- Scientific name: Stygobromus tenuis
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Special Concern (MA Endangered Species Act)
Description
Smith, D. G. 1984. Selected freshwater invertebrates proposed for special concern status in Massachusetts, Part II. Mass. Dept. of Env. Qual. Engineering, Div. of Wat. Pollut. Control. Westborough, MA.
The piedmont groundwater amphipod is a laterally compressed, many-segmented, freshwater crustacean that looks like a small, flat shrimp. As with other Stygobromus amphipods, the species is troglomorphic, lacking eyes, pigment, and possessing elongated appendages. Body coloration ranges from whitish, creamy, or straw-colored. Adults in Massachusetts range in size from 5.5-9.5 mm (0.22-0.37 inches; Smith 2000).
The piedmont groundwater amphipod can be confused with the Taconic cave amphipod (Stygobromus borealis), which co-occurs with this species in Massachusetts. The Taconic cave amphipod is the only other subterranean amphipod known from Massachusetts. Identification guides sufficiently illustrate the differences among the species based on adult body length and characteristics of spines found on an appendage of the thoracic segments (Smith 2000).
Life cycle and behavior
Little is known about the life history of this species. Adults are present year-round with females recorded with eggs or brood plates from May to September (Smith 1984). Females produce a few large, ovoid-shaped eggs (Smith 1986).
Distribution and abundance
The piedmont groundwater amphipod ranges from Virginia north to New York and Massachusetts. In Massachusetts, the known range of this species is limited to the Housatonic River watershed, recorded at two sites in the extreme southern Taconic Mountains in southwestern Massachusetts. The status of the piedmont groundwater amphipod population in Massachusetts is uncertain. The karst habitat where it is found is uncommon in Massachusetts. This amphipod is rarely encountered and is listed under the Massachusetts Endangered Species Act as a species of Special Concern. All listed species are protected from killing, collecting, possessing, or sale and from activities that would destroy habitat and thus directly or indirectly cause mortality or disrupt critical behaviors. In addition, listed animals are specifically protected from activities that disrupt nesting, breeding, feeding, or migration.
Habitat
The piedmont groundwater amphipod is a stygobiont, or a subterranean aquatic organism, found in upland karst terrain, which is soluble carbonate bedrock that forms underground networks of caverns and streams. This species is found in springs connected with deep aquifers in the extreme southern Taconic Mountains in southwestern Massachusetts (Smith 1986). This habitat is unlike that described for this species elsewhere in its range (Holsinger 1967, 1978), where it is found in shallow groundwater or hypotelminorheic habitats including wells, seeps, and small springs along the coastal plain.
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Threats
Potential threats to the piedmont groundwater amphipod are groundwater contamination and use. For example, springhouses where rare species have been found are often on private property and subject to owner discretion. If the spring outlets were dammed to create a pond for irrigation, livestock, or aesthetic reasons, this hydrologic alteration could be detrimental. Climate change may pose an additional threat to this species because of potentially reduced groundwater levels.
Conservation
Survey and monitoring
The last targeted survey effort for this species was in the early 1990s. As such, effort is needed to evaluate its historical distribution and persistence in Massachusetts. Surveys should also reserve effort to identify and target potentially suitable habitat in the Housatonic and Hoosic River watersheds. Monitoring efforts are recommended at least every five years or as needed at its historical sites.
Management
Protection of piedmont groundwater amphipod habitat is critical for species persistence in Massachusetts. Since the species’ known distribution is from only a few sites, alteration of groundwater levels, groundwater pollution (e.g., road salts), and spring and seep habitat should be minimized.
Research needs
Surveys should continue to target historical sites but also identify new carbonate rich springs and subterranean habitat to better understand its distribution, relative abundance, and habitat requirements in Massachusetts. Physical surveys coupled with eDNA collections could improve species detection, assuming species DNA markers are developed. Additional genetic analyses can determine where Massachusetts populations place within the Stygobromus tenuis species complex and may further uncover cryptic diversity if historical and new populations are found. Basic life history knowledge of this species in Massachusetts is also limited including longevity and reproductive timing. Further research is also needed to assess piedmont groundwater amphipod habitat and species risk to climate change projections, as these groundwater systems may be impacted by more frequent and prolonged drought.
References
Holsinger, J.R. 1978. Systematics of the subterranean amphipod genus Stygobromus (Crangonyctidae), part II: Species of the eastern United States. Smithsonian Contributions Zoology. No 266. 144 pp.
Holsinger, J.R. 1972. The freshwater amphipod crustaceans (Gammaridae) of North America. In Biota of Freshwater Ecosystems. United States Environmental Protection Agency. Identification Manual 5: 1-89.
Holsinger, J.R. 1967. Systematics, speciation, and the distribution of the subterranean amphipod genus Stygonectes (Gammaridae). Bulletin United States National Museum 259: 1-176.
Smith, D.G. 1984. Selected freshwater invertebrates proposed for special concern status in Massachusetts, Part II. Massachusetts Department of Environmental Quality Engineering, Division of Water Pollution Control, Boston MA.
Smith, D.G. 1986 (1984-1985). The occurrence of the troglobitic amphipod, Stygobromus tenuis tenuis (Smith) (Crangonyctidae) in the Taconic Mountains of southwestern Massachusetts (USA): a case for the existence of a subterranean refugium in a glaciated region. International Journal of Speleology 14: 31-37.
Smith, D.G. 2000. Keys to the Freshwater Macroinvertebrates of southern New England. Published by author. Sunderland, MA. 243 pp.
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| Date published: | March 12, 2025 |
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