Filling gaps in the Webbnesia marine diversity: The Madeiran sponge fauna

Despite few pioneering works in the late XIX and early XX century, the poriferan fauna of Madeira has remained mostly unexplored until today, Madeira being one of the least studied eastern Atlantic archipelagos in terms of its sponge diversity. After a thorough analysis of both new material collected by SCUBA diving as well as a literature research, 140 sponge species are known to occur in the Madeira archipelago. From the 56 species identified by both collected material and pictures, approximately 60% (34 species) are new records for the Archipelago. These 34 new records were found associated with littoral rocky substrates and, to a lesser extent, caves, rhodolith beds and wrecks, within a depth range of 10 to 35 m depth. Our records also contain several Mediterranean species that have not been previously recorded in the North Atlantic, several North-east Atlantic species whose presence in Madeira marks their southernmost limit of occurrence, as well as elements from the subtropical West African fauna. Amongst the new additions to its sponge fauna there are the first records of Homomscleromorpha, with at least three Oscarella species noted, as well as a new species of Hemimycale (Demospongiae, Poecilosclerida). Yet, this is still an underestimation of Madeira’s real sponge diversity. Data on Madeiran sponge fauna is still skewed towards shallow and littoral habitats, with other less accessible environments, such as caves, rhodolith beds or the deep sea, remaining largely unexplored. Similarly, complex poriferan groups (e.g. calcareans, haplosclerids, tetractinellids, hymedesmids) have only been partially studied, and their true diversity remains unknown. Finally, due to a lack of prior baseline it is difficult to conclude if some newly recorded species are non-indigenous, range-expanding or simply previously overlooked native species. However, it is now clear that two previously thought non-indigenous species, Mycale (Carmia) senegalensis and Prosuberites longispinus are in fact native to the Archipelago, their prior status as non-indigenous arising from the lack of prior confirmation of their presence outside of port facilities.