March 7, 2002 (4:30 PM)

Hays Spring Amphipod

Stygobromus hayi




STATUS: Endangered throughout its range- U.S.A. (DC) (47 FR 5425, February 5, 1982).


SPECIES DESCRIPTION: This small aquatic amphipod is commonly referred to as Washington D.C.'s most famous endemic. The shrimp-like colorless freshwater crustacean is 10 millimeters in length, with eyes lacking and body laterally compressed. The Hays spring amphipod is a detritivore (feeds on organic debris from decomposing plants, animals, and fecal material) (Nature Serve Explorer 2002).


REPRODUCTION AND DEVELOPMENT: Some females have been collected with brood plates, but egg-bearing females have not been found (Nature Serve Explorer 2002).


RANGE AND POPULATION LEVEL: Hays Spring amphipod is only known from one population inhabiting an underground aquifer in an urban area. The animal has been collected from a single spring at the south end of National Zoological Park, Washington, D.C. and at four other locations within Rock Creek Park, which adjoins the National Zoo (Pavek 2002). These three collection sites lie in close proximity to each other. The National Zoological Park spring emerges from the rocky western wall of Rock Creek Valley and flows about 35 m into Rock Creek. The portion of the spring inhabited by Hays Spring amphipod is less than 1 meter wide. The extremely small size of this habitat makes the species exceptionally vulnerable to construction activities, which have drastically reduced the number of springs in Washington (Williams 1977). The size of the population(s) of the crustacean is unknown. Except for the outlet, the aquifer is largely inaccessible. No more than ten individuals have been seen at any one time (Nature Serve Explorer 2002).


HABITAT: The Hays spring amphipod inhabits a ground water outlet that feeds into a low gradient creek. Precise data on this habitat is lacking due to inaccessibility of habitat (Nature Serve Explorer 2002).


PAST THREATS: Survival of this aquatic crustacean has been threatened by modification of its habitat by flooding and construction activities and by over collection for scientific purposes.


Usually high flood levels from Rock Creek reach the level of the spring habitat of Hays Spring amphipod. This level has been flooded with increasing frequency in recent years (CHM Hill 1979). Flood waters may adversely affect the spring habitat by removing individual amphipods, as well as the leaves and soft bottom sediments that form their microhabitat, from the spring.


Construction activities, if not carefully carried out, could adversely affect or eliminate the spring habitat. Such activities have eliminated most of Washingtons springs during the last 100 years (Williams 1977). Although a small fence now surrounds the spring, the significance of this structure could easily be overlooked during parking lot construction. The spring is so small that careless movement of equipment slightly onto the hillside from which the spring flows could have a catastrophic effect on the habitat.


CURRENT THREATS: The small size of the species population and habitat, as well as the fragile nature of the habitat, makes the species vulnerable to flooding, isolated acts of vandalism, and construction or maintenance accidents that might harm or destroy the crustaceans habitat (USFWS 1982). Possible additional threats include groundwater contamination or flow alteration caused by further urban development (Nature Serve Explorer 2002). The urban area surrounding the park poses potential risks due to toxic spills (such as oil and gas), nonpoint source inputs (such as fertilizers and pesticides), land disturbances, sewer leaks, and excessive stormwater flows that might adversely affect groundwater. Except for parklands, additional potential habitat where Hays Spring amphipod populations may have occurred in the District has largely been lost to development (Pavek 2002).







CHZM Hill. 1979. Draft Rock Creek Watershed Conservation Study. Prepared for Department of the Interior, National Park Service.


Nature Serve Explorer. An online encyclopedia of life [web application]. 2001. Version 1.6. Arlington, Virginia, USA: Nature Serve. Available: (Accessed: March 6, 2002).


Pavek, D. 2002. Endemic Amphipods in our Nations Capital. Endangered Species Bulletin. 27 (1): 8-9.


U.S. Fish and Wildlife Service. 1982. Endangered and Threatened Wildlife and Plants; Listing Hays Spring Amphipod as an Endangered Species. 47 Federal Register 5425.


Williams, G. P. 1977. Washington, D.C.s vanishing springs and waterways. Geological Survey Circular 752.