Here’s your weekly Science Matters column by David Suzuki with Faisal Moola.
We must fight the alien invasion – for the sake of biodiversity
Last year, customs officers at the Vancouver airport got a surprise when they checked the luggage of a woman returning from China. They found 70 live Shanghai hairy crabs!
Meanwhile, people in England seem reluctant to flush unwanted goldfish down the toilet. So they give them a new home in the Thames River.
Back in Vancouver, if you walk through Stanley Park this summer, you’ll come across a pretty spot called Beaver Lake. It’s covered in water lilies and is home to red slider turtles and bullfrogs.
What’s the common thread? It’s all about invasive alien species. These are plants and animals that end up in an environment where they weren’t previously found – usually with help from humans – typically causing harm to the native species and ecosystems they interact with.
Most invasive species share ecological characteristics that give them an edge over native flora and fauna in competing for resources such as nutrients, light, physical space, water, and food. These characteristics include the ability to reproduce quickly and disperse throughout the environment, as well as tolerance to a range of habitat conditions.
Thus, although the hairy crabs may have been destined for the cooking pot, as the woman claimed, customs officers couldn’t take that chance. Environment Canada notes that the crab is one of the 100 most invasive species in the world. They compete with native species for food, they tunnel into riverbanks and dikes, causing erosion, and they carry parasites that can make people sick.
The Thames goldfish also compete with native species for food and transmit diseases to competing species.
In Beaver Lake, the lilies are speeding the demise of the lake itself, rotting and decaying in the fall and turning the lake into a bog.
The United Nations has declared May 22 as the International Day for Biological Diversity, and this year’s theme is invasive alien species. The UN Convention on Biological Diversity notes that these plants and animals constitute "one of the greatest threats to biodiversity, and to the ecological and economic well-being of society and the planet."
Introduction of a species from one environment to another is nothing new. Early European explorers and settlers brought with them to North America livestock and grains that weren’t previously found here, as well as stowaway Norway rats and numerous diseases.
But globalization and human movement have increased the spread of invasive species worldwide. As with plants and animals introduced by European settlers and explorers, today’s invasive plants and animals are sometimes deliberately introduced – often for food or decorative purposes – and are sometimes accidentally introduced, as with zebra mussels and invasive plants spread when ships empty their ballast in Canadian waters.
As well as competing for resources, many alien species kill and feed on native plants and animals. They can also alter habitats, making them uninhabitable to plants and animals that previously lived there. And they can breed with native species and weaken the gene pool. The economic impacts can also be severe, as when, for example, valuable food crops or species are wiped out.
Because they enter in so many ways, these invaders can’t be stopped through laws alone – although laws can help when it comes to things such as regulations governing where and when ships’ ballast water can be dumped.
Education is one of the best ways to slow the spread. Often people are unaware of the consequences of introducing new species to an ecosystem.
Cooperation at local and international levels is also essential. Canada joined the United Nations Convention on Biological Diversity in 1992 and developed the Canadian Biodiversity Strategy in 1995, with the goal of monitoring and controlling importation of alien species.
Once an introduced species has established itself, it is extremely difficult to eradicate. Targeted control is commonly used where species have already been introduced. This can range from removing the alien species to using pesticides or herbicides to introducing native predator species.
We should all become aware of alien invasive species and the ways they are spread. Many communities have volunteer programs to get rid of these species. In Vancouver’s Stanley Park, people volunteer to pull out the invasive English ivy that has grown throughout the park, choking many of the park’s native plants.
We can’t entirely stop the spread of these alien invaders, but we can all pitch in to make sure we keep our ecosystems as healthy and natural as possible.
Science Matters has been running weekly since 1999. To read past columns, please visit www.davidsuzuki.org/science_matters/.
Take David Suzuki’s Nature Challenge and learn more at www.davidsuzuki.org.