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Marine microbes play fundamental roles in nutrient cycling and climate regulation at a planetary scale. The field of marine microbial ecology has experienced major breakthroughs following the application of high-throughput sequencing and cultureindependent methodologies that have pushed the exploration of the marine microbiome to an unprecedented scale. This chapter overviews how the advances in gene- and genome-centric approaches as well as in culturing and single cell physiological methodologies in conjunction with global oceanographic circumnavigation expeditions and long-term time series are fueling our understanding of the biogeography, temporal dynamics, functional diversity, and evolutionary processes of microbial populations. We discuss how the joint effort of all those integrative approaches will help to boost our knowledge of the marine microbiome to reach a predictive understanding of how it is going to evolve in future scenarios.

The Alboran Sea is the first Mediterranean basin where the modified Surface Atlantic Waters and the subsurface Mediterranean waters meet and mix before they continue their path either towards the Mediterranean or towards the Atlantic Ocean, respectively. Due to its close location to the Strait of Gibraltar, the hydrodynamics of the Alboran Sea and also its biogeochemical features are strongly influenced by the high variability of the physical processes that govern the mixing and exchange of water masses at the Strait of Gibraltar. Likewise the own variability of the Alboran Sea hydrodynamics, driven by the path of the Atlantic jet and the upwelling of subsurface Mediterranean waters richer in nutrients, stimulates the growth of phytoplankton and enhances primary production in this basin during large part of the year, which makes of the Alboran Sea the most productive basin of the Mediterranean Sea. The enhanced production also gives rise to intense remineralization processes in the water column that affects the dynamics of nutrient and dissolved oxygen in the basin. This chapter reviews the biogeochemical features of the Alboran Sea and their spatial and temporal dynamics as well as its effects on the marine planktonic community, focusing on the coupling between physics, biogeochemistry, and phytoplankton productivity. The objective is to provide a general overview on how physical forcing determines nutrient dynamics in the water column and how this regulates the variability of chlorophyll-a and primary production in this basin. Likewise, it also addresses the spatial and temporal variability of primary production in this basin and how phytoplankton regulates the biogeochemical dynamics of nutrients in the Alboran Sea. The chapter also examines the initiatives and the current stage of knowledge related to the potential impact of climate change on the Mediterranean Sea.

49 pages, 15 figures, The seafloor of the Alboran Sea reflects its complex tectonic, sedimentary, and oceanography dynamics as a consequence of the geological context, involving interaction between the Eurasian and African plates, and oceanographic context, as it is where the Atlantic and Mediterranean waters meet. Their physiography has a semi-enclosed configuration characterized by two margins (the Spanish Iberian and North Africa—mostly Moroccan margins) enclosing deep basins. Tectonic activity is mainly attested by folds and faults that predominantly affect the central and eastern seafloor sectors, as well as numerous seamounts and fluid-flow features (pockmarks, mud volcanoes, and diapirs) that dot the seafloor. The sedimentary and oceanographic processes allow us to distinctly define two principal environments in the Alboran Sea: the shallow proximal margin (continental shelf); and the deep distal margin (continental slope and base of the slope) with the adjacent sub-basins. The shelf mostly comprises prodeltaic and infralittoral prograding wedges, with local bedform fields, submarine valleys, and wave-cut terraces. Coastal and fluvio-marine sedimentary processes, acting since the last glacial period, are responsible for these features. The deep marine environment is characterised by the ubiquity of contourites, whose continuity is interrupted by turbidite systems, canyons, and landslides. The alongslope action of the Mediterranean waters and their interfaces with the Atlantic water has been the main process governing transport, seafloor reworking, and sedimentation of contourites. Mass-movement processes are responsible for the formation of: (1) turbidite systems—turbidity flows and mass flows were dominant during the last glacial sea-level lowstand, evolving to dilute gravity flows during present interglacial high stand; and (2) landslides—the main triggering factors comprising over-steepening, seismicity, under consolidation due to overpressure by interstitial fluids, stratigraphy, and high sedimentation rates. Locally, still-undetermined biological activity in the Spanish and coral activity in the Moroccan margin generated fields of mounded bioconstructions. The seafloor morphology of the Alboran Sea offers interesting clues for assessing the main potential geological hazards, with tectonic seismicity and landslides (as well as their related tsunamis) being some of the most important potential hazards affecting coastal populations. In addition, the seafloor morphology in combination with assemblages of habitat-forming species enables habitat identification and mapping, This work was supported by the following Spanish projects INCRISIS, DAMAGE (CGL2016-80687-R AEI/FEDER), FAUCES (CTM2015-65461-C2-1-R) and ALSSOMAR S2S (CTM2017-88237-P), RNM 148 and RNM 328 groups of Junta de Andalucía, MONCARAL and RIGEL projects (Instituto Español de Oceanografía) Marboro cruises. Likewise, this study was supported by the French program Actions Marges and the EUROFLEETS program-SARAS cruise (FP7/2007-2013; 228344)

Marine megafauna typically include large pelagic sharks, sea turtles, seabirds, and marine mammals. These megafauna are mainly associated with pelagic ecosystems through which they undertake long-distance migration. The Alboran Sea connects the Atlantic Ocean and Mediterranean Sea and is thus a relevant hotspot for marine megafauna. In this area, the overlap between various human activities—such as marine traffic or fisheries on the north and south coasts—and pollution entails the capture or mortality of marine megafauna. We review the main research and findings on marine megafauna in the Alboran Sea and discuss research approaches that could provide suggestions for the effective management of large marine ecosystems.

Cold-water corals are recognised as a key component of Mediterranean deep-sea ecosystems but the knowledge of their associated biodiversity is still limited. To date, the fauna associated to the Central Mediterranean cold-water coral habitats is the best known (e.g. the cold-water coral provinces of Santa Maria di Leuca, Bari canyon and Strait of Sicily) but such knowledge should be extended to the whole Mediterranean Basin. The combined biodiversity censed so far for Mediterranean cold-water coral habitats and those of adjacent areas (Strait of Gibraltar-Gulf of Cádiz) includes a conspicuous number of species (ca. 520 spp.) with a high representation of sponges (ca. 90 spp.), polychaetes (ca. 90 spp.), cnidarians (ca. 80 spp.), bryozoans (ca. 75 spp.), crustaceans (ca. 60 spp.), molluscs (ca. 50 spp.), fishes (ca. 50 spp.), echinoderms (ca. 20 spp.) and brachiopods (7 spp.). Most species are not univocally linked to cold-water corals, but they benefit from the complex and diverse microhabitats provided by them. There is a clear need to continue the investigation of Mediterranean cold-water coral habitats to fully document the faunistic inventory, biogeographic connections and functions of the many species connected to such emblematic ecoystems of the deep-sea.