Back from presumed local extinction: the case of Sargassum hornschuchii C.Agardh (Fucales: Heterokontophyta) in the Spanish Mediterranean

We report on a new record of Sargassum hornschuchii C.Agardh in the Spanish Mediterranean after having no reports for more than a century. Sargassum hornschuchii was found in a deep-water rocky bottom offshore Menorca together with the kelp Laminaria rodriguezii Bornet and the rockweed Ericaria zosteroides (C.Agardh) Molinari & Guiry. We make an accurate morphological description and provide pictures of the specimens collected. This new record puts into question the assignment of the IUCN “extinct” category for deep-water rare macroalgae as they can go unnoticed for a long time. This also highlights the need to protect remote deep-water spots where biodiversity can still be flourishing.