Escaping the summertime blueys

It turns out we really don't know much about these mysterious blue creatures. But what little is known is downright peculiar, to say the least.

Firstly, contrary to what many may think, the bluebottle isn't a jellyfish. It's actually more closely related to coral, although bluebottles and jellyfish both fall under the same phylum, Cnidaria.

Three distinct species have been identified by a team at Yale university using samples from UNSW scientists, with at least two of them in Australia.

Physalia physalis (pictured above) is the Atlantic Ocean species, once thought to be the same species as the ones we see in Australia that are common to the Pacific Ocean.

Also known as the Portuguese man o' war, the Atlantic species is notably larger than the Pacific varieties, measuring up to 30cm, with up to seven tentacles that may extend up to 10s of metres in length. Proving that Australia doesn't have the monopoly on deadly, poisonous animals, physalis delivers a very painful sting which in some cases has been fatal.

Physalia utriculus (above) is one of the two known species found in the Pacific Ocean and frequently encountered in Australia.

It's much smaller than the Atlantic species, with a float in adults averaging about 5 to 10cm in length. Unlike physalis, utriculus only has one stinging tentacle that may extend a few metres. The sting, while painful and causing discomfort and rash, is not considered fatal.

Recent research suggests the utriculus bluebottle frequents the east coast of Australia in large numbers during the summer months January and February – which is the second peak wave of the warmer months. It's distinguishable from the other Pacific bluebottle species, Physalia megalista (pictured below) which has a relatively longer nose.

Megalista is common on the east coast of Australia in late spring and makes up the first wave of bluebottle beachings ahead of the approaching summer.

Strange, but true

Like coral, bluebottles are not one animal but a colony of four genetically identical individuals – called zooids – that allow the bluebottle to function as a single organism.

If they have the same genes, how could they be separate animals? The answer is that theoretcially they can detach and live apart - but it woundn't be for very long as they each need the other three zooids to survive.

Sting in the tail

Unlike bees, wasps and other animals that sting out of self-defence, a bluebottle's sting functions as a biological fishing line, with fish and larvae comprising 70-90% of their diet.

The tentacle sting is packed with nematocyst cells – barbed, coiled threads that shoot venom into unfortunate fish and the occasional human.

Once a tentacle comes into contact with its prey, the paralysed prey is carried up towards the gastrozooids near the base of the float. The gastrozooids respond immediately and begin writhing and opening their mouths. Many gastrozooids attach themselves to the prey – upwards of 50 gastrozooids have been observed to completely cover a 10cm fish. The gastrozooids release proteolytic enzymes to digest the fish.

Biological oddities

UNSW's Dr Amandine Schaeffer has a background in oceanography and is leading the development of the bluebottle prediction tool, as part of UNSW's Bluebottle Watch program. She has come to be fascinated with these biological oddities, and admits that there is still a lot that scientists don't know about bluebottles.

For example, nobody really knows exactly how, when and where they breed, and how the four different zooids develop to make a new colony.

"Bluebottles are difficult to study in their natural environment and are challenging to sustain in artificial settings like labs," says Dr Schaeffer, who is part of UNSW’s Centre for Marine Science and Innovation.

"Unlike fish or sharks, which can be tagged in the wild to study their movement, bluebottles are too light and would sink immediately. So we need to be creative to understand their displacement."

Arguably one of the strangest morphological traits of the bluebottles is that they're left or right handed – which may sound odd when talking about animals with no limbs!

The 'handedness' refers to which side the pneumatophore, or gas-filled sail, leans. Half of all bluebottles have a sail that leans to the left, and half to the right. Why would this be?

“It’s an evolutionary feature that maximises survival,” Dr Schaeffer says.

“Because the bluebottle doesn’t swim, it can only drift where sea currents and wind take it. The sail being on the left or the right determines the direction the bluebottles drift. This means the wind – unless it's very strong – will blow half the population ashore where they will likely die, while the other half live on to sting another day.”

Understanding how the wind affects bluebottles is crucial to developing a tool that predicts their presence on beaches. So the UNSW team made some replicas fitted with radio tracking equipment to see how bluebottles travel from out at sea.

The UNSW team researching bluebottle movements – along with colleagues from the Mediterranean Institute of Oceanology in France and the University of Toulon– 3D-printed eight replica bluebottles out of plastic and silicone, each fitted with internal satellite tracking technology.

To allow for the special equipment on board, the replicas were considerably larger than the usual size of bluebottles that wash up on Australian shores – about 15cm long.

But one part of the design was crucial to help the scientists understand how the replicas interact with the elements: half had left-leaning floats, while the other half leaned to the right.

This would test the theory that left or right-aligned sails on bluebottles had an impact on where bluebottles drifted in the ocean.

The radio devices in each replica emitted a signal every five minutes that allowed the scientists to track their location in real time – invaluable data that would inform calculations in the bluebottle prediction tool.

On a calm day in January 2024, the research team dropped eight of the replicas in the water 5kms off the coast of Botany Bay. They watched as the 20km/h wind separated the lefties from the righties.

(Interestingly, when the wind blows stronger than 30km per hour, the bluebottles get blown en masse in the same direction, with the sails unable to resist powerful gales.)

In one experiment, they left two overnight in the ocean – Dr Schaeffer says the devices are too valuable to risk losing too many at once. One of them ended up on Bondi Beach, and when the team went to collect it, they noticed lots of actual bluebottles had also washed up.

In another experiment, a device washed up on Palm Beach and was picked up by a dog. Luckily the dog’s owner rang the number printed on it and the team was able to retrieve it.

So how will experiments like this help?

Dr Schaeffer says the data will be used to work backwards along the devices’ journeys to observe the way they react to the different wind, current and swell forces.

“We're trying to understand how they move with ocean currents, winds and waves, and which conditions bring them to shore. Once we know that we can use forecasts from the Bureau of Meteorology about ocean currents, wind fields and swell data. And the idea is to have a statistical model that is fed with these environmental variables, which will allow us to make predictions about the likelihood of bluebottles being on a particular beach.”

There's just one little problem. It's near impossible so far to predict the population dynamics and where the next swarm of stingers is.

"We're using machine learning to analyse bluebottle sting and observations data to pinpoint when and where the bluebottles reach the Australian coast. And we're using oceanographic models to understand where the bluebottles begin their journey," Dr Schaeffer says.

The group is working with Surf Life Saving Australia who will start testing it, once the modelling is ready. The plan is to integrate the tool into the Beach Safe app once it's operational.

“If this works, then hopefully we will be able to have some kind of warning on the beach the day before – for example, at Bondi Beach there’s a 70 per cent chance there’ll be bluebottles the next day.”

Recommended resources

• UNSW's Bluebottle Watch program
• UNSW's Beach Safety Research
• SLSA's Beach Safe resource and app