What are Freshwater Invertebrates?
Freshwater invertebrates of the southeastern U.S. are invertebrates living in or depending upon the freshwater aquatic environment for some part of their life cycle. Native freshwater invertebrates include crayfish, freshwater mussels, freshwater snails, stoneflies, mayflies, caddisflies, and stygobites (cave-dwelling crustacean invertebrates).

Freshwater invertebrate groups common to North American freshwater aquatic ecosystems are presented below.

Southeastern Species of Greatest Conservation Need Learn more about regional aquatic invertebrate species of greatest conservation need by browsing our species information Web application.

	Arthropods (phylum Arthropoda) Freshwater arthropods include crustaceans such as crayfish, chelicerates such as aquatic mites, and hexapods such as insects.
	Bryozoans (phylum Bryozoa/Ectoprocta and Endoprocta) Bryozoans attach to any non-living material where they use tentacles to capture food from surrounding water.
	Coelenterates (phylum Cnidaria/Coelenterata) Coelenterates include soft-bodied animals such as jellyfish. Primarily marine, coelenterates such as hydras are found in freshwater ecosystems.
	Flatworms (Phylum Platyhelminthes) Flatworms include several worms with flattened bodies such as tapeworms, flukes, and planarians.
	Mollusks (phylum Mollusca) Freshwater mollusks include animals such as freshwater clams (mussels) and freshwater snails.
	Roundworms (phylum Nemata/Nematoda) Freshwater roundworms are characterized by an unsegmented, round body section. They have diverse feeding habits.
	Segmented worms (phylum Annelida) Freshwater segmented worms include aquatic earthworms and leeches, characterized by their segmented body plans.
	Sponges (phylum Porifera) Freshwater sponges live stationary lives and filter water to obtain nutrients.

Ecological Importance of Freshwater Invertebrates
Freshwater invertebrates play several important roles in freshwater ecosystems. They are instrumental in cleaning excess living and nonliving organic material from freshwater systems, a service that contributes to the overall quality of the freshwater resource. Detritivores that feed on decaying organic matter speed up the decomposition process, maintaining the nutrient load in the freshwater resource. Freshwater mussels filter the water on a microscopic level, removing algae, bacteria, and other microorganisms. Altogether, freshwater invertebrates have a tremendous daily impact on the quality of freshwater resources. In addition to this role, freshwater invertebrates are an important reservoir of energy for aquatic ecosystems. When they are consumed by other predators, freshwater invertebrates link nutrients stored in decaying organic material, microorganisms, and other smaller invertebrates to larger organisms, including fish, amphibians, mammals, reptiles, birds, and predatory invertebrates.

Freshwater Invertebrates of the Southeastern United States
The United States has a greater diversity of known aquatic species than any other nation worldwide and much of the nation's freshwater invertebrate diversity is centered in the Southeastern United States. According to U.S. Forest Service figures, the Southeastern United States is home to nearly half of the 11,000 known species of mayflies, stoneflies, caddisflies, dragonflies, and damselflies inhabiting North America north of Mexico (Herrig and Shute, 2002). Among crustaceans such as crayfish, shrimps and scuds, many of the approximately 340 species occur in the Southeastern U.S., and the region is a globally important center of freshwater mollusk diversity including animals such as snails and freshwater clams (mussels). Among the world's freshwater mussels, 91 percent are found in the Southeastern U.S. while more than half of the 516 freshwater snails in North America are found in the Southeastern U.S. (Herrig and Shute, 2002).

For additional Web resources about freshwater invertebrates of the Southeastern U.S., see the "Freshwater Invertebrates Web Resources" page, accessible from the navigation menu at left. NBII Metadata clearinghouse records are also available.

Water quality degradation adversely impacts the health of aquatic communities including fish and invertebrates. For this reason, benthic freshwater invertebrate communities are valuable indicators of water quality because when water quality is reduced, populations of aquatic invertebrates decline in both species diversity and abundance. Monitoring these changes offers a more complete picture than chemical and physical sampling alone because aquatic organisms are continually exposed to water conditions. While chemical and physical sampling methods reflect water quality only at the time of sampling, the long-term presence of aquatic invertebrates with life spans of several months reflects water quality over time (Swarzenski, Mize, and Thompson, 2004 ).

Also, some freshwater invertebrates are more sensitive to water quality changes than others. This can be useful for determining the severity of water quality problems that may be affecting a freshwater resource. When a freshwater resource is degraded, the most sensitive species are lost first, followed by species more tolerant of habitat degradation. Depending on the type and severity of water quality degradation affecting a freshwater ecosystem, additional species become displaced (Chambers and Messinger, 2001).

In particular, mayflies, stoneflies, and caddisfly larvae are sensitive to water quality degradation. When water quality is impaired, populations of these invertebrates can be expected to decline. As a result, special attention is paid to the percentage of mayflies, stoneflies, and caddisflies in freshwater invertebrate samples from an aquatic ecosystem. This percentage is referred to as "EPT," an acronym referring to the taxonomic orders Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies) (Swarzenski et al., 2004).