Incredible Species Newsletter - Aquatic Invasives

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Under Water Invaders?

When you think of alien invaders you tend to look up into space. But some alien invaders are lurking in the water.

What Exactly Are Invasive Alien Species?

They're species that have been moved outside their range and are very successful at spreading in their new environment. Aquatic invasive aliens are the bullies of the water world. They take more than their fair share of food and can squeeze out native species. They upset the balance in their new habitat.

Learn how ballast water can carry invaders

Are all alien species a problem? No. We have lots of alien species in Canada that do not cause any problems. But you can never tell what will happen when you introduce a species to a new environment. It could quickly become a monster!

Flying Fish

Imagine being hit in the head by a 100 pound fish! Some US boaters have been injured by massive silver carp that leap up to 10 feet out of the water. (The vibration of motor boats causes them to jump.)

The silver carp is just one of a number of types of Asian carp that have become invasive aliens in North America. The Asian carp was originally brought into the Southern US to help reduce algae on catfish farms.

Flying Silver Carp Photo: Jason Jenkins

Floods washed the carp into the Mississippi River where it has become a major problem. An underwater electric barrier was constructed to keep the carp from getting into Lake Michigan. But the Asian carp seems determined to expand its territory and scientists now believe that the carp has made it past the barrier.

What has one large black eye, a long spiny tail with barbs on it and four pairs of legs?

It sounds like a monster but it's actually a tiny crustacean called the spiny water flea.

Though it's only about 1 cm (3/8 in) long, it's causing big trouble.

Photo: Bruce Doran
St. Lawrence River Institute

It's believed the spiny water flea came to North America on ships from Great Britain and Northern Europe. One reason this tiny creature is a problem is because it eats massive quantities of zooplankton. Small native fish, such as perch, need zooplankton to survive. The spiny water flea has spread throughout the Great Lakes and may cause native fish populations to decline.

Unfortunately, the spiny water flea has few predators in North America. Small and young fish choke on its long, sharp tail when they try to eat it. The spiny water flea can reproduce very quickly and its eggs can even survive Canadian winters so the population is increasing rapidly.

The Vampire of the Great Lakes

Another aquatic invasive alien doing damage in the Great Lakes is the sea lamprey. This is a jawless fish that sucks the blood of other fish.

This vampire originated in the Atlantic Ocean and snuck into the Great Lakes through canals. Its victims are often killed in the blood sucking process.


The Rusty Crayfish – Another Bully!

This aggressive little crayfish looks like a fighter and acts like it too. Originally from the Ohio River basin, the rusty crayfish was brought into Ontario as fishing bait around 1960. It has now spread to many inland lakes.

Rusty Crayfish Photo: Dr. Philip Myers, U. Michigan

The rusty eats twice as much as native crayfish. It likes to eat fish eggs and aquatic life that other crayfish and young fish like. By clawing up aquatic plants it destroys habitat for invertebrates as well as sheltered areas and nesting sites for fish. It's just a bit too big to be eaten by the fish that usually eat our native crayfish. All in all, the rusty crayfish is a bully that forces out all its competition. Just about the only good thing about it is that it eats zebra mussels, another harmful invasive species. If you like to go fishing, you should learn how to identify rusty crayfish and other aquatic invasives and never use them as bait.

Rusty Crayfish

  • Up to 10 cm (4 in) long, not counting the claws
  • rust coloured patches on each side of the shell (carapace)
  • claws can be grayish green to reddish brown
  • claws have an oval gap when closed
  • prefers river or lake beds where it likes to hide under rocks and logs

What species lays 30,000 to a million eggs a year? The zebra mussel – another aquatic invasive alien in Canada.

Zebra Mussels Photo: Public Library of Science

Rock Snot – Yuk!

A species of algae known as didymo began spreading wildly on Vancouver Island in the 1990s. This once harmless plant has started acting like an invasive species - spreading across the continent. Nicknamed "rock snot" for obvious reasons, it's also been called "toilet paper algae". You can understand why this disgusting looking plant might scare swimmers away.

Photo: Tim Daley, PA DEP

Rock snot can clog river bottoms with carpets of brownish goo. These slimy mats attract numerous flies which bury themselves into the algae's flesh. Unfortunately, these are the same flies that could provide food for fish. Rock snot not only steals food from the fish but also overtakes their habitat. It smothers any other vegetation. Just one cell of this plant can start a whole new colony. To be safe, you should disinfect your fishing equipment if you've been anywhere near it. Fly fishers should clean their boots well.

Researchers are still trying to figure out if didymo is native to Canada and why it suddenly started acting like an invasive species.

How Do You Know If It's Rock Snot?

  • Colour: Beige, brown or white, but not green
  • Touch: It looks slimy but it's not. It feels spongy or scratchy, like cotton wool.
  • Smell: It has no distinctive odour.
  • Strength: It sticks firmly to rocks and doesn't fall apart when you rub it.

For more information about alien invasive species please visit the Environment Canada website

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