Amphipods, also called freshwater shrimp, scuds, or side-swimmers, are small, bottom-dwelling crustaceans that can grow up to 2 centimeters in length. These invertebrates exhibit highly variable coloration, ranging from dark brown and green to white and translucent. Physical differences between Grammarus lacustris and Hyalella Azteca—the most commonly found amphipods in western Minnesota—can be hard to discern in the field, but each species has distinct antennae characteristics that can be identified using a microscope.
Amphipods are found in many of North America's freshwater ecosystems, particularly in shallow lakes and wetlands throughout the prairie pothole region, which extends from central Alberta to Iowa. Researchers suspect amphipods are biological indicators of ecosystem health, and hypothesize that they will thrive with good water quality, abundant aquatic vegetation, and low predator abundance. Because they are unable to disperse by flight, amphipods colonize new basins by spreading through connected waterways or attaching themselves to the plumage of waterfowl.
Amphipods are an important part of prairie wetland food webs, shredding and consuming dead plant matter and algae while simultaneously acting as a significant prey source for ducks, salamanders, water birds, and fish. Amphipods overwinter as adults and pair for mating in late winter or early spring. Fertilized eggs are kept in a brood pouch on the underside of the female's body, and she releases newly hatched amphipods when she molts shortly thereafter. The exact lifespan of these invertebrates is not well documented.
History and Status.
Previous studies suggest that amphipod populations have declined throughout the prairie pothole region. This is potentially the result of several factors, including increases in fish occurrences in the waters where amphipods live and the intensity of agricultural land use across the Midwestern landscape. Because these crustaceans are an important component of many migrating and breeding waterfowl diets, the Minnesota Department of Natural Resources and partners including Bemidji State University are doing research to better understand the habitat conditions sustaining abundant amphipod populations in western Minnesota. Scientists also are assessing the effectiveness of stocking amphipods to revive wildlife habitat. Collectively, the results will help wildlife managers protect and restore remaining prairie wetlands.
Breanna Keith and Jake Carleen,, Bemidji State University graduate research assistants