Aquatic Macroinvertebrates

Aquatic macroinvertebrates are organisms that spend at least part of their life cycle in water (aquatic), are visible to the naked eye (macro) and have no backbone (invertebrate). They include insects, worms, snails, mussels, leeches, and crayfish. Most live on, under, and around rocks and sediment on the bottom of lakes, rivers and wetlands. These organisms are extremely important to the food chain of aquatic environments as they have an important role in the processing and cycling of nutrients and are major food sources for fish and other aquatic animals.

The aquatic macroinvertebrate community is strongly affected by its environment, including sediment composition and quality, water quality, and hydrological factors that influence the physical habitat. Because the macroinvertebrate community is so dependent on its surroundings, it serves as an effective biological indicator that reflects the overall condition of the aquatic environment. Macroinvertebrates also have low mobility compared to other animals such as fish and birds and are an indicator of local environmental conditions (e.g. particular riffles in streams). Monitoring benthic communities therefore provides a useful assessment of the spatial extent of potential environmental impairments. A further benefit of monitoring aquatic macroinvertebrates relates to their lifespan because they are relatively long lived (1-3 years) and would therefore reflect cumulative environmental impacts.  

There are up to 10,000 species of aquatic macroinvertebrates in stream systems inOntario, each with its own set of environmental tolerances. Some are considered “sensitive,” meaning they can only survive in cool, clean water. When present in large numbers, these macroinvertebrates suggest the stream is in good condition. Others are considered “tolerant,” meaning they can live in water that is warmer and more polluted. An abundance of these organisms suggests environmental conditions have deteriorated. Based on the distribution and abundance of macroinvertebrates, we can learn more about watershed health.

Recent approaches to lake and river health monitoring recognize the importance of physical, chemical and biological interactions.  Adding the biological component to the suite of monitoring activities complements the previous approach by providing an assessment of stream health over a range of conditions as opposed to a spot measurement of water chemistry. It may detect impacts on the aquatic ecosystem that may not be measurable with physical and chemical monitoring alone. 

For identification, images and information pertaining to the numerous aquatic macroinvertebrates across Canada, please refer to the following link:

For more information on aquatic macroinvertebrate monitoring at CVC, including watershed status and trends, please refer to Chapter 15 of the Watershed Health Report:

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