Jellyfish populations seem to be increasing in many of the world's oceans, especially in areas where there is pollution, overfishing and other impacts of human activity, a B.C. study has found.

Since 1950, numbers of the stinging, tentacled sea creatures appear to have increased in 62 per cent of 45 coastal ecosystems analyzed, reported a study led by University of British Columbia Ph.D. student Lucas Brotz and published in the April issue of the journal Hydrobiologia. They have decreased in seven per cent of these systems and remained stable in the rest. 

The areas where they are increasing tend to be ones affected by human development, suggesting that jellyfish could be indicators that humans are degrading the ecosystem, Brotz said.

Scientists aren't sure why, but they think it's because such degradation has a more negative impact on other species.


Jellyfish could be indicators that humans are degrading the ecosystem, said Lucas Brotz, shown diving with a lion's mane jellyfish in Indian Arm, B.C. (Conor McCracken)

"It does appear that jellyfish will suffer less that these other organisms," Brotz told CBC's As It Happens. "They're potentially released from competition and predation, and in that sense they can thrive and do better than the other organisms that are out there."

People in coastal communities have complained for years about increasing numbers of jellyfish, which can make themselves a nuisance by stinging swimmers, clogging the intake pipes of water and power plants, and interfering with fishing.

Brotz wanted to find out if the complaints were the result of actual increases in jellyfish populations rather than increased human activity on the water, and how pervasive and widespread the changes in jellyfish populations might be.

In order to do that, he combined many sources of data on jellyfish abundance on different species in different parts of the world from between 1950 and the present day.

It included both published and unpublished data, including anecdotal data, such as reports about an increasing proportion of jellyfish netted accidentally during fishing.