Understanding and predicting bluebottles along the coast
Many Australians have had a painful bluebottle sting, yet little is known about bluebottles and what brings them to the coast. This project will shed new light on bluebottle dynamics, pathways, and distribution of bluebottle beachings.
We will use an innovative combination of lab work, ocean surveys, statistical and hydrodynamic modelling to fill knowledge gaps and ultimately develop the first bluebottle risk prediction tool for our popular beaches in partnership with Surf Life Saving Australia (SLSA).
Only recently, the bluebottle was recognised the same species as the Portuguese Man of War in the Atlantic: Physalia physalis (Global Biodiversity Information Facility).
It is not a jellyfish, but a fascinating colonial organism (called a Siphonophore) found predominantly in tropical and subtropical regions. In the Atlantic, Physalia is larger and more venomous and believed to live for around a year, although this is still being confirmed (Munro et al 2019).
The bluebottle does not swim, but floats at the ocean’s surface and trails a stinging tentacle up to 3m below the surface. The gas-filled ‘pneumatophore’ that floats on the ocean surface (1-15cm) acts as a ‘sail’ that is subject to wind forces. The sail is oriented to the left or right of the body of tentacles, resulting in individual bluebottles being either right-handed or left-handed. Why? Well, since the sail/float orientation plays a role in determining bluebottle drift due to the wind direction, right and left-handed individuals will not all drift in the same direction. This well-designed morphological and behavioural adaptation is thought to ensure half the population avoid potential death if beached on the shore.
If you see a bluebottle on the beach, first don’t touch its tentacles! They can sting even when it’s dead.
Please take a photo and upload it to iNaturalist platform, ideally using a top view and with an indication of the length of the float (include your finger in the photo or estimate the length as shown with the red line in the figure below.
Finally, if you have a scientific mind, join our iNaturalist project, where you can add an estimate of the abundance, the size, and the handedness of the bluebottle.
Is it right or left-handed? When pointing forward, away from you, with the float at the top, the dark blue bulge of the tentacles is to the right of the float for right-handed bluebottles, or to the left of the float for left-handed bluebottles.
There are so many things we can do nowadays with a 3D printer!
We are working to create realistic silicone bluebottle floating models to perform movement experiments in a lab. The movement of the bluebottle is unique, in that it is determined by an interplay of morphological characters and environmental drivers.
Previous research from the 1960s used observational studies at sea to explore the unusual drifting angle of bluebottles relative to the wind speed and direction (Totton and Mackie, 1960). This research concluded that Physalia was horizontally transported (a.k.a. advected) ±40 degrees downwind for weak winds, with this angle decreasing for stronger winds.
We want to explore this more extensively in a lab (and under lots of different conditions) using a controlled wind / wave tunnel facility. Moreover, we have access to flumes and tunnel where we can change the beach profiles for different wave conditions or generate current and winds.
We can record the drift angle and speed of the bluebottle float, depending on:
Have you ever seen a Bluebottle in an aquarium? The answer is most likely no since no one has managed to keep them alive for more than a couple of months.
This is the challenge we are taking on in collaboration with Sea World and the Griffith Sea Jellies Research Laboratory: including the development of a bluebottle-specific tank to add to the beautiful Sea Jellies illuminated exhibit at Sea World.
We will also use this new tank for scientific experiments. In particular, we want to study the behaviour of the bluebottle in response to changes in winds and temperature, such as the rolling behaviour, the contraction of the float, and coiling of the tentacle.
Satellite tags are not yet small and light enough to attach to bluebottles. Most of the knowledge about the pathways of passive material in the ocean (e.g. larvae or plastics) comes from drifting buoys experiments, or from numerical simulations.
Numerical particle tracking uses estimates of wind and ocean current speed and direction at the surface to move a particle around. Our ‘particle’ has similar characteristics to a bluebottle. We use purpose build bluebottle module (Lee et al, 2022 a,b), to estimate how the wind and ocean currents move the particle at each time step.
The source of bluebottle swarms is unknown. Particle tracking can also be reversed to "backtrack" the bluebottle like particles, and hence finally understand where they come from. Are the Tasmamian bluebottles coming from the Great Barrier Reef? The answer is coming soon!
We are monitoring the presence / absence of bluebottles on the beach during summer months, and how it varies from one day to another, and one beach to another. Recording the abundance, shape, size, and handedness of the bluebottles will also help us to understand their population dynamics. Ultimately, we will link the arrival of bluebottles to shore to environment variables and create a statistical model to forecast their distribution along the coast.
Attaching a satellite tag to a bluebottle without affecting its floatability is not yet achievable. What we can do, however, is to track other drifters to understand how objects move at the interface between the ocean currents and the wind.
In the future, we will add a GPS to our bluebottle-shaped drifters and deploy them within a bluebottle armada to track it in real-time, and compared to routinely used ocean drifters. Stay tuned.
Bourg, N., A. Schaeffer, P. Cetina-Heredia, J C. Lawes & D. Lee (2022). Driving the blue fleet: Temporal variability and drivers behind bluebottle (Physalia physalis) beachings off Sydney, Australia. PLOS One
Lee, D., Schaeffer, A., & Groeskamp, S. (2021). Drifting dynamics of the bluebottle (Physalia physalis). Ocean Sci.,Vol 17, October 2021.
Munro, C., Vue, Z., Behringer, R., and Dunn, C.: Morphology and development of the Portuguese man of war, Physalia physalis, Sci. Rep.-UK, 9, 15522, https://doi.org/10.1101/645465, 2019