Sponge assemblages on continental shelves and slopes around the world have been known about for centuries.However, due to limitations of the traditional sampling systems, data about individual sponge species ratherthan assemblages have been reported. This study characterizes sponge assemblages over a wide bathymetricrange (~50–350 m depth) and covering the entire continental shelf and the upper slope of the Menorca Channel,an area soon to be declared a Marine Protected Area (MPA) as part of the Natura 2000 Network. Quantitativeanalysis of 85 video-transects (a total linear distance of 75 km), together with representative collections toconfirm species identifications, allowed us to discriminate six major assemblages. Differences in the assemblagesmainly corresponded to differences in substrate type and depth. On the inner continental shelf, a semi-scia-philous Axinellid assemblage dominated the rocky outcrops. Maërl beds on the inner continental shelf weredominated byHaliclona (Reniera) mediterranea, whereas the horny spongeAplysina cavernicolaand several otherhaliclonids mostly dominated maërl beds and rocky substrates of the outer shelf. Soft sediments on the shelfbreak hosted a monospecificThenea muricataassemblage, whereas rocky substrates of the shelf break werecharacterized by a mixture of encrusting, columnar and fan-shaped sponges. Finally, the upper slope wasdominated byHamacantha (Vomerula) falculaand the hexactinellidTretodictyum reiswigi. Overall, sponge di-versity showed its highest values above the shelf break, plummeting severely on the upper slope. Despite thisdiversity decrease, we found very high densities (> 70 ind./m2) of sponges over vast areas of both the shelfbreak and the upper slope.
Spain - Mediterranean Sea