Distribution and diversity of mesopelagic fauna on seamounts of the Madeira-Tore complex (Northeastern Atlantic)

Mesopelagic organisms play an important role in the vertical carbon flux through diel vertical migrations. The mesopelagic fauna of three NE Atlantic seamounts (Gorringe Bank, Josephine and Seine) and surrounding oceanic waters were sampled. Echogram scrutiny suggests a diel vertical migration of the mesopelagic fauna. Muggiaea atlantica and Meganyctiphanes norvegica were caught at almost every station and thus, appeared to be ubiquitous. Several taxa were only caught in open oceanic stations (e.g. Lampanyctus alatus, Deosergestes corniculum and Acanthephyra purpurea) whereas others appeared uniquely in the vicinity of the seamounts (e.g. Lophogaster sp., Systellapsis pelucida and most of the cephalopod species). Multivariate analyses, based on presence–absence data, indicated significant differences in the mesopelagic community structure among the different seamounts, and between oceanic and seamount waters. Higher species richness was found in oceanic waters compared to seamounts. No significant relationship was found between the environmental variables salinity and fluorescence and the biological data. Even so, the values of these oceanographic parameters over the seamounts are different from those in oceanic waters. Knowledge of diversity and distribution of mesopelagic fauna will improve our understanding of the pelagic realm.