Benthic Macroinvertebrates are exactly what the name suggests - bottom-dwelling spineless aquatic animals that can be seen with the naked eye. These critters spend at least part of their lives in the water attached to rocks, vegetation, sticks or burrowed into the bottom sediments of freshwater streams, lakes, or ponds. Insects like stoneflies, mayflies and craneflies only spend the larval stage of their life cycle in the water. Some enjoy years in the water to emerge only for a couple of weeks on land as adults. Others spend their whole lives in the water such as amphipods, (scuds), snails and mussels.
Benthic macroinvertebrates (benthos) are excellent water quality indicators and can tell a great deal about the biological condition of a waterbody; the main reason why it is important to evaluate them. Evaluating the abundance and diversity of benthic species is a reliable indicator because they are stationary and sensitive to changes in water quality. Healthy water bodies support a great number and diversity of macroinvertebrates that areboth tolerant and intolerant of pollution. However, samples that contain onlypollution-tolerant species may indicate a problem with water quality.
Benthic monitoring is the study of the ‘bugs in the mud’ and these organisms frame the base of the aquatic food chain. Benthic Monitoring is one component of the Lake System Health program of the Muskoka Water Strategy. The District of Muskoka developed this program to enhance existing Lake Health Monitoring. Lake Vernon presently has three alternating stations that are monitored annually by volunteers in partnership with the District of Muskoka.
Each spring on Lake Vernon, samples are collected by a trained bio-technician in the littoral zone of the lake using the “travelling-kick-and-sweep” method. The littoral zone is where the invertebrates live, such as in the substrate, sediments below the substrate, top of rocks, water’s edge, and on emergent vegetation near the shoreline. Macroinvertebrates have adaptated to live in these microhabitats. Mayfly larva, for example, can crawl over slippery rocks as they eat the attached algae.
After collection, benthos are live counted and identified using the eye, and then released or sometimes they are preserved and sorted in a lab using a microscope. The data gathered from the Lake Vernon sample sites is sent to the Ontario Benthos Biomonitoring Network (OBBN), a large-scale collaborative research initiative led by the Dorset Environmental Science Centre in order to compare and monitor lakes and streams in watersheds across Ontario.
If you would like more information on Benthic Invertebrates, their habitat, or monitoring, please see the following resources.
Muskoka Watershed Council https://www.muskokawatershed.org/