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OBBN training participants collecting benthos from a stream in the Raisin River Watershed.

Little Bugs with a Big Impact

How benthic macroinvertebrates like leeches play an important role in ecosystem management

Many people think that insects are some of the most useless and annoying creatures that exist. But that’s not the case in aquatic ecosystems, where they serve important roles in biomonitoring.

Many people think that insects are some of the most useless and annoying creatures that exist. But that’s not the case in aquatic ecosystems, where they serve important roles in biomonitoring.

Natural water bodies such as lakes, streams and wetlands are habitats for benthos; bottom-dwelling aquatic macroinvertebrates.  Simply put, benthos are the macro animals such as insects, mites, worms, molluscs and crustaceans that live in the water. These creatures can tell us a lot about the health or quality of our natural water bodies. Benthos are considered bioindicators. This means that their functions, population and characteristics can reveal the conditions or health of their surrounding ecosystem. They are abundant and long lived, they respond to changes in water and sediment chemistry, and because of this, they provide early warnings on potential changes in water quality and are very useful in biomonitoring.

Biomonitoring refers to the processes involved in sampling, evaluating and reporting on the condition of an ecosystem using bioindicators. It is important to governments because they use this process to implement legislation and policy such as the EU Water Framework Directive and the US Clean Water Act in order to protect and monitor aquatic life. In Ontario, we have the OBBN or the Ontario Benthic Biomonitoring Network. OBBN is a “collaborative lake, stream and wetland bioassessment network” led by the Ontario Ministry of Environment and Environment Canada and Environment Canada’s Ecological Monitoring and Assessment Network (EMAN).

The OBBN leaders coordinate the 5 components of the program; training, protocol, database management, research and analytical software for hypothesis testing. OBBN also partners with a technical advisory committee which provides technical guidance and review, research, problem solving and program priorities. The University of Waterloo is on the OBBN technical advisory committee, and Faculty of Environment’s Ecology Lab offers OBBN training in Environmental courses. It was through one of my field courses there that I had the opportunity to learn about benthics and  participate in the OBBN certification training program.

Myself and my classmates had to pass a multiple-choice test where we needed to understand OBBN and what they do, know sampling techniques and preservation methods, and correctly identify 40 out of 44 benthos specimens to obtain OBBN certification. During training, we not only learnt how to identify benthic specimens by species, but also how to sample water habitat and assess its biological conditions. We worked in groups to collect water samples and water quality data such as dissolved oxygen levels, turbidity, water temperature and soil particles using a mesh net, and transported it back to the lab. The invertebrates already lodged in the soil sample were taken out, identified under a microscope, tallied and taken back into the lake.

Author Nengi Dublin-Green with classmates collecting benthic samples.

Through our training, we learned how to evaluate aquatic ecosystem health based on benthic species diversities and tolerances. The species of benthic in water depend on various amounts of light, water temperature, oxygen and nutrients, and can help identify the quality of water. There are two classifications of water, lotic and lentic. Lotic describes fast moving, good quality water. It is clear and has a high dissolved oxygen content. The benthic species usually found here are flatworms, aquatic earthworms, midges sow bugs and leeches. These benthic are recognized as flow adapted organisms. Lentic describes slow running, warmer, murkier and poor-quality water. They contain pollution tolerant invertebrates such as mayflies, nymphs, stoneflies, caddisflies and scuds.

I really liked how hands on this program is. Not only did I learn why benthics are important to the environment but I also learnt valuable skills that can be used throughout my career in the future. I am interested in working in Environmental Assessment and benthics are important in carrying out ecosystem assessments, forming policies and making decisions on proposed projects that could potentially alter natural ecosystems.

It’s incredible how important these tiny macroinvertebrates are to the health of aquatic  ecosystems. Most people have no idea what they are, or what their role is in environmental protection and biomonitoring, but these little bugs have far-reaching effects from forming policies and regulations to predicting changes in climate. 

So, next time you see a leech on your leg after a swim in a lake, don’t kill it! It’s a benthic!


Nengi is a fourth year Geography and Environmental Management student at the University of Waterloo. She is a summer intern with A/J