The occurrence and density of 3 cold-water coral (CWC) species (Madrepora oculata, Lophelia pertusa and Dendrophyllia cornigera) were investigated in the Cap de Creus canyon (northwestern Mediterranean) by conducting and analysing 22 video survey transects. Species distribution patterns were also investigated at 3 spatial extents (km, 100s of m and m) across 3 of the transects using spatial statistics. Additionally, the locations of snagged benthic long-line fishing gear were logged across these 3 transects. Video surveys were carried out by both remotely operated vehicles (ROVs) and the JAGO manned submersible. CWCs were present in 15 of the 22 survey transects, predominantly those covering areas with hard substrate (boulders or hardrock outcrops). M. oculata was the most abundant CWC species in the survey transects, whereas L. pertusa and D. cornigera were much more sparsely distributed, with only isolated colonies observed in the majority of transects. M. oculata showed a significant contagious distribution pattern across the analysed transects, with several scales of spatial pattern and patch size being detected, whereas L. pertusa and D. cornigera were not found in sufficient numbers to apply spatial statistics. Different covariance patterns were found across the transects between snagged fishing gear and the presence of M. oculata. Further investigation of this relationship and the level of hazard posed by long-line fishing to M. oculata colonies is required prior to development of a protective management strategy.

[1] Posidonia oceanica is a widespread coastal Mediterranean seagrass which accumulates in its subsurface large quantities of organic material derived from its roots, rhizomes and leaf sheaths embedded in sandy sediments. These organic deposits may be up to several meters thick as they accumulate over thousands of years forming the matte, whose high content in organic carbon plays a major role in the global ocean carbon cycle. In this study, very highresolution seismo-acoustic methods were applied to image the subsurface features of a P. oceanica seagrass meadow at Portlligat (Cadaqués, Girona, Spain), in the NWMediterranean Sea. Our findings yield fresh insights into the settling of the P. oceanica meadow in the study area, and define with unprecedented detail the potential volume occupied by the matte. A strong reflector, located from 4.3 to 11.7 m depth, was recognized in several seismoacoustic profiles as the substratum on which P. oceanica first settled in the study area. A 3D bathymetric model of this substratum allowed us to reconstruct the Portlligat palaeo-environment prior to the settling of P. oceanica, which corresponded to a shallow coastal setting protected from the open sea. A core drilled in the meadow at Portlligat revealed the presence of a 6 m thick dense matte composed of medium to coarse sandy sediments mixed with plant debris and bioclasts. Radiocarbon datings revealed a constant accretion rate of the matte of about 1

Recently acquired high‐resolution multichannel seismic profiles together with bathymetric and sub‐bottom profiler data from the external part of the Gulf of Cadiz (Iberia‐Africa plate boundary) reveal active deformation involving old (Mesozoic) oceanic lithosphere. This area is located 180 km offshore the SW Iberian Peninsula and embraces the prominent NE‐SW trending Coral Patch Ridge, and part of the surrounding deep Horseshoe and Seine abyssal plains. E‐W trending dextral strike‐slip faults showing surface deformation of flower‐like structures predominate in the Horseshoe Abyssal Plain, whereas NE‐SW trending compressive structures prevail in the Coral Patch Ridge and Seine Hills. Although the Coral Patch Ridge region is characterized by subdued seismic activity, the area is not free from seismic hazard. Most of the newly mapped faults correspond to active blind thrusts and strike‐slip faults that are able to generate large magnitude earthquakes (Mw 7.2–8.4). This may represent a significant earthquake and tsunami hazard that has been overlooked so far.

Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are associated with prominent topographic features and can produce large earthquakes. Here we show the first evidence of a major tectonic structure in its initial-stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Combining bathymetric and seismic reflection data, together with seismological analyses of the 2016 M w 6.4 earthquake offshore Morocco – the largest event ever recorded in the area – we unveil a 3D geometry for the AIFS. We report evidence of left-lateral strike-slip displacement, characterise the fault segmentation and demonstrate that AIFS is the source of the 2016 events. The occurrence of the M w 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model of the inception and growth of a young plate boundary fault system.

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Scleractinian cold-water coral (CWC) reefs are key habitats for benthic fauna as they enhance spatial heterogeneity and biodiversity. Understanding their environmental and ecological dynamics has therefore important implications for biodiversity conservation. This is especially true for the Mediterranean Sea, where living cold-water coral reefs are rare. In this study, we present a quantitative analysis of the CWC assemblages from Cabliers Coral Mound Province, located in the Alboran Sea (westernmost Mediterranean). The province extends for 25 km, with some mounds rising up to 140 m from the surrounding seafloor and being partly topped by living CWC reefs. The observed megabenthic species were quantified through video analysis of three Remotely Operated Vehicle (ROV) dives (280 -485 m water depth) and their distribution was related to mound geomorphic characteristics and seafloor terrain parameters, extracted from a high-resolution Autonomous Underwater Vehicle (AUV) multi-beam bathymetry. The pronounced abundance and size of scleractinian CWCs among the observed assemblages, makes Cabliers the only known coral mound province in the Mediterranean Sea with currently growing reefs. Within these reefs, several recruits and juveniles of the sebastid Helicolenus dactylopterus were observed, confirming the use of such habitats as nursery grounds by some commercially valuable fish species. The qualitative comparison between the fauna of Cabliers and Atlantic coral mounds suggest that the number of species associated with CWC mounds worldwide is even higher than previously thought. This finding has important implications for the conservation and management of CWC habitats in different geographic regions.

14 Cold-water corals (CWCs) are widely distributed in the entire Alboran Sea (western Mediterranean Sea), but only 15 along the Moroccan margin they have formed numerous coral mounds, which are constrained to the West and 16 the East Melilla CWC mound provinces (WMCP and EMCP). While information already exists about the most 17 recent development of the coral mounds in the EMCP, the temporal evolution of the mounds in the WMCP was 18 unknown up to the present. In this study, we present for the first time CWC ages obtained from four sediment 19 cores collected from different mounds of the WMCP, which allowed to decipher their development since the last 20 deglaciation. Our results revealed two pronounced periods of coral mound formation. The average mound 21 aggradation rates were of 75-176 cm kyr -1 during the Bølling-Allerød interstadial and the Early Holocene, only 22 temporarily interrupted during the Younger Dryas, when aggradation rates decreased to <45 cm kyr -1 . Since the 23 Mid Holocene, mound formation significantly slowed-down and finally stagnated until today. No living CWCs 24 thrive at present on the mounds and some mounds became even buried. The observed temporal pattern in 25 mound formation coincides with distinct palaeoceanographic changes that significantly influenced the local 26 42 3. Internal waves play a dominant role in controlling mound formation.43 4. Coral mound formation stagnated since the Late Holocene. 44 45 3