One of Canada's worst invasive species may have arrived naturally

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Most invasive species are introduced into the areas where they become damaging. That's part of why they tend to be so successful in taking over new environments and causing billions of dollars in damage.

But what if species that we thought were introduced by humans arrived naturally? In our recent research paper, we made a startling discovery about one of North America's most ecologically and economically damaging invaders. The spiny water flea, also known by its scientific names Bythotrephes longimanus and Bythotrephes cederströmii, may have been in North America for centuries longer than believed.

Our finding has implications for how governments and conservation organizations approach invasive species management. Millions of dollars are spent to control the spread of invasive species, but for native species that benefit from environmental change, this strategy may misplace limited funds. The widely accepted history of the spiny water flea is that it was introduced unintentionally from Europe into Lake Ontario by trans-Atlantic cargo ships in the early 1980s.

In our study, we found reports of the spiny water flea in more than 300 lakes and rivers across Canada and the United States over the past four decades. This number is likely a massive underestimate because most lakes are not monitored. Identification of the spiny water flea relies on physically detecting it in water with nets or inside fish stomachs.

Several million water fleas may need to be present in a lake before a single individual is caught in a net. This means only the densest populations may be detected. In 2019, our co-authors made an unexpected finding.

Sifting through mud at the bottom of Three Mile Lake in Muskoka, Ont., they found the jaws of the spiny water flea. Over time, particles and dead organisms settle to the bottom of lakes. New material accumulates on top of older layers, creating a natural archive of the lake's history.