‘Drei-seen-id’ all before: Zebra mussel monitoring

By Daniel Weller

The invasion of zebra mussels (Dreissena polymorpha) in Lake Superior is very much a case of “we’ve seen it all before.” In an effort to better understand where and how zebra mussels are spreading, Parks Canada staff at Lake Superior National Marine Conservation Area (NMCA) and Pukaskwa National Park piloted a monitoring program over the summer of 2020.

Invasive species in the Great Lakes are nothing new. From the spread of sea lamprey through the Great Lakes in the early 1900s to more recent threats like Asian carps, there has been a long line of invasive species entering the Great Lakes. They have caused headaches (at best!) for the people that live, work, and play here, as well as for the creatures that call these lakes home. From a management perspective, Lake Superior has some obvious advantages with respect to aquatic invasive species. At the top of the Great Lakes network, it is often the last for invasive species to reach, and its cold waters aren’t particularly hospitable. Unfortunately, invasive species still find their way into Lake Superior.

Invasive zebra mussels are part of a group called Dreissenids, and they can have wide-ranging, significant impacts on everything from boating and beaches to entire ecosystems. They have been in Lake Superior since the 1980s, and the cold waters of the lake were thought to keep zebra mussel populations restricted to major ports, like Thunder Bay and Duluth. Unfortunately, zebra mussels now appear to be spreading through much of Lake Superior, albeit more slowly than in the other Great Lakes.

The monitoring program ran from June to September at Lake Superior NMCA and Pukaskwa. In collaboration with the Upper Great Lakes Management Unit (Ontario Ministry of Natural Resources and Forestry), mussel samplers were deployed to assess the distribution of zebra mussels across the north shore, including the Pukaskwa coast, Rossport, Nipigon, Red Rock, and Black Bay. The samplers were a set of stacked, square plates suspended above the lakebed and marked by white and red buoys. Zebra Mussels reproduce during the summer months and the offspring, called veligers, drift in the water column until settling on a suitable surface. The sampling plates provide a surface for veligers to colonize that can easily be recovered and assessed. No zebra mussels were confirmed this summer, but certain problems were encountered, including loss of some samplers and uncertainty of identification on others. Overall the results of this pilot project were inconclusive. We will be considering ways to improve monitoring in future.

Currently, there aren’t many options for controlling zebra mussels once they establish in a waterbody. Knowing how far they have spread is a key first step in trying to address the problem, and preventing further spread. If you are moving a boat or other gear between waterbodies, please remember to ‘CLEAN. DRAIN. DRY.’ A little prevention goes a long way!