Benthic Macroinvertebrates: Indicators of Environmental Health

Stoneflies are a sensitive group of benthic macroinvertebrates that need cool, clean water to thrive.

Stoneflies are a sensitive group of benthic macroinvertebrates that need cool, clean water to thrive.

The term benthic macroinvertebrates refers to organisms that live at the bottom of streams, rivers, lakes and wetlands. We do a lot of research into these interesting creatures that live in our watershed.

Benthic macroinvertebrates are indicator species. They are kind of like the canary in the coalmine. Looking at their presence, health, numbers and species diversity can tell us a lot about the overall health of a waterbody and the surrounding environment. Abundant, healthy and diverse communities of benthic macroinvertebrates typically indicate healthy water and a thriving local environment. The reverse is also true.

Two dragonfly nymphs caught in the Credit River.
Two dragonfly nymphs caught in the Credit River.

Visible to the naked eye

The term benthic refers to the fact that they’re found at the bottom of a waterbody. They’re called macroinvertebrates because they are big enough to see with the naked eye (macro) and have no backbone (invertebrates). They include insect larvae (e.g. dragonflies; stoneflies), leeches, worms, crustaceans, crayfish, clams, mussels and snails.

They may not have a backbone but that doesn’t mean they’re not tough. Dragonflies, for example, have to adapt to living underwater and above water. Female dragonflies lay their eggs on underwater plants or sometimes directly into the water. The eggs hatch into nymphs that can spend up to four years underwater. Once a nymph is fully grown, it transforms into a dragonfly by crawling out of the water and shedding its skin.

Monitoring their environment

Like humans, benthic macroinvertebrates are influenced by their environment. We monitor the conditions the macroinvertebrates live in by looking at:

  • Rock size, soil and what kind of minerals are found on the bottom of a waterbody
  • How the nearby land is used, including trails, developed areas, construction and recreational activities
  • The presence of vegetation growing alongside streams and rivers
  • Water temperature, ph, oxygen levels, flow and depth

High-tech tools are used to give very accurate readings. A hydrolab MS5  is used to measure oxygen, ph levels and the rate at which heat passes through the water.

CVC staff along the Credit River shoreline getting the hydrolab ready for testing.
CVC staff along the Credit River shoreline getting the hydrolab ready for testing.

We spend about two months each year monitoring over 50 sites throughout the Credit River watershed. Much of the fall and winter are spent in the lab putting all the pieces together. It can take up to two days in the lab to sort through the debris (rocks, sand, plants, etc.), pick out the organisms and correctly identify them.

Once the organisms are identified, we can learn about different aspects of the benthic community at a site. This helps us answer important questions about a site, collaborate with other environmental agencies and track environmental trends over time.

Stoneflies are a sensitive group of benthic macroinvertebrates that need cool, clean water to thrive.
Stoneflies are a sensitive group of benthic macroinvertebrates that need cool, clean water to thrive.

Benthic macroinvertebrates may be small but they’re an important part of the big picture. If you’re interested in learning more about what benthic macroinvertebrates can tell us about the Credit River, check out our latest Integrated Watershed Monitoring Report.

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