Over 300 specimens of Peck's cave amphipod have been collected since its description. Most specimens were netted from crevices in rock and gravel near the three largest orifices of Comal Springs on the west side of Landa Park in Comal County, Texas. In 1993 one specimen was collected from a fourth Comal spring run on private property adjacent to Landa Park, and one specimen was collected from Hueco Springs, about 4 mi (6.4 km) north of Comal Springs. Despite extensive collecting efforts, no specimens have been found in other areas of the Edwards Aquifer.


The primary threat to Peck's cave amphipod is a decrease in water quantity and quality as a result of water withdrawal throughout the San Antonio segment of the Edwards Aquifer. Groundwater pollution from human activities also threatens to seriously degrade the water quality of its habitat.

Conservation and Recovery

The Peck's cave amphipod will only survive if its only critical habitat at Comal Springs is protected, and its essential hydrological and water-quality characteristics are conserved. Since the primary threat is associated with the withdrawal of water from the San Antonio segment of the Edwards Aquifer, it is crucial that this hydrological use be limited to an intensity that does not degrade the critical habitat at Comal Springs. The acceptable rate of water use by humans will have to be determined, and will have to account for the effects of periodic drought on groundwater recharge in the region. It will also be necessary to control the risks of local spills of pesticides, hydrocarbon fuels, fertilizers, and other chemicals, any of which could seriously degrade groundwater and damage habitat at Comal Springs. The populations of the Peck's cave amphipod will have to be monitored, and research undertaken into its basic biology and habitat needs.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915

U. S. Fish and Wildlife Service
Ecological Services Field Office
10711 Burnet Road, Suite 200,
Austin, Texas 78758
Telephone: (512) 490-0057
Fax: (512) 490-0974


U. S. Fish and Wildlife Service. 18 December 1997. "Endangered and Threatened Wildlife and Plants: Final Rule To List Three Aquatic Invertebrates in Comal and Hays Counties, TX, as Endangered." Federal Register 62 (243):66295-66304.