Freshwater Benthic Macroinvertebrates: what they are, why they’re important & what they can tell us


Freshwater benthic macroinvertebrates, also known as benthos, are ecologically important species to monitor, as they can tell us a lot about the quality of water bodies and the potential effectiveness of restoration efforts. 

What are benthos?

Freshwater benthic macroinvertebrates are bottom-dwelling aquatic invertebrates which include animals such as insects, crustaceans, mollusks, and annelids. They live part or all of their life cycle in water and are often referred to as “benthos” due to their habitat on, in, or near the bottom of water bodies. Benthos play a key role in nutrient cycling in aquatic environments, as they are largely responsible for the movement of organic matter through the aquatic food web. 

Benthos as Bioindicators 

Benthos are incredibly sensitive to their environment, so their presence or absence is a good indicator of water quality. They also cannot escape pollution and may show the cumulative impacts of said pollution in their biology, which makes them excellent bioindicators. In general, water bodies in good condition support an abundant, diverse community of macroinvertebrates, while water bodies in poor condition are populated only by pollution-tolerant species. 

The Ontario Benthic Biomonitoring Network (OBBN) is a biomonitoring network which can evaluate aquatic ecosystem conditions and the effectiveness of conservation and pollution-reduction programs based on the sampling of benthos. Sampling strategies are determined based on the type of water body – whether it’s a stream, wetland, or lake. With more and more stress being put on Canada’s 25 watersheds, monitoring is necessary to track changes and progress in restoration projects. 

New Developments

Lately, new global advances in environmental DNA metabarcoding, or eDNA for short, has shown a lot of potential in detecting environmental stress. It involves taking samples of soil or water and searching for fragments of DNA which are specific to certain species. It also overcomes the shortcomings of the OBBN, both in terms of time and money.

Still, 60 percent of Canada’s sub-watersheds lack adequate data for health indicators – including benthos. Only 43 out of 167 were found to be in good or very good health. eDNA is our hope to help fill in some of the data gaps in monitoring efforts. 

You can learn more about benthos and aquatic benthic macroinvertebrate identification through Ecology Lab workshops and resources.