Benthic Invertebrate Workshop

In 3 - Fall, Fauna, Field notes, News, People, Sweetwater Form Nature Reserve, Training & Education by couchiching

Have you ever thought about what a baby mosquito looks like or where a young dragonfly spends its days? For many insects, their story begins underwater. Eggs laid in or near the water hatch, and the larval insect is born into their new watery reality. They find a home amongst the sediment – leaves, wood, sand, pebbles and other debris settled at the bottom of the water. It is here that the young bug will grow, molt, eat, and avoid being eaten. While mosquito larva only takes 4-14 days before they spread their wings and take to the air, larger dragonfly species may spend up to 7 years in their larval form.  

These larval insects, along with other creatures such as leeches, mollusks, and aquatic worms are called benthic macroinvertebrates. They play important roles in the aquatic food webs as detritivores (breaking down organic matter), grazers, predators, and prey for larger wildlife. Different species have evolved to survive in specific conditions, with some being more tolerant to change and pollution than others. Monitoring the composition of benthic macroinvertebrate communities can tell us about water quality, sediment composition, flow regime, and vegetation cover. 

On October 4th, Couchiching Conservancy volunteers and staff went to Sweetwater Nature Reserve for a benthic macroinvertebrate sampling event. The cool waters of the Stickleback Creek emerge from the ground and flow over a stony streambed. This site was selected for the continued and potentially increasing activity from quarries in this area. Before collecting our sample, we recorded various details about the habitat conditions including: 

Bankfull width: hypothetical width of the stream if it were to fill the channel and begin to flow into the floodplain. Comparison to the actual stream width can give you an idea of whether the stream is in a period of drought or flood.  

Canopy cover: percent of the sky above the stream covered by the tree canopy. This is related to the amount of natural light that is able to reach the stream.  

Dissolved oxygen (DO): we used a water quality testing kit to test the amount of oxygen dissolved in the water. Some aquatic organisms such as stoneflies and brook trout require high DO levels to thrive. 

We collected our benthic organism sample following the protocol for a stationary kick test simplified from the 2010 Ontario Stream Assessment Protocol. While one person holds up a square-shaped mesh net another person stands upstream and does the benthic jig – twisting and kicking into the substrate. The sample is transferred to a bucket, producing a “benthic soup” for volunteers to inspect.  

Dorthea and Aiesha doing a benthic kick test at Sedge Wren Marsh in 2015. Photographed by Krystal McLeish. 

We took the sample to our makeshift outdoor laboratory (tables set up in the parking lot). Here, we picked through the sample, using tweezers and eyedroppers to collect organisms and sort them into wells of ice cube trays according to their taxonomic order. It is nearly impossible to identify down to the species level without a microscope and expert identification skills. With the help of hand magnifying lenses, ID guides, and guidance from our benthic experts, we were able to identify 2 mayflies, 13 caddisflies, 2 blood worms, 1 no-see-um, and 1 crane fly. We had 21 bugs too small to categorize with confidence. Before heading home, we returned our sample to the stream.  

What did we learn from our sampling? In our sample, we found many caddisfly larvae. These interesting insects build a protective case around themselves with silk and sediment. This made it difficult to find them in the sample as some just looked like small aggregations of sticks or pebbles. Caddisfly larvae are pollution sensitive, so finding many in our sample is an indicator of healthy water. With a large portion of the sample unidentified, it would not be fair to draw sweeping conclusions based on this data. If you are interested in learning how to use benthic macroinvertebrate data to calculate various ecological metrics, check out this website.   

A big “thank you” to all who attended this event! 

Article by: Aiesha Aggarwal, Conservation Analyst

Video documentary – Jocelyn 

Benthic ID help – Karen, Megan  

Volunteer participants – Jane, Shirley, Glenn, Karen