What do Zebra Mussels Mean for Western Provinces?

In October 2013 provincial water quality experts were in for a shock. Despite years of public education campaigns and boater check stops, it happened. The first zebra mussel was reported on a boat being pulled from Lake Winnipeg. Rapid response surveys were launched, and adult mussels were found in four harbours in the southern basin and a small private dock. In the spring of 2014, liquid potash was added to the harbours (mussels at the private dock occurred in a shallow channel that froze to the bottom) in an attempt to eradicate the species from the lake and provide time for provincial officials to initiate a “stop/slow the spread” campaign. While the potash treatment did eradicate the mussels from the harbours, they were quickly re-invaded. Zebra mussels have now been found throughout the southern basin, near Georges Island in Lake Winnipeg’s north basin and in Cedar Lake, which is connected to the north basin at Grand Rapids, MB.

Zebra mussels are listed in the top 100 worst invasive species by the International Union for the Conservation of Nature (IUCN), and for good reason. Their ability to rapidly spread between lakes and rivers has been well documented in North America. The United States Geological Survey (USGS) has an excellent time series of maps showing just how quickly this species can spread. The impact of zebra mussels on lake and river ecosystems has been documented in over 1,000 scientific publications, including a number of quantitative reviews. These studies demonstrate the remarkable ability of a single species to alter a wide variety of physical and chemical variables, and affect nearly every species in the food web. These studies also reveal that the impacts of zebra mussels were highly variable. For example, phytoplankton, which are floating microscopic algae that the mussels eat, were reduced by approximately 50 per cent when averaged across all invaded lakes. However, the full range of changes in the phytoplankton population ranged from a reduction of greater than 90 per cent to an increase in phytoplankton by 10 per cent. Impacts to higher-level organisms such as insects and fish were generally proportional to the impact on phytoplankton. This part of the food web, those biota (plants and animals) that live in the open lake, I refer to as part of the “pelagic” or “offshore” energy pathway. As noted, plants and animals within that pathway are generally negatively affected by zebra mussels. Another important energy pathway is the “benthic energy pathway,” which refers to plants and animals living on the lake bottom in shallow coastal areas. Biota in this pathway, such as algae attached to rocks, insects, crayfish and fish that live in the coastal areas, are expected to increase following the establishment of zebra mussels. In some cases, excessive blooms of coastal algae have occurred as a result of zebra mussels, fouling beaches, clogging water intakes, and creating strong odours and water quality problems when they start to decompose.

While most biota in coastal areas are expected to increase, an important exception is our native mussels. Because these mussels have hard shells, they are typically heavily colonized by zebra mussels, which smother and eventually kill them. A general rule of thumb is a 90 per cent reduction in native mussel populations within 10 years of zebra mussel establishment.

A common question is also: what will happen to our fisheries in affected lakes? Overall, the impact to fisheries will depend on: 1) the size of the zebra mussel population; 2) the effect of zebra mussels on key diet items in the offshore “pelagic zone”; and 3) the ability of target fish species to transition their diets to prey items in coastal areas.

Given these potential impacts on Lake Winnipeg and other lakes across Manitoba and the Western provinces, what should our provincial and federal leaders do? At this stage, the most important aspect of any zebra mussel management plan is to contain the problem to the locations currently invaded: Lake Winnipeg, Cedar Lake and the Red River. All boats, boat trailers and other equipment pulled from these locations must be decontaminated before being placed in another lake. Our public officials should ensure that information and infrastructure related to equipment decontamination is readily available for the public. Lake associations, parks and other organizations may want to evaluate the potential for their lake to be invaded (dissolved calcium levels above 12 mg/L offer conditions that could lead to zebra mussel establishment), and establish boat check stops and boater surveys at their boat launches. Most important is public action: the spread of zebra mussels can only be stopped by each boater ensuring their boat, trailer and other equipment are cleaned before moving them between lakes. Boaters should also expect more boater check stops, both in Manitoba and other Western provinces. Manitoba’s new aquatic species legislation, introduced in November 2015, includes many of these measures.

The impacts of zebra mussels on Lake Winnipeg will require new monitoring and research initiatives. Both provincial and federal action are required. We will need to expand provincial monitoring programs to include coastal areas, which are typically most affected by zebra mussels. Previously used indicators of water quality will need to be re-examined and new indicators developed. The federal government has the capacity to conduct and support research initiatives, infrastructure (e.g., permanent boat-washing stations at federal harbours) and coordinate actions between provincial jurisdictions. In terms of research, nutrient management plans and modelling efforts underwent a significant change in the Laurentian Great Lakes following the establishment of zebra mussels. Federal government scientists, particularly those within the Department of Fisheries and Oceans and Environment Canada, which dealt with these issues in the Laurentian Great Lakes, are well positioned to lead these efforts in Lake Winnipeg. They should involve academic researchers and their students where appropriate. Ultimately, the goal will be to predict and adapt our management of Lake Winnipeg (and other invaded lakes in the west) to the arrival of this new pest. Our federal and provincial governments must act in cooperation with the public, and the time to act is now.