PECK’S CAVE AMPHIPOD } Stygobromus pecki
DESCRIPTION: The Peck’s cave amphipod is a small, aquatic, exclusively subterranean crustacean. Like all members of the genus Stygobromus, this species is eyeless and unpigmented.
HABITAT: The primary habitat of the Peck’s cave amphipod is a zone of permanent darkness in the underground aquifer feeding the springs it has been collected from. This aquifer is characterized by highly varied, below-ground spaces that have been hollowed out within limestone bedrock through dissolution by rainwater. Groundwater is held and conveyed within these hollowed-out spaces, which range in size from honeycomb-like pores to large caverns. The exact depth and subterranean extent of the ranges of the Peck’s cave amphipod have not been determined.
RANGE: This invertebrate is known from the San Antonio segment of the Edwards Aquifer in central Texas. Numerous specimens have been collected at Comal Springs, and a single individual was taken from Hueco Springs in 1992. It is not known whether this species historically ranged in other springs that are now almost perpetually dry, such as San Pedro Springs and San Antonio Springs.
MIGRATION: The Peck’s cave amphipod is not known to migrate.
BREEDING: Nothing is known about the reproductive biology of this particular amphipod. Most other amphipod species produce only a single brood of eggs, which are deposited within a brood pouch on the underside of the female’s body and hatch in one to three weeks.
LIFE CYCLE: The Peck’s cave amphipod’s life history is unknown, but most amphipod species complete their life cycle (from egg to adult) in one year.
FEEDING: The feeding habits of the Peck’s cave amphipod have not been concretely determined, but it is believed to consume both animals and plants, feeding both within the aquifer and on detritus in areas near spring outlets where plant roots interface with spring water.
THREATS: The main threat to the survival of the Peck’s cave amphipod is decreased spring flow due to increased use of groundwater resources throughout the Edwards Aquifer region, which may prove fatal to the species when coupled with periodic drought. Other threats associated with increased urbanization include increased flooding and erosion, pollution, siltation, and storm-water runoff. Exotic species negatively affect the amphipod through competition for food, displacement or destruction of aquatic vegetation, and general habitat degradation.
POPULATION TREND: The Peck’s cave amphipod is currently thought to be confined to small areas surrounding the spring openings of Comal Springs and Hueco Springs and the associated Edwards Aquifer. Numerous specimens have been collected from Comal Springs, and one specimen was collected from Hueco Springs in 1992. Limited data have been collected on the extent to which this species exists below ground.