Grass carp is one of four species of carp known collectively as Asian carp.

(photo by Ryan Hagerty, courtesy US Fish and Wildlife Service/Flickr CC)

Overview

Invasive species are any species that have, primarily with human help, become established in a new ecosystem. While it’s impossible to say exactly how many invasive species are living in Canada, in 2002 researchers estimated that at least 1,442 invasive species — including fish, plants, insects and invertebrates — now live in the country’s farmlands, forests and waterways. The complex environmental impacts of so many invasive species is unknown and, maybe, unknowable. Typically, non-natives are feared for their ability to reproduce much faster than native species and outcompete natives for food, habitat and other resources. Economically, invasive species are estimated to cost Canadians billions of dollars each year in lost revenue from natural resources and impacts on ecosystem services.

Invasive species have the potential to affect every region in Canada. That said, the Great Lakes basin is one of the country’s most heavily affected ecosystems, with more than 180 known invasive species having arrived in the basin since the 19th century. Between 1970 and 2000 alone, a new invasive species was detected in the Great Lakes every eight months on average, leading some researchers to suggest that unless new regulations were put in place, countless new invasive species could become established in the Great Lakes by 2063.

Not all invasive species cause severe and noticeable effects on their new ecosystems. In addition, likely not all invasive species in Canada have even been identified yet, and others may simply be dormant. For example, there are dozens of invasive snail< and mollusc species in the Great Lakes watershed. But few beyond zebra and quagga mussels have been shown to have negative impacts on the ecosystem by filter-feeding huge quantities of phytoplankton, food that’s no longer available to numerous other species that depend on it to survive. Yet these dozens of snail and mollusc species may be causing problems that aren’t fully understood — researchers simply don’t know.

Scientists do know, however, that as greater numbers of invasive species arrive in a location, they can occasionally help each other prosper. In a process called invasion meltdown, some invasive species help other invasive species thrive by providing habitat or access to food that native species cannot equally share (see Case Study: Zebra and Quagga Mussels below).

How Do Invasive Species Spread?

Invasive species are often introduced to new habitats accidentally, though humans are almost always involved in some way. When ocean-going ships empty their ballast (a compartment at the base of the vessel, used to help it balance) in the Great Lakes, for example, that water, often taken on in distant parts of the world, can carry numerous species not native to the basin. Zebra mussels are just one of many species that have spread throughout North America after being introduced to the Great Lakes via ballast water from ocean-bound ships — others include round gobies, quagga mussels and faucet snails, in addition to numerous invasive plants.

Climate change is another key way invasive species spread throughout Canada. Deer ticks, known in the eastern United States for carrying Lyme disease, were once controlled by cold winters. Since the beginning of the 21st century, Lyme disease–carrying ticks have been slowly advancing north into numerous parts of Canada, including Ontario, Quebec, Nova Scotia, southern Manitoba, Saskatchewan and Alberta. In early 2016, the Canadian government was so worried about the ticks’ introduction to Canada and their ability to spread disease that Ottawa’s Public Health Agency investigated the issue.

Humans have introduced some species to new regions in Canada to serve an ecological function, or for recreational purposes. Chinook and coho salmon, for example, were intentionally stocked in the Great Lakes as far back as the mid-19th Century, but were increased in the 1960s both to control alewives (another invasive fish) and to create a sport fishery for salmon. Largemouth bass are another example of this. While largemouth bass are native to eastern North America, the fish is invasive in British Columbia’s Lower Mainland and Columbia River system, where they were introduced by anglers for sport fishing reasons. Once loose, largemouth bass have killed off many prey fish populations and spread disease to native species.

Why Are Invasive Species a Concern?

Invasive species are concerning for the following reasons: