Functional Feeding Groups

A healthy river has many different invertebrates feeding in many different ways. Diversity is a characteristic of stable, healthy ecosystems. Aquatic invertebrates can be grouped into four functional feeding groups according to how and what they eat:

Scrapers
Scrapers are mainly herbivores (plant-eaters). They remove algae, bacteria and fungus growing on the surface of rocks, twigs and leaf debris. Many of these organisms are flattened to better hang onto rocks while they feed in a current. They feed somewhat like a child licking the icing from the top of a cookie.

Shredders
Shredders are herbivores that chew on coarse leaves and twigs that have started to decay. This group plays an important role in breaking things down to a size that can be handled by other macroinvertebrates.

stonefly nymph

Because these herbivores also consume the nutritious decomposer bacteria and fungi present on the decaying leaves, they are really omnivores. This type of feeding is similar to eating rich peanut butter spread on coarse crackers. Most of the food value is in the spread and not in the cracker!

Collectors
Collectors are omnivores that feed on whatever is easiest to find. They gather fine particles that pass by in lowing water (feces, algae, plant and animal fragments) as well as any bacteria attached to this material.

• Filtering collectors strain particles out of the flowing water with brushes or nets.
• Gathering collectors obtain dead organic material from the river bottom sediments.

Predators
Predators are carnivores that eat small insects, leeches and fish. In turn, these invertebrate predators are often a major food source for other predators such as fish.