Recent advances in understanding the ecology and functioning of submarine canyons in the Mediterranean Sea

The Mediterranean Sea, a land-locked and highly vulnerable sea, is one of the world's marine basins with the highest concentrations of deep-sea canyons. The knowledge of the biology and ecology of Mediterranean canyons has increased notably in the last 20 years. The present paper aims at summarizing the new knowledge presented in the Special Issue of Progress in Oceanography entitled "Ecology and functioning of Mediterranean submarine canyons", where multi-disciplinary studies in marine ecology, biology, physical and biological oceanography, sedimentology, microbiology and bioinformatics, provide an unprecedented advancement in the knowledge of these complex systems. The investigated canyons cover a broad range of Mediterranean regions, from the Polcevera and Bisagno canyons along the Ligurian margin (NW Mediterranean Sea) to the Gioia and Petrace canyons in the Gulf of Gioia (Ionian Sea), and the Tremestieri and Messina canyons in the Messina Strait, or the Dohrn Canyon in the Gulf of Naples (Tyrrhenian Sea), including also the Ban Canyon (Southern Adriatic Sea) and the Cap de Creus Canyon (Gulf of Lion). This issue also furnishes crucial information on biotic components so far neglected in previous studies such as the microbial components, the zooplankton and fish assemblages. We can find here original information on pelagic and benthic food webs, the role of viruses and single-celled prokaryotic and eukaryotic microbes in driving biogeochemical processes, and the threats caused man-made pollutants (including litter) along with their effects on the deep-sea biota. The contents of this issue evidence the vulnerability of marine canyons to anthropogenic impacts and represent a step forward in the identification and understanding of the links between biological processes and geological and physical and chemical conditions in submarine canyons. The outputs of these studies will stimulate future research, enabling a better comprehension of the functioning of these systems and of the needs and benefits of their conservation.