Invasive Reeds Reduces Biodiversity

Written by: Chris Borowski-Strategic Watershed Action Team Crew Leader Patricia Huynh-Ontario Provincial Biologist

Does the presence of common reed (Phragmites australis) impact benthic macroinvertebrate communities? We recently wrote about the importance of aquatic invertebrates or what most people would refer to as “bugs.” These invertebrates are also useful indicators of water quality because some are more tolerant of poor water quality and habitat than others. The presence or absence of certain invertebrates provides information about the health of a system.

Phragmites australis, often known as Phragmites or common reed originated from Europe. Common reeds spread quickly through their rich seed-laden heads, rhizomes (roots), and stems, and quickly outcompetes native plants. Phragmites are commonly found along roadside ditches and stormwater management ponds. They create large amounts of biomass as the plants die off, allowing high sediment rates that can impact drainage and dry out wetlands. Their often dense root networks can negatively affect water and invertebrate movement.

Phragmites or common reeds can become dense, making it challenging for wildlife passage.

In the summer of 2021, in collaboration with Bruce Power, Historic Saugeen Métis, and the Invasive Phragmites Control Centre, TUC collected benthic macroinvertebrate samples from a coastal wetland on Lake Huron, in Oliphant, Ontario, to see if there were differences in invertebrate communities between areas of high, medium, and low densities of Phragmites.

The Invasive Phragmites Control Centre often uses manual cutting techniques to remove Phragmites, especially in water. In the background, you can see a large mound of cut Phragmites being taken to shore to be disposed of.

Over the winter months, TUC began the slow process of picking the aquatic invertebrates from the detritus (decaying plant matter) and organic material. This sorting requires using a stereomicroscope to maneuver small invertebrates and other materials under a magnified field. Scuds, aquatic earthworms, mayfly larvae, and midges were some species found among the samples. At the end of sorting and identifying, the team found 34 different types of macroinvertebrates amongst the debris. In general, areas with low or no Phragmites had more organisms per sample, as well as more different types of organisms, compared to samples collected where Phragmites had medium or high density.

TUC staff spent weeks picking through fine sediment and organic matter to sort and identify invertebrates. In total, they counted 8453 invertebrates.

What does this tell us? This indicates that invasive Phragmites are likely to be impacting aquatic invertebrate communities since we saw higher numbers and a wider variety of invertebrates in areas with little or no Phragmites. Aquatic invertebrates are an important source of food for fish. Therefore, the fish are more likely to be found in areas where there are more invertebrates, such as in areas with minimal Phragmites. Our study indicates that these degraded habitats filled with invasive Phragmites may not be suitable for fish since there are fewer sources of food. Removing Phragmites would allow for a more diverse and complex community of plants to grow, supporting a more diverse community of invertebrates, and ultimately a more diverse community of fish.

What can you do to help? Preventing the spread of non-native invasive species is key! When leaving an area containing Phragmites (or other invasive species), make sure your gear and clothes are clean to avoid spreading these intruders. As stewards of the land, we must make a conscious effort to prevent the movement of invasive species so that these ecosystems are still biodiverse for generations to come. 

Want to get involved? Consider becoming a member and volunteering to help us protect, conserve and restore freshwater systems across Canada.