ABSTRACT
B ENTHIC macroinvertebrates are aquatic organisms without backbones that spend at least a part of their life cycle on the stream bottom. Examples include aquatic insects, such as stoneflies, mayflies, caddisflies, midges, and beetles, as well as crayfish, worms, clams, and snails. Most hatch from eggs and mature from larvae to adults. The majority of the insects spend their larval phase on the river bottom and, after a few weeks to several years, emerge as winged adults. The aquatic beetles, true bugs, and other groups remain in the water as adults. Macroinvertebrates typically collected from the stream substrate are either aquatic larvae or a d ~ 1 t s . l ~ ~
104 BENTHIC MACROINVERTEBRATES
9.2 BENTHIC MACROINVERTEBRATES: INDICATOR ORGANISMS
In practice, stream ecologists observe indicator organisms and their responses (biomonitoring) to determine the quality of the stream environment. There are a number of methods for determining water quality based on biologic characteristics. A wide variety of indicator organisms (biotic groups) is used for biomonitoring. The most often used organisms include algae, bacteria, fish, and macroinvertebrates. A search of the database from 1993 to 1998 carried out by Vesh and Kobzina at the University of California, Berkeley, confirmed that macroinvertebrates are the most popular
Notwithstanding their popularity, in this text, benthic macroinvertebrates are used because they offer a number of advantages:
(1) They are ubiquitous, so they are affected by perturbations in many different habitats.
