Silver carp jumping in river
Invasive silver carp, which are native to China and Eastern Siberia, jumping in the Fox River, Wisconsin. Silver carp have spread to at least 88 countries around the world (photo courtesy Asian Carp Regional Coordinating Committee)
Wednesday, July 22 - 2020
Don Campbell

Nick Mandrak has just about seen it all over his 30 plus-year-career as an aquatic invasive species researcher.


From goldfish infesting local stormwater retention ponds, to pulling a bighead carp out a fountain just south of Queen’s Park, the stories range from cautionary to near comical, if the problem wasn’t so serious.   


Now he’s teaming up with an international group of researchers calling on governments around the world to adopt tougher policies on tackling invasive species before it’s too late.


“Both global warming and emerging global trade pathways are accelerating the spread of invasive species, and the problem is going to get worse unless something is done,” he said.


Mandrak, a professor in the Department of Biological Sciences at U of T Scarborough, along with more than 20 colleagues from across the globe, recently published a paper in Biological Reviews warning about the consequences of invasive species.


Since the 1970s, the researchers note that the number of invasive alien species (non-native species that invade an ecosystem and establish reproducing populations) has risen 70 per cent in 21 countries around the world that have data on invasive species. These species pose serious risks to the ecosystems they invade, including reducing the abundance and genetic diversity of native species and, as a result, increase the risk of native species’ extinction.

Nick Mandrak
Professor Nick Mandrak is a renowned expert on aquatic invasive species. He's joined an international group of scientists calling on governments around the world to adopt stronger policies on tackling invasive species (photo by Ken Jones)  

While most people tend to associate invasive species with obviously destructive pests like the emerald ash borer – which has destroyed millions of ash trees across Canada – or Asian carps, infamous for their jumping behaviour in the Mississippi River, many invasive species can subtly disrupt ecosystems by altering its ability to cycle nutrients. Mandrak points to the local example of round goby, an invasive fish species found in Lake Ontario that can outcompete native white sucker fish.


“Like salmon, native white suckers swim up stream every spring to spawn, leaving a lot of nutrients in the form of eggs and dead bodies behind when they do. This plays a big role in the entire nutrient cycling of Lake Ontario, which we will lose if they get outcompeted by round goby” said Mandrak, pointing to a preliminary finding by U of T Scarborough PhD Meagan Kindree.


Invasive species are also creating a situation where ecosystems around the world are becoming more similar to one another. Research in Mandrak’s lab by PhD student Sara Campbell has found that the Great Lakes are becoming more homogenized as a result of invasive species. What’s more, because of the human transfer of species to distant waterbodies around the world, the fish communities in places like the Black Sea and the Great Lakes are beginning resemble each other.


Mandrak said that if the environmental and economic impacts are not enough to convince people into action, there are also the potential consequences for human health.


He points to zebra mussel, an invasive species found throughout the Great Lakes linked to toxic algae blooms that can drastically affect water quality, or the Chinese mitten crab that carries a parasitic worm that can cause lung infections in humans, just to name a few.  


“We need to think of invasive species like viruses, except instead of invading our body they are invading our ecosystems,” he said.


“The scientific evidence is abundantly clear – these organisms are not native and they are having profoundly negative ecological, economic, and human health impacts. Our concern is that, despite all of this evidence, governments are still lagging behind in their response. What we’re saying, as scientists, is that it’s time to do something about it.”