Why are macroinvertebrates important to stream health

In particular, mayflies Ephemeroptera , stoneflies Plecoptera and caddisflies Trichoptera are the most sensitive to changes in water quality. The second group are macroinvertebrates that are moderately tolerant of pollution. Included in this group are:. Macroinvertebrate indices are commonly used to analyze the health of freshwater streams.

The scoring criteria are based on the streams in a particular region. They include collecting a subsample of macroinvertebrates and tallying the various taxa. A numerical value is calculated to provide a criterion Excellent, Good, Fair, or Poor to describe the biological integrity of the stream. Streams with excellent water quality will have macroinvertebrates present from all three groups.

Severely impacted streams will only have pollution tolerant macroinvertebrates. In addition to their use as bioindicators, macroinvertebrates are also important components of the stream food web. They are grouped according to their primary food source as shredders, collectors, grazers scrapers or predators.

Shredders feed on larger pieces of organic matter such as leaves and woody debris. They include stoneflies Figure 4 and some species of caddisflies.

Collectors, such as blackflies and clams, gather or filter small organic particulates in the water column or along the bottom. Grazers or scrapers , such as mayflies and some caddisflies, feed on detritus, algae and aquatic plants. Predators are macroinvertebrates that only feed on animal tissue. Some of the most voracious predators along the bottom of a stream include hellgrammites and dragonfly nymphs. Hellgrammites have strong mandibles that they use to capture and tear apart their prey Figure 5.

Dragonflies are the most effective predators in the animal kingdom. The nymphs typically prey on insect larvae and worms but larger species will even feed on small fish and tadpoles Figure 6.

After leaving the water and emerging as an adult, dragonflies feed primarily on mosquitoes and flies. Macroinvertebrates are also an important food source for many stream fish species, including trout. In coldwater streams around the world, trout are popular game fish amongst anglers. Benthic macroinvertebrates are commonly used as indicators of the biological condition of waterbodies. They are reliable indicators because they spend all or most of their lives in water, are easy to collect and differ in their tolerance to pollution.

Macroinvertebrates respond to human disturbance in fairly predictable ways, are relatively easy to identify in the laboratory, often live for more than a year and, unlike fish, have limited mobility. In fact, because they cannot escape pollution, macroinvertebrates have the capacity to integrate the effects of the stressors to which they are exposed, in combination and over time. Biologists have been studying the health and composition of benthic macroinvertebrate communities for decades.

Evaluating the abundance and variety of benthic macroinvertebrates in a waterbody gives us an indication of the biological condition of that waterbody. Generally, waterbodies in healthy biological condition support a wide variety and high number of macroinvertebrate taxa, including many that are intolerant of pollution.

Caddisfly — There are many different families of caddisflies, some of which would be classified as pollution-sensitive.

The caddisflies found in Arlington are moderately pollution-sensitive. Mayfly — There are many families of mayflies, many of which are classified as pollution-sensitive. Organisms that can survive in poor water quality. They often have adaptations that allow them to survive in water with low dissolved oxygen, turbid waters or nutrient-enriched waters. If the stream was restored, we would hope to see more pollution-sensitive and tolerant macroinvertebrates living there.

Every day, macroinvertebrates are surrounded by water and any pollutants that may be in the water. If pollutants were in the water last week or yesterday, the quantity and diversity of macroinvertebrates present would reflect this in the water quality.