Benthic means something at or near the bottom of a body of water, macro means large, but not “sea monster” large, and invertebrate means an animal without a backbone or spine. If “benthic macroinvertebrate” were a different language, it could be loosely translated as “water bug”, though that’s only part of the story.

For aquatic ecologists, benthic macroinvertebrates are a window into a watery underworld. Like the world we occupy as humans, the world under water is diverse with vast expanses of bedrock, forests filled with aquatic plants, playgrounds of fallen tree branches, mountains of rocks and soft carpets of last year’s leaves. Through each of these habitats flows the lifeblood that allows this community of bugs to survive—water.

But what happens if we replace some of this water with something else? Perhaps some oil down a storm sewer or a little too much lawn fertilizer applied next to the creek. Would the benthics notice? The simple answer is yes, of course they would notice, just like humans would notice if a factory in their town started pumping out air filled chemicals. At first, we might just grumble to the neighbours about it. Heavy smog and respiratory issues might make the news. We might move away to an area with cleaner air. As time passes, the more sensitive among us might get sick. As it is with humans, so it is with bugs.

Each spring, Conservation Halton ecologists begin the monitoring season by heading out to collect benthic macroinvertebrates  before the larvae have had a chance to emerge as adults. Throughout April and May, the ecologists will visit about 45 sites and collect 300 individual bugs at each site. To do this, an ecologist moves slowly across the creek, from one bank to the other, holding a net in front of them and against the bottom of the creek, shuffling their feet to disturb the top layer of sand, stone or muck. As this material flows into the net, the bugs living within it will flow in too.

Once collected, the contents of the net are placed in a large plastic jar and brought back to the laboratory. The sample is rinsed in a strainer to remove some of the very fine dirt and then scooped, teaspoon by teaspoon, into a tray of water so the bugs can be more easily seen and picked out. From dragonflies to blackflies to leeches to water striders, each bug is counted and placed in a jar of preservative, where it will sit for half the year before being identified with a microscope in the winter months.

Research conducted across North America informs us about the different habitat preferences and pollution tolerances of each benthic we collect, from the highly sensitive stoneflies to the willing-to-live-anywhere midges. The unique benthic communities at each site have a story to tell and this story becomes even more interesting when we return to the same site each year to see if there have been any major shifts in what is living there.

When changes do occur, our ecologists become detectives, looking for clues to understand what might be going on. Was there an increase in sediment after rain caused erosion upstream? Was there an increase or decrease in the predators that rely on benthic macroinvertebrates as food? Is it a response to the low water levels and warm water temperatures seen during a hot dry summer? Maybe there is an increase in algae, indicating a higher amount of nutrients in the stream than usual. More often than not, it will be some combination of factors.

As bottom dwellers, benthic macroinvertebrates are uniquely adapted for their environment and the wide range of materials found in streams. They can dig, cling, crawl and swim, while some like it slow and mucky and others prefer it fast and rocky. The same goes for their food choices, whether it’s hunted down and pounced on or caught in outstretched arms as it floats past. Their little bodies are adapted to their surroundings, so changes to their surroundings will affect their ability to find a home and feed themselves.

Ecosystems are constantly changing, shifting, adapting and reverting, depending on what is moving in and out of them. The reason for changes seen in the benthic community are rarely simple and continued study is needed to understand where a community has been and where it is heading. As climate change increases storm events, changes temperature patterns, affects when creeks freeze over in the winter and thaw in the spring and introduces more invasive species from other parts of the continent, the benthic community will adapt. For some, it will open up new habitats and provide a new niche to occupy. For others, it will likely be a death sentence, with water temperatures warmer than they are able to tolerate. In this way, benthics can act as a red flag when, under what appears to be a babbling brook in a healthy forest, a community is in distress.

However, the news is not all bad. As our understanding of benthics increases, we are able to improve benthic habitat through stewardship and restoration projects and check back to see if these projects are working through sampling and monitoring. It may not be simple or easy but the outcomes of restoring habitat for benthic macroinvertebrates—and all of the other species that depend on them—makes it all worthwhile.

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Last modified: November 29, 2017

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