Some wobbly numbers

ABC report: Jellyfish numbers on the rise, expert says.
Seems Three people in Queensland have been stung by the irukandji jellyfish since New Year's Eve.
"Dr Gershwin says there have been huge, unexplained jellyfish blooms across the country. "It tends to be things like over fishing, climate change pollution too much fertiliser and too much sewage in the coastal waters," she said." (or perhaps periodic global fluctuations are to blame?-see below).
Meanwhile back in 1953: SIX PERSONS STUNG BY MARINE OBJECTS AT WEEK-END

"The cause has not been isolated but the sting has been named lrukandji, after an aboriginal tribe which originally inhabited the area between Trinity Inlet and the Mowbray River."

1954 also a bumper Jelly Fish year with "NINE Jelly Fish Victims at Yorkey's Knob". 

"Nine cases of jelly fish stings kept lifesaver first-aid groups busy at Yorkey's Knob yesterday and several other bathers were treated for minor cuts. One jelly fish sting victim,  a seven-year-old girl, was taken to hospital."

Sharks also a nuisance but it seems friendly flipper chased them away:
"The water was again cleared later in the- afternoon for a short period when a shark came within 30yards of the beach. Two porpoises chased it out to sea."

Back in 1934 Jelly Fish (not the irukandji) invaded Port Phillip Bay in: "such vast numbers as seriously to inconvenience bathers. Two years ago nets were used in beach bathing pools on Melbourne beaches to clear the water." Look out Melbourne for its seems "the invasion occurs", "Nearly ever year about the middle of February"! 

Who could forget the Trinity Bay Jelly Fish invasion of 1952? Trinity Beach Jelly-Fish Invasion

"For the last week the sea sklrting Trinity Beach has been thickly studded with jelly-fish of all-types. At least six different varieties of these horrible looking creatures have been counted, and.one specimen weighed 14 lb. The sight of them floating in the water or left stranded along the water line has made swimming most unpopular."

Fi

Or Lakes Entrance in April of the same year? Invasion of Jelly Fish At Lakes Entrance

"At Lakes Entrance Fishermen report an invasion of jelly fish to Lakes King and Victoria."

Blubberous jelly invasion at Newcastle in 1932:

"A jelly fish invasion on a scale unprecedented in the history of Newcastle beach made surfing practically impossible after mid-day on Friday. Lunchtime surfers walked down to the water's edge, watched the glistening mass of blubber, which littered the beach, and went back to the pavilion to have a shower."

The 1955 Port Phillip Bay  jelly "catastrophe": Catastrophe in bay feared: 

"Unless nature steps In with a strong northerly blow to send the dinoflagellates (fish-killing "jelly") out of the bay, fishing will take at least five years to recover."

"Millions of young, inch-long fish were also being killed, with sand worms, crags, and many types, of shell fish." 

Cronulla, March 1939:  Many Rescues in Surf
"Lifesavers effected many rescues in big seas on metropolitan beaches yesterday. Their task was made more hazardous by the invasion of armies of"blue-bottles" and jelly-fish."

Also in 1939 Britain invaded, not by Germans by Jelly Fish!: BRITAIN INVADED-BY JELLYFISH.

"Great Britain is being Invaded by a plague of millions of jellyfish, causing fishermen to stay in port, swimmers to swim inshore, and giving' marine scientists a headache."

The Jelly fish so common in 1936 it even rained jelly fish..."During a shower of rain at Frankston, near Melbourne, clouds, of little brownish creatures fell from the sky and covered the streets.The little creatures were jellyfish, about half an inch long and a quarter of an inch wide."

In 1937 they even caused a blackout! JELLYFISH CAUSE BLACKOUT IN BRISBANE. You'd have thought someone might have done something about it seeing it happened in 1931! Jellyfish Stop Generator. Some lessons never learnt (at which point some recent flooding comes to mind).

And in 1907 these FISHERMEN'S ENEMIES arrived in Portland Bill (UK) in "Plague" proportions. Perhaps descendents of the great Scrabster bay plague of 1886?

In 2012 ABC report three people being stung. In 1952 it was: "a daily average of 10 sufferers."

In regard to the numbers it seems other experts are saying otherwise. Not that ABC thought to ask them!
Jellyfish population booming worldwide; or is it?
Study: No Evidence Of Increasing Jellyfish Population Over Last Two Centuries

In regard to the cause, seems some experts agree it is due to something other than "over fishing, climate change pollution too much fertiliser and too much sewage" : Jellyfish experts show increased blooms are a consequence of periodic global fluctuations.

The key finding of the study shows global jellyfish populations undergo concurrent fluctuations with successive decadal periods of rise and fall, including a rising phase in the 1990s and early 2000s that has contributed to the current perception of a global increase in jellyfish abundance. The previous period of high jellyfish numbers during the 1970s went unnoticed due to limited research on jellyfish at the time, less awareness of global-scale problems and a lower capacity for information sharing (e.g. no Internet).