A mystery box jellyfish spotted in Sydney waters may belong to a new species entirely, an expert working to identify the marine animal has said.
The sightings of the jellyfish outside of tropical waters have prompted warnings about correct first aid for marine stings.
Two encounters with the jellyfish were caught on camera by Scott Belcher, a Sydney resident, who first spotted it a fortnight ago during a group ocean swim near Cronulla’s Shark Island.
“We swam a little further down south to Shelly beach and ran into what I thought was a rather large jimble,” he said, “but filming it [we] realised that it’s a lot meaner.”
The jimble, Carybdea rastoni, is a species of box jellyfish with only four tentacles which can deliver a painful but not dangerous sting.
The new species had several tentacles around 30cm long and more closely resembled the deadly Australian box jelly, Chironex fleckeri, also known as the sea wasp.
“The head of the jellyfish was about as big as your palm,” Belcher said.
He filmed another encounter six days later of what is believed to be a second jellyfish of the same species.
“It’s just unbelievable that I was in the right spot at the right time with my camera working.”
Dr Lisa-ann Gershwin, a jellyfish expert in Hobart, said it was possible the Cronulla specimens belonged to a new species.
“It is not Chironex fleckeri, the one we lovingly refer to as the box jellyfish,” Gershwin said.
“But it is a box-shaped jellyfish which is closely related to Chironex. My very first reaction was … that does not belong in Sydney.”
She is working with the Australian Museum to characterise the species, which she said resembled an unidentified specimen held in the museum’s collection since 1984.
Another possibility was that the Cronulla sightings were larger specimens of Chiropsella saxoni, a 3cm pygmy box jellyfish, which was discovered in Queensland and which Gershwin identified as a new species in 2015.
Gershwin said it was difficult to determine whether the new jellyfish was toxic because it had a mix of features of both non-dangerous jellyfish and also the Australian box jelly – the world’s most venomous marine animal.
“In my experience studying the box-shaped jellies of the world … all of the ones with thick tentacles are dangerous, and all of the ones that are not dangerous tend to have thin tentacles,” she said. “The problem is the Cronulla ones have thick tentacles.”
But other structural features of the new jellyfish resemble those of non-dangerous species, including the presence of round gastric saccules – “little gelatinous knobs on the inside of the body”.
Gershwin said there had been scattered sightings of deadly Australian box jellies in New South Wales over the past few decades, but no footage or recovered specimens.
“Any jellyfish that someone gets stung by outside the tropics is automatically assumed to be a bluebottle,” she said.
“Most people don’t realise that there is an Irukandji [the species Morbakka fenneri, which Gershwin characterised in 2008] that is native to NSW, that has been stinging people … since 1905.”
For jellyfish stings outside tropical areas, the Australian Resuscitation Council recommends rinsing the sting well with seawater and then using hot water or ice for the pain. It is “standard and appropriate treatment”, Gershwin said, emphasising the importance of washing the sting with seawater first.
She advised against immediately using hot water on suspected box jellyfish stings. “Freshwater forces stinging cells to discharge, so it increases the venom load, and heat dilates the capillaries, basically opening the floodgates for the venom to circulate around.”
A handy rule of thumb for jellyfish stings, Gershwin said, was that bluebottles were usually found in armadas.
“If you get a sting, you come out of the water and there are no bluebottles up and down the beach, then the right assumption would not be that it’s a bluebottle.”
