It sounds like the opening scene in a 1950s horror film: Stinging jellyfish populations are growing and threatening fishermen, surfers and ocean-going tourists.
But it's true, according to a group of University of British Columbia researchers who report the growth in jellyfish numbers in almost every ocean, especially in areas with heavy concentrations of human activity, according to the National Post.
The results of the research were published this month in the journal Hydrobiologia.
"There has been anecdotal evidence that jellyfish were on the rise in recent decades, but there hasn't been a global study that gathered together all the existing data until now," lead author Lucas Brotz, a PhD student with the Sea Around Us Project at UBC, said in Science Daily.
"Our study confirms these observations scientifically after analysis of available information from 1950 to the present for more than 138 different jellyfish populations around the world."
According to Science Daily, they found jellyfish populations in 62 per cent of the regions analyzed. Coastal Europe and Asia and the Black Sea in eastern Europe have been hit hardest by so-called jellyfish blooms.
Antarctica has also been inundated, according to the study, but most of North America's coast has been spared so far.
Brotz told the Post jellyfish trapped in fishermen's nets have been known to capsize fishing boats, and can clog drainpipes and seawater intake valves at power plants.
"By combining published scientific data with other unpublished data and observations, we could make this study truly global -- and offer the best available scientific estimate of a phenomenon that has been widely discussed," co-author Daniel Pauly, principal investigator of the Sea Around Us Project, said in Science Daily.
"We can also see that the places where we see rising numbers of jellyfish are often areas heavily impacted by humans, through pollution, overfishing, and warming waters."
Pollution and overfishing are among the biggest factors responsible for the recent blooms, Brotz said. Fewer fish in the oceans mean more food available for jellyfish and also a decreased threat from predator fish, such as salmon.
Jellyfish are found in almost every coastal zone, the Post noted, and some even live in fresh water. Some species can grow to two metres in diameter and weigh more than 200 kilograms. The lion's mane jellyfish, found in Canada's Arctic and north Pacific oceans, has tentacles that can reach more than 30 metres.
Brotz pointed out jellyfish stings kill about 40 people a year, compared with eight killed by sharks.
There is a small upside to this jellyfish population boom; some Asian cuisines value them as a "slippery, healthy treat," the Post said. Brotz compares cooked jellyfish to "watery calamari, without much flavour."
Brotz added that Russians harvest jellyfish and grind them up to be used to strengthen concrete. They're also used in pet food.