Habitat and identification of scyphozoan polyps in Bages-Sigean lagoon (France)

Polyps are important stage in the medusozoan jellyfish life cycle, but the ecology of wild populations is still poorly understood. For some species, like Rhizostoma pulmo, polyps have never been reported in the wild. The Bages-Sigean lagoon is a Mediterranean, semi-enclosed lagoon with seasonally abundant Aurelia coerulea and R. pulmo medusae. Given its semi-closed nature and because ephyrae are commonly observed, it is likely that the polyps of both species reside in the lagoon. Our study aimed to characterize the polyp species distribution for this lagoon by performing snorkeling surveys of the potential polyp substrates, such as wood, concrete, buoys and bivalves. We observed polyp colonies at five sites, all on the underside of floating polypropylene docks despite the diversity of available substrates. Identification of the jellyfish species was performed in two ways: by strobilation then development of the ephyrae in aquaria, and by DNA sequencing of the collected polyps. All five sites produced A. coerulea medusae, but we were unable to locate polyps of R. pulmo despite surveying substrates that the planulae settle on under laboratory conditions. This study underscores the need to improve our ability to locate polyps in the wild by expanding laboratory studies to include more species, increasing sampling efforts and substrates in the field, and applying new methods (e.g., eDNA, hydrodynamic modeling).