“Gone with the wind”: Fatty acid biomarkers and chemotaxonomy of stranded pleustonic hydrozoans (Velella velella and Physalia physalis)

•Chemotaxonomic characterization of Velella velella and Physalia physalis regarding their FA profile.•Comparison of the abovementioned species FA with those from other cnidarian orders.•V. velella exhibit higher levels of symbiotic dinoflagellates markers (18:3n-6, 18:4n-3 and 20:5n-3).•P. physalis displayed higher levels of bacterial markers (odd-numbered, branched and 18:1n-7 FAs).•Presence/absence of endosymbionts, specific FAs and latitudinal habitat were the drivers for the distinction among groups.

Marine pleustonic species such as the hydrozoans Velella velella and Physalia physalis, are known to drift in the world's oceans driven by winds, currents and tides. Here we present the first chemotaxonomic characterization, based on the fatty acid (FA) profile, of these two charismatic oceanic species that thrive in the interface layer between air and the water column in adult stages. Moreover, we compared their FA profiles with those from other representative cnidarian orders (Rhizostomeae, Anthomedusae, Siphonophorae, Alcyonacea, Scleractinia, Helioporacea and Pennatulacea). Velella velella and P. physalis mainly differed in the presence of symbiotic dinoflagellates markers (18:3n-6, 18:4n-3 and 20:5n-3 polyunsaturated FAs), present in higher percentage in the former, and bacterial markers (odd-numbered, branched and 18:1n-7 FAs), which were more representative in the latter. When comparing these species' FA profiles with the ones of other cnidarians orders, the presence/absence of endosymbionts and of specific FAs (tetracosapentaenoic and tetracosahexaenoic acids) as well as the latitudinal habitats were the main drivers for the distinction between groups.