Climate change can dramatically increase invasive mussel numbers

Climate change will bring warmer water temperatures and more intense storms to one of Ontario’s most popular fishing spots. These factors will change the water dynamics of Lake Simcoe resulting in dramatic increases in the number of invasive mussels, according to a new study.

Using a new modelling tool to predict the impact of two kinds of invasive mussels - zebra and quagga mussels - scientists have shown that a 60 per cent increase in the intensity of three summer storms is enough to expand mussel colonies.

“Lake Simcoe has undergone profound changes in the past thirty years,” says Ralph Smith, a Biology professor in the Faculty of Science and co-author on the paper. “Not only has it been hit by dreissenid mussels, climate change is now having an effect as well.”

Mussels are stationary and live along the upper edges of Lake Simcoe. Their food supplies are limited to the upper lake levels but weather events, such as storms, act like a cocktail shaker and mix up the water layers – bringing fresh supplies of phytoplankton for the mussels to feed on which encourages them to multiply.

Warming the lake’s surface and creating a stable, stratified water layer acts in the opposite way,  but the warmer temperatures will be more comfortable for the mussels and will help them to grow faster.

The study from the University of Waterloo, Queen’s University, Environment Canada and the Ontario Ministry of Environment, is published in the current issue of Aquatic Sciences.

As climate predictions improve, managers can use this tool to predict a variety of scenarios, including how the mussels influence the viability of certain fish species, such as lake trout, small mouth bass and yellow perch.

Knowing which sports fish will thrive is an important management consideration as Lake Simcoe is one of Ontario’s top recreational fishing destinations.

The tool also predicts invasive mussels will have a considerable impact on phytoplankton - an important food source for fish - in the lake. The quagga mussel filters more than a litre of water a day which clarifies the water allowing sunlight to penetrate the lake more deeply. Smith, along with Waterloo biologists Bob Heckey and Stephanie Gillford (both now retired), and William Taylor believe the additional sunlight combined with nutrient rich waste from the mussels promotes algae growth.

Zebra and quagga mussels have changed the ecology of some of the largest lakes in the world and have cost governments more than $7 billion in damage since 1988 according to the Ontario Ministry of Natural Resources.

Postdoctoral fellow Astrid Schwalb was first author on the paper.  Environment Canada’s Lake Simcoe Cleanup Fund funded the project.