Macroinvertebrates are the tiny insects that live in streams and are a food source for many fish and other aquatic organisms. Most energy or nutrients are derived outside the water body, and macroinvertebrates collect and convert most of this energy into available forms used by other inhabitants of the stream. Macroinvertebrates are grouped into four â€œfunctional groupsâ€: grazers, shredders, collectors and filter feeders, and predators. Grazers feed on algae that grow on rocks, wood and other streambed materials. Shredders eat the leaves and detritus that fall into the stream, converting the nutrients into energy for other aquatic life such as salmon. Collectors and filter feeders feed on minute particles of organic matter carried in the water column. Predators feed on other aquatic insects.
Macroinvertebrate species differ in their tolerance to pollutants, temperature and other physical and chemical stressors. Therefore monitoring the numbers and diversity of these species can tell resource managers a great deal about the overall health of the stream and indicate trends in ecological conditions. Typical water quality and habitat assessments tell us about conditions in a stream at a point in time. Macroinvertebrates are long-term, relatively immobile inhabitants of streams. This fact, coupled with their predictable responses to environmental changes, make macroinvertebrates good indicators of current and past stream conditions.
Since late summer of 2001, the Environmental Resources staff have been conducting macroinvertebrate assessments on Squalicum, Baker, Whatcom, Padden, Cemetery and Connelly Creeks. The surveys are conducted in late summer, when the diversity of insects reaches a maximum. The assessment follows the protocols developed for the Department of Ecologyâ€™s Benthic Macroinvertebrate Biological Monitoring Protocols for Rivers and Streams (2001). A 2004 Centennial Grant from the Department of Ecology paid Western Washington Universityâ€™s Institute for Watershed Studies to identify and analyze the samples. They produced the Urban Streams Monitoring Program Report (PDF), which was published September, 2006.