Macroinvertebrates are organisms that lack a backbone and are visible to the naked eye.
In freshwater streams they include insects, crustaceans (crayfish and others), mollusks (clams and mussels), gastropods (snails), oligochaetes (worms) and others.
In most streams and rivers the larval insects dominate the macroinvertebrate community. These organisms are an excellent resource for stream assessment.
The vast majority of stream dwelling macroinvertebrates live in riffle areas. Although riffles in a stream may result from an uneven bedrock bottom or an aggregation of large boulders, the best habitat for macroinvertebrates is riffle composed of moderately-sized rocks ranging in size from 10" cobbles down to 1" gravel.
Riffles composed of smaller material (silt or sand) or much larger rocks provide far fewer living quarters for these organisms. In addition, the constant flow of water provided by riffle areas offers a continuous and plentiful supply of food in the form of plant and animal matter. |