Massive jellyfish swarms are latest symptom of overheating planet

‘You can definitely say that global warming contributes to these massive swarms’

Huge numbers of jellyfish have turned up in swarms off Israel’s Mediterranean coast.

There are so many of the gelatinous creatures that they threaten to clog up the desalination plants used to supplement the country’s water supply and send swimmers back onto dry land.

One reason there might be so many jellies? The climate crisis.

"The water gets hotter and hotter and we can see more and more jellyfish," Guy Lavian from the Israel Nature and Parks Authority told Reuters. "They cause real damage here. You can definitely say that global warming contributes to these massive swarms."

This month’s Israeli jellyfish bloom occurred off the coast of Haifa, a city in the country’s north. But at least one study has found that many jellyfish populations around the world have been increasing since the 1950s.

That study noted that jellyfish populations have increased in places as far flung as the northeast United States, Japan, Hawaii and even Antarctica.

Warmer waters tend to lead to more jellyfish, notes the Scripps Institution of Oceanography at the University of California, San Diego, which could mean some places will see more jellyfish as the oceans heat up.

Some 90 per cent of the excess heat caused largely by burning fossil fuels has ended up in the ocean, according to the Woods Hole Oceanographic Institute.

All that heat is taking a toll. Since 1901, the uppermost layer of the ocean, where most marine life is, has warmed by 1.5 degrees Celsius, Woods Hole adds.

The effect of this warming on jellyfish populations may not be uniform however, Scripps notes. Jellyfish numbers could decline in some places if their food sources start to deteriorate.

Jellyfish could be impacted by consequences of the climate crisis beyond global heating. For one, the climate crisis is driving down oxygen levels in the ocean — and some jellyfish are tolerant of lower-oxygen environments, which could make them more dominant, Scripps notes.

But the climate crisis is also making the ocean more acidic, and scientists don’t yet know how a more acidic ocean could affect our stinging, tentacled companions, they add.

No matter what, jellyfish are a link to marine ecosystems that have been long extinct. Scientists have found jellyfish fossils more than 500 million years old — meaning they’ve watched the dinosaurs both come and go in their long lifespan.

Reuters contributed to this report