Watch CBC Wild Docs online: Episode 7 Jellyfish Invasion

The curse of beach holidays, explores why the jellyfish population is exploding. They have become the curse of beach holidays, permeating every ocean on the globe, thriving in the arctic and the tropics. In an ever-changing world where other species struggle to endure, jellyfish populations are on the rise. To the untrained eye, they're gelatinous blobs, drifting aimlessly on the ocean's currents. But jellyfish are among the most-feared and least-understood creatures on earth. And their populations are exploding across the world. They lack sharp claws, piercing teeth or even a brain - but they are armed with an amazing arsenal of weapons. For hundreds of millions of years, jellyfish have been evolving, developing into the ultimate survivor. The wet season, Northern Australia. Here locals and tourists alike have long been wary of the lethal sting of the largest box jellyfish, the sea wasp. These creatures are not aggressive and usually avoid human beings, but accidental collisions are inevitable. And on a continent loaded with deadly predators, it's the box jellyfish that's the most venomous. Since 1900, the creature has killed some 80 people in the waters off Australia. One brush with its tentacles delivers horrific pain and can be fatal. But why does this jelly defend itself like this? Australian jellyfish expert Jamie Seymour introduces us to the Irukandji jellyfish. No bigger than a penny and translucent by design, the Irukandji is nearly impossible to detect in the ocean, but those who've encountered the lethal jelly certainly don't forget. Its venom packs a staggering punch, and its toxins permeate the body with startling efficiency. Swarms of Irukandji are now being reported worldwide. We discover that while a paralyzing defense is the key for jellyfish survival, there may be a new factor enhancing its ability to survive: human-generated changes to the waters they live in. To investigate this phenomenon we go to Japan, where the population of jellyfish, hundreds of pounds heavier than the Irukandji is growing so fast, it's transforming marine environments. Known as Nomuras, these giant jellyfish are now blooming in unimaginable numbers. Since 2002, they have poured into the Sea of Japan by the billions, wreaking havoc on the fishing industry. As similar blooms crop up around the world, scientists are forced to wonder: is man somehow responsible?

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