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Benthic Invertebrates

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Benthic Invertebrates

Benthic InvertebrateAlthough the term "benthic invertebrates" is not a familiar one to many people, it represents a life form that is extremely important to fish as a food source. The measurement of benthic invertebrates in aquatic systems is also an important element of the Fish Habitat management System.

One might define benthic invertebrates as "bugs" but that would not be strictly correct. It is more accurate to say that benthic invertebrates are the larvae (most of which live in water, often at the bottom of streams) of insects that live on land in the adult stages of life.

Important species of benthic invertebrates include:

  • Caddisflies
  • Dragonflies
  • Mayflies
  • Stoneflies
  • Blackflies

Caddisfly larvae, Dragonfly, Black fly larvae, adult Caddisfly
Clockwise from top left: Caddisfly larvae,
Dragonfly, Black fly larvae, Adult Caddisfly

The adult insects lay their eggs in aquatic environments. They are capable of rapid re-colonization after a disturbance that affects their aquatic environment, such as drying up of the water body or a flood.

Why are Benthic Invertebrates important to the Fish Habitat Management System?

The System must safeguard the health of aquatic systems and the quality of water, both of which support fish.

Aquatic health and water quality can both be measured through monitoring benthic invertebrates because:

  1. The insect larvae are sensitive to water quality.
  2. The larvae and their adult forms are the key source of food for juvenile salmon as well as adult and juvenile freshwater fish.
  3. The diversity (number of species), abundance (number within each species) and composition of benthic invertebrate populations are relatively constant between areas and seasons, which makes them a good indicator species.

Water quality is high when there are a higher number of species groups which are environmentally-sensitive and important fish food sources.