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Steamy summers bring jellyfish to surface of Manitoba lake

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It's a strange sight for Manitoba cottagers that may become more common with hotter summers, scientists said. For the second time in two years, Star Lake residents have spotted hundreds -- if not thousands -- of little, translucent jellyfish.

"They're neat to watch, but you wonder how will this species grow," said longtime Star Lake cottager Larry Santa, who saw the jellyfish on Monday when out boating. "Will it grow out of control?"

The dime- to nickel-sized freshwater jellyfish, known as Craspedacusta sowerbyi, were spotted in Star Lake in August 2010, for what cottagers said was the first time. The jellyfish have returned this year, said Santa, who took a few in a jar back to Winnipeg.

However, scientists said the harmless jellyfish have been in Manitoba lakes for decades. The first reported sightings brought to retired biologist Lane Graham's attention were during the 1970s.

"They've always been there. People just haven't seen them," said Graham, a former University of Manitoba professor. "They're only there if the water temperature is warm enough, long enough."

Graham said the jellyfish can spend decades in the polyp stage of their life cycle at the bottom of the lake creating more polyps. They only float to the surface when they reach the medusa stage -- what a typical jellyfish looks like -- when the water is warm.

But with hotter summers in Manitoba, we may be seeing more jellyfish, he added.

"They would occasionally occur and now they're happening more, recently," Graham said.

Santa said in his 35 years at Star Lake he has never seen jellyfish until the bloom two years ago. There are not only more this year, but that they also have a more greenish colour, which Graham attributes to the jellyfish eating more algae-eating plankton.

Although Craspedacusta sowerbyi is an invasive species from China, it has been in North America since the 1800s, making them more integrated in our ecosystems, said Graham.

"They're pretty much harmless," he said. "They feed on plankton, water fleas," adding it's OK to swim when jellyfish are around.

Manitoba Conservation and Water Stewardship said the jellyfish are a concern because the effect they have on Manitoba ecosystems is unknown.

"Aquatic invasive species can significantly alter the ecology of lakes, rivers, and streams, out-compete native species for food and other resources, affect recreational activities and can cost millions of dollars to control," said a provincial spokeswoman.

jennifer.ford@freepress.mb.ca

Republished from the Winnipeg Free Press print edition September 6, 2012 A2

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