Holothurian diversity and distribution in the central Cantabrian Sea and the Avilés Canyon Systems (Bay of Biscay)

Currently, due to the global change and biodiversity loss, the knowledge of the species taxonomy and distribution is more than ever crucial. Especially in areas as the Avilés canyon systems (ACS), which is a Site of Community Importance (SCI) included in the Natura 2000 Network. A check-list of the echinoderm species belonging to the class Holothuroidea (a group that has been less studied and with scarce literature available) from the ACS was carried out, as well as a characterization of the holothurian fauna and its distribution. Samples were collected from both the continental shelf, slope and bathyal zones of the Asturian central coast (COCACE cruise, 1987–88), and the slope, bathyal and abyssal areas of the Avilés canyon systems (BIOCANT cruises, 2012–13). The identification of the species was based on morphological traits as well as on the observation of the microscopic calcareous ossicles extracted from different parts of the holothurian body. One hundred and seventy four specimens, belonging to 35 species of the five orders of the class Holothuroidea, were identified. Multivariate analysis allowed the differentiation of four main assemblages, which corresponded to abyssal plain, lower continental slope, upper continental slope, and continental shelf. Depth was the main structuring agent. Holothurian species richness was higher in deep-sea areas, the abyssal plain being the area with the highest number of species found