Links Between Lagrangian Connectivity, Thermal Thresholds and Genetic Structure in the Floating Marine Siphonophore Physalia

Aim To investigate whether genetically distinct species of Physalia differ in dispersal behaviour and environmental exposure, and to assess the role of large‐scale wind–ocean transport in shaping their genetic structure. Location Tropical and subtropical oceans where Physalia strandings and distributions overlap. Time Period One‐year drift simulations, based on recent genetic sampling between 2006 and 2023 and reanalysis datasets. Major Taxa Studied Physalia (Portuguese Man O′ War/Bluebottle), a colonial hydrozoan genus comprising five genetically distinct species. Methods We combined genetic identification of 125 individuals from five lineages with numerical Lagrangian particle backtracking. Drift trajectories were simulated using oceanic and atmospheric reanalysis fields, with an experimentally derived drift parameterization that accounts for Physalia 's asymmetric morphology and wind‐driven motion. Connectivity metrics derived from simulated transport were compared with observed genetic differentiation. Results Drift simulations revealed strong lineage‐specific differences in dispersal and temperature exposure. Average sea surface temperature along drift paths ranged from 15°C for Physalia minuta to 28°C for Physalia mikazuki . Genetic differentiation within lineages was significantly associated with dispersal connectivity: the combination of geographic distance and Lagrangian transport explained up to 57% of variance in genetic distance. Main Conclusions Wind–ocean transport is a key driver of both environmental exposure and genetic structure in Physalia . Differences in dispersal pathways expose lineages to distinct thermal regimes, with implications for ecology and biogeography. As climate change alters wind fields, currents and ocean temperatures, connectivity and thermal habitats will shift in lineage‐specific ways, potentially reshaping the distribution and evolutionary trajectories of Physalia species.