A BLOOM of jellyfish has invaded Coolum Beach, leaving surfers and swimmers in hot water.
Thousands of Catostylus mosaicus, aka "blue blubbers", are speckling the water like blue and white polka dots.
Coolum lifeguard Michael Daly said about 20 to 30 people had been stung in the past week.
"Thankfully most of the blubbers stayed out behind the breakers in the deeper water," he said.
"If more had ventured into the bathing area then these figures would have been much higher."
Mr Daly said the sting was mild but still caused red swollen welts.
"The best way to treat the affected area is to wash it with warm to hot water," he said.
A photo of the bloom posted in Coolum Boardriders Facebook group has become a talking point among members.
"In my 30-something years here I have never seen this at Coolum, maybe Redcliffe," Jan Kelley said.
Dr Merrick Ekins, the collection manager of Sessile Marine Invertebrates at Queensland Museum, said the blue blubbers bloomed in Queensland annually.
"We are not exactly sure why but it relates to the warm weather," he said.
"Blooms were spotted around the Redcliffe area over summer so it appears they are moving north.
"They don't often stick around for long."
Dr Ekins said there was still a lot to learn about jelly
fish and their behaviour.
"It is quite exciting, there are new species discovered all the time," Dr Ekins
The jellyfish bloom is thinning out at Coolum but they are at other beaches as well and swimmers should still take care.
Catostylus mosaicus, aka the blue blubber jellyfish, is a species from coastal regions in the Indo-Pacific.
Its name is slightly misleading because in southern Queensland and Victoria it is blue, whereas in the Sydney region it is white or brown due to the presence of plant cells in the substance of the body.
It eats mainly plankton, small fish, some crustaceans, and small particles in the ocean water.
The blue blubber has a dome-shaped bell that can grow to 35cm across.
The sting can be sometimes painful but generally poses no serious risk to humans.
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