Are jellyfish taking over the ocean?

They can sting, they can kill and they can cause real disagreement back on shore among those trying to read the future of the oceans and signals on climate change. Today we look at whether jellyfish really are about to take over and why that could be a really bad thing.

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They have no backbones and no brains but some fear jellyfish may be in the vanguard of a terrible invasion force

Lisa-ann Gershwin paints an alarming picture of how jellyfish populations are moving and growing in her book: Stung! On Jellyfish Blooms and the Future of the Oceans. Speaking on the CBC Radio's Quirks and Quarks, she argued the health of the oceans allows the jellies to make up for lost time.

Professor Tim Flannery is a scientist and the chief commissioner of the Australian Climate Commission. He has just written about Lisa-Ann Gershwin's book in the New York Review of Books. Tim Flannery believes climate change is leading to dangerous jellies being found in parts of the world they haven't seen before. He was in Sydney, Australia.

Not everyone is convinced the jellies are coming back to recover what they lost in the pre- Cambrian

Steve Haddock is a researcher at the Monterey Bay Aquarium Research Institute and he started the website jellywatch.org to accumulate more information about what is going on in the world's oceans.

He encourages people to send him reports ... big or small... of what they see. He hopes to get a better sense of the actual jellyfish population.

At the moment, he says there's just not enough evidence to say there are more jellyfish. But where the jellyfish have been studied, he says the numbers are cyclical and thinks the language used around jellyfish can be misleading.

As for the argument that climate change creates a welcome environment for jellyfish .... Steve Haddock says some of the jellies he studies would actually disintegrate ... not thrive... as the ocean warms.

"It is not impossible that certain species are rising due to climate change. But in the jellies that I study, which I think are more representative of what's in the ocean, even if the people don't encounter them, for them there's really no evidence that they're increasing. There's a fair amount of them and there have been for awhile. So I wouldn't say it's not happening but I haven't seen anything that is very convincing, that it is".Steve Haddock, Researcher at Monterey Bay Aquarium Research Institute

Scientists are working on developing evidence on growing jellyfish population

Lucas Brotz is a PHD student who works for the Sea Around Us Project at the University of British Columbia Fishery Centre. He's researching how jellyfish populations are changing.

Lucas Brotz's research shows some evidence that jellyfish populations are expanding but admits that jellyfish can be hard to really measure because they're there one day and gone the next. He was on the very west coast of Canada in Tofino, B.C.

The Vancouver Aquarium has an exhibit called the Jelly Invasion where people can appreciate the tentacled ones up close.

Have you ever been stung by a jellyfish?

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This segment was produced by The Current's Liz Hoath.

Last Word - Strange Weird Little Guys

We've heard different thoughts today about whether the jellyfish is really about to take over the world's oceans. We can only hope they don't. As we heard, the sting from a box jellyfish can kill before its victim has time to get out of the water. For today's Last Word, a nature lesson for tourists from the Australian band, Scared Weird Little Guys.