These increases in jellyfish should be a warning sign that our oceans are stressed and unhealthy.

KOKONOGI, Japan – A blood-orange blob the size of a small refrigerator emerged from the dark waters, its venomous tentacles trapped in a fishing net. Within minutes, hundreds more were being hauled up, a pulsating mass crowding out the catch of mackerel and sea bass.

The fishermen leaned into the nets, grunting and grumbling as they tossed the translucent jellyfish back into the bay, giants weighing up to 200 kilograms (450 pounds), marine invaders that are putting the men's livelihoods at risk.

The venom of the Nomura, the world's largest jellyfish, a creature up to 2 meters (6 feet) in diameter, can ruin a whole day's catch by tainting or killing fish stung when ensnared with them in the maze of nets here in northwest Japan's Wakasa Bay.

"Some fishermen have just stopped fishing," said Taiichiro Hamano, 67. "When you pull in the nets and see jellyfish, you get depressed."

This year's jellyfish swarm is one of the worst he has seen, Hamano said. Once considered a rarity occurring every 40 years, they are now an almost annual occurrence along several thousand kilometers (miles) of Japanese coast, and far beyond Japan.

Scientists believe climate change — the warming of oceans — has allowed some of the almost 2,000 jellyfish species to expand their ranges, appear earlier in the year and increase overall numbers, much as warming has helped ticks, bark beetles and other pests to spread to new latitudes.

The gelatinous seaborne creatures are blamed for decimating fishing industries in the Bering and Black seas, forcing the shutdown of seaside power and desalination plants in Japan, the Middle East and Africa, and terrorizing beachgoers worldwide, the U.S. National Science Foundation says.

A 2008 foundation study cited research estimating that people are stung 500,000 times every year — sometimes multiple times — in Chesapeake Bay on the U.S. East Coast, and 20 to 40 die each year in the Philippines from jellyfish stings.

In 2007, a salmon farm in Northern Ireland lost its more than 100,000 fish to an attack by the mauve stinger, a jellyfish normally known for stinging bathers in warm Mediterranean waters. Scientists cite its migration to colder Irish seas as evidence of global warming

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