Blowin’ in the wind: Onshore winds drive the occurrence of bluebottles (Physalia spp.) at east Australian beaches

Bluebottles ( Physalia spp.) are a floating siphonophore that inhabit coastal waters and can become stranded on beaches around the world. They inflict painful stings on beachgoers which can place significant strain on surf life saving personnel. With little capacity for active (directed) swimming, their movement and distribution is driven by physical atmospheric and oceanographic processes and other biological processes (e.g., reproduction). This study combines multiple long term and spatially extensive datasets documenting their occurrence along the east coast of Australia with high resolution oceanographic and atmospheric reanalysis products to investigate (1) how the occurrence of beached bluebottles relates to public safety concerns (i.e., sting rates) and (2) potential drivers of occurrence (in terms of beaching, stings per swimmers, or abundance of left- or right-handed bluebottles). We find that the risk of being stung increases rapidly as the number of beached bluebottles increases, suggesting that bluebottles on the beach is a good indicator that they are also in the water. Wind appears to be the primary driver of their occurrence, with onshore winds ( ≈ 20–180°) leading to the highest likelihood of occurrence, especially under stronger wind speeds ( ≥ 8 m s −1 ) with patterns consistent with the theoretical and experimentally determined drift trajectories for bluebottles. Finally, we demonstrate some ability to predict occurrence and make recommendations for further development of a predictive model to assist stakeholders in mitigating the adverse effects of large swarms at beaches. • A relationship between bluebottle beaching and beachgoer stings is established. • This provides context to interpret the public health risk of mass beaching events. • Multiple datasets indicate wind is the primary driver of bluebottle occurrence. • We provide a foundation to develop predictive tools to forecast beachgoer risk.