Bluebottle Watch

As part of an international initiative supported by the Australian Research Council and led by the University of New South Wales (UNSW), Sydney, a collaborative team from MIO (UTLN) and OSU Pytheas recently embarked on an offshore expedition along the Australian coast in late Janu-ary 2024.

This undertaking, known as the BluebottleWatch project, focuses on unravelling the dynamics of Physalia physalis (called ‘Bluebottles’ in Australia), a colony consisting of various functionally distinct individuals, including floaters, tentacles, feeding polyps, and reproductive polyps, all intricately interdependent. The recurring mass strandings of Bluebottles on Australian shores, coupled with the painful stings inflicted on beachgoers, under-score the critical importance of this investigation.

Physalia physalis

The primary objective of the project is to elucidate the mechanisms governing the transport and beaching patterns of Bluebottles, influenced primarily by wind, currents, and waves, from both empirical and theoretical perspectives, in order to make predictions for the future and warn the public.

As part of Natacha Bourg's thesis, under the supervision of  Anne Molcard (MIO-Université de Toulon) and Amandine Schaeffer (UNSW), 3D models constructed from scans of real Bluebottles underwent testing in the Luminy wind tunnel (LASIF), with the essential tech-nical support from Rémi Chemin (UTLN) and Christopher Luneau (CNRS). The ABS and silicone model had to satisfy three crucial criteria: realistic shape, stability, and buoyancy.

The investigation into the impact of varying wind intensities on the velocity and trajectory of Bluebottles with different characteristics (left-handed, right-handed, short, or low sails) yielded preliminary experimental findings consistent with previous research: Bluebottles veer at an angle that diminishes with increasing wind forcing (to the right of the wind for left-handed specimens and vice versa). Subsequently, these models were scheduled for field testing.

A batch of 3D-printed Bluebottles, equipped with GPS and satellite communication systems, was assembled, transported to Sydney, and deployed at sea.

The marine conditions proved highly variable within a single day and across successive days, providing ample opportunities for Bluebottles releases under varied weather and sea states.

All Bluebottles models were successfully retrieved, whether from the sea or from shoreline stranding events. The analytical phase of these observations is currently underway, aiming to formulate a Lagrangian model depicting Bluebottle movement in terms of speed and direction related to winds and currents.

This model will be seamlessly integrated into oceanic circulation simulations to un-derstand the origin and variability of Bluebottles. The team (photo 6 +6b) is stands ready to repli-cate their experiments in the wind tunnel and the Mediterranean Sea, utilizing the same BB mod-els now housed at the MIO facilities.

Bluebottles models printed from 3D scans

First experimental result: the Bluebottle sails at an angle that decreases with wind intensity (to the right of the wind if left-handed and vice versa).