Physalia spp., or Man-of-War, drifts in tropical and subtropical waters, transported by ocean surface conditions. Its unique drifting behavior, influenced by dimorphism (left or right-handedness), complicates stranding predictions. Specifically, the quantification of the influence of the wind on Physalia spp. movements remains an open question, although essential for accurate Lagrangian tracking models. We investigated the wind effect on Physalia spp. by testing 3D-printed replicas in a controlled wind flume. Our findings reveal that under weak winds, left- and right-handed specimens drift symmetrically apart, aligning with strandings observed near Sydney, Australia. As wind speed rises, the drift angle decreases exponentially from approximately 40°, eventually stabilizing near a downwind direction in high winds. On average, the drift speed is 1.7 % of the wind speed. Variations in body shape impact drift angles and stability, adding stochasticity to paths. The proposed empirical relationship might advance knowledge of Physalia spp. sources, distribution and pathways.
Keywords: 3D printed replicas; Bluebottle; Dimorphism; Portuguese Man-of-War; Stings; Wind-wave flume.
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