Stygobromus hayi

Hay's Spring Amphipod

FWS Focus
Recovery plan for Hay's Spring amphipod

The recovery plan for Hay's Spring amphipod is now available. View the plan on ecos.fws.gov

Overview

Characteristics
Overview

With no eyes or pigmentation, the Hay’s Spring amphipod is a small fresh water crustacean that is built for living life underground. While the species spends most of its life in shallow ground water habitat, it can also be found above ground in seepage springs where the ground water reaches the surface. These springs are generally small wet spots covered by leaf litter and can have little or no flow for much of the year. Very little is known about this species, although it was discovered in 1938. It is one of only two federally listed species within Washington, D.C., found within a small range that includes Rock Creek Park and the National Zoological Park.

Scientific Name

Stygobromus hayi
Common Name
Hay's Spring amphipod
Hay spring stygobromid
FWS Category
Crustaceans
Kingdom

Location in Taxonomic Tree

Identification Numbers

TSN:

Characteristics

Characteristic category

Life Cycle

Characteristics
Life Cycle

Not a great deal is known about the Hay’s Spring amphipod life cycle, but it is presumed that they hatch from eggs and have a brief juvenile stage before becoming adults. In other Stygobromus species, juveniles resemble adults and go through a number of successive molts before becoming mature.

Reproduction

Females of the species contain a brood pouch, which suggests that reproduction occurs via eggs and that females provide some degree of care to the eggs. It is unknown if reproduction is entirely sexual or asexual as well. Males and females have been found during collections, but parthenogenesis, a form of asexual reproduction in which embryos develop without fertilization, is reported in some Stygobromus species. The age and size when individuals become sexually mature is unknown.

Life Span

The lifespan of the Hay’s spring amphipod is unknown, but based on other subterranean amphipod species it is assumed to be 4 to 6 years.

Characteristic category

Habitat

Characteristics
Habitat

The shallow ground water habitats where Hay’s Spring amphipod is found are known as hypotelminorheic, meaning shallow groundwater habitats that are not exposed to light and are vertically isolated from the water table below. These habitats are perched aquifers underlain by a clay layer typically 2 to 20 inches (5 to 50 centimeters) below the surface. They are also high in organic matter. The area where water from these habitats exits to the surface is known as a seepage spring.

Forest cover is an important aspect of the Hay’s spring amphipod habitat. Trees provide food for the species through decaying leaves and organic matter. Tree cover also helps to maintain water quality by filtering out pollutants and keeping water temperatures cool. Spring sites with Stygobromus species have unique water chemistry; compared to other shallow water spring habitats they have higher conductivity and dissolved oxygen and lower pH and temperature. Tree cover also influences the amount of water available for the shallow ground water habitats. Higher amounts of tree cover help to slow down storm water and allow it to infiltrate.

Forest

A dense growth of trees and underbrush covering a large tract.

Cave or Karst

A natural chamber or series of chambers in the earth or in the side of a hill or cliff. An irregular limestone region with sinkholes, underground streams and caverns.

Characteristic category

Food

Characteristics
Food

Although traps containing shrimp have been successful at capturing Hay’s Spring amphipod, the food requirements of the species are currently unknown. Captive specimens of other amphipods in the genus Stygobromus have been observed feeding on protozoans, flatworms, organic debris and plant material.

Characteristic category

Behavior

Characteristics
Behavior

Because the species spends so much of its lifecycle underground, behavior characteristics of the Hay’s Spring amphipod are hard to observe. Other amphipods in the genus Stygobromus use a crawler mobility. It is assumed that the species gets flushed into seepage springs at the surface during high water events, and that it is able to burrow into the clay layer during times where there is low flow in its ground water habitat.

Characteristic category

Physical Characteristics

Characteristics
Size & Shape

The Hay’s Spring amphipod is shaped like a tiny shrimp. Males are slightly larger than females.

MeasurementsMale length: 0.39 inches (9.8 mm)Female length: 0.28 inches (7.0 mm)

Color & Pattern

Hay’s Spring amphipods are modified for life underground and are colorless with no eyes.

Geography

Characteristics
Range

Currently, the entire range of the Hay’s Spring amphipod is limited to 2.5 miles (4.02 km) of the Lower Rock Creek Watershed in Washington, D.C. There are seven known populations of the species. It is assumed that the species is part of a metapopulation, meaning a regional group of connected populations of a species, comprised of populations occurring in several hypotelminorheic habitats. Even if the species isn’t seen at a seepage spring, it may still be present in the ground water habitat below. It is important to protect occupied and unoccupied habitats that are part of the metapopulation.

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