It is claimed that climate change will cause deadly Irukandji and Box Jellyfish to invade Sydney Harbour – data shows otherwise

Story submitted by Eric Worrall

The Daily Telegraph warns that deadly Box Jellyfish and Irukandji jellyfish will invade the popular beaches of Sydney Harbour, if we don’t mend our wicked climate ways.

According to the article, which reads like a “B” grade horror movie, Macquarie University’s Professor Rob Harcourt claims that warmer currents are enabling more deadly tropical species to survive further south. 

“Every year scientists from Sydney Institute of Marine Science are taking a tally of new visitors to Sydney waters,’’ he said. “Like Nemo and his friends, the turtle ‘dudes’, lots of tropical animals travel down the east coast each year being swept along in the East Australian Current (EAC).”

Box jellyfish have been blamed for 64 deaths (ever) while the tiny irukandji jellyfish killed two people in north Queensland in 2002.
As someone who regularly swims in the Coral Sea, one of the places where these nasties live, I would like to point out that the risk of being killed by a Box Jellyfish or Irukandji is somewhat less than the risk of being killed in a car accident, or the risk of being struck by lightning.

But a story about killer jellyfish probably sells more newspapers, than a story about yet another irresponsible drunk.

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UPDATE: (by Anthony)

A check of the range for the Box Jellyfish shows it nowhere close to Sydney:

Source of base map: http://oceana.org/en/explore/marine-wildlife/box-jellyfish

The distance to the most southern point in the range from about North of Townsville (near the Cape Tribulation warning sign at the head of this post) to Sydney is over 1000 miles. It seems the claim of migration is more than a bit of a stretch.

Here is a plot of the average water temperature of Bondi Beach in Sydney:

Source: http://www.surf-forecast.com/breaks/Bondi-Beach/seatemp

Note the extreme barely breaks 25°C (77F)

And the science says otherwise. From Stingeradvisor.com

 

Box jelly and Irukandji jellyfishes are generally reported at water temperatures above 26°C.

In laboratory conditions, 1-2° warming results in stressed animals that do not recover; animals generally deteriorate rapidly and expire if not maintained in cool water.

Cooler water retains more dissolved oxygen, allowing animals to absorb it with less energy expenditure; cubozoans, with a higher metabolism than most other jellyfishes, and thus higher oxygen demand, probably have a narrow range of tolerance and low adaptational potential. Although the jellyfish are able to swim well, and thus navigate in and out of variable local conditions, the populations are nonetheless tied to regions where their polyps can survive; cubozoan species and populations typically have extremely narrow distributions, suggesting that they are unlikely to adapt easily to alternative habitats if conditions were to become intolerable.

 

Summary of published conclusions: Most authors have concluded that the jellyfish situation is likely to worsen in coming years, as human activities continue to impact on marine environments and other species are affected, opening up niches for jellyfish.

 

BOTTOM LINE: It seems likely that non-thermal perturbations are likely to result in increased jellyfish numbers, whereas thermal perturbations are likely to have detrimental effects on box jellyfish and Irukandji populations