17 pages, 10 figures, 2 tables, supplementary data https://doi.org/10.1016/j.ecss.2024.109042.-- Data availability: The georeferenced raster layer containing the predicted distribution of E. cavolini along the whole study area obtained from the restricted RF model (Fig. 6b) can be downloaded from the SEANOE scientific open data portal using the following link: https://doi.org/10.17882/103094, Extensive knowledge exists about the ecology of gorgonian species dwelling in coastal areas of the Mediterranean, but less information is available regarding populations found in deep circalittoral and bathyal environments. In recent years, the use of marine imaging technology has led to the discovery of dense coral gardens below SCUBA depths. This is the case of Eunicella cavolini (Koch, 1887) populations dwelling on the continental shelf off Cap de Creus (northwestern Mediterranean), an area included in a Site of Community Importance (SCI) of the Natura 2000 Network. We characterized the environmental niche of this species using a combination of density data extracted from 60 underwater video transects (80–400 m depth) and a set of environmental factors of a geomorphologic, oceanographic and human nature. Populations of E. cavolini develop within a restricted combination of environmental conditions, predominantly in areas of the mid continental shelf (95–110 m depth) characterized by a mixture of substrates (gravels, pebbles and rocks) with intermediate yearly average bottom current velocities (0.11–0.13 m s−1) and where no records of bottom trawling activity were registered in the years prior to the surveys. The species forms dense aggregations that average 6–8 col·m−2, with local high-density peaks above 15 col·m−2. Areas suitable for the development of E. cavolini were modelled by means of a Random Forest algorithm, which predicted that an area extending over 14 ha could potentially host populations with densities over 5 col·m−2. Bottom current velocity emerged as the most important factor determining the spatial distribution of the species, followed by depth and presence of rocks. Colony height measurements indicated that populations are dominated by small-to-medium sized colonies, with average colony height positively correlated with gorgonian density. The reduced average colony height observed might respond to the strong bottom current regime characteristic of Cap de Creus, but also to the increased likelihood of larger colonies to be captured as by-catch by trammel nets, a common type of fishing gear used in the area. This study provides relevant information about the ecology of E. cavolini populations dwelling on deep circalittoral habitats, useful for policymakers when formulating specific management measures to foster the conservation of this species inside the SCI. Additionally, the data provided could assist on the restoration actions already taking place in Cap de Creus, and be used as baseline data to monitor the evolution of E. cavolini populations through time once management plans are implemented, The collection of images used for this study were funded by the European project LIFE + INDEMARES (LIFE07/NAT/E/000732) and the Spanish project Acciones Complementarias nº CTM2007-28758-E/MAR. Numerical simulations for the bottom current models were performed using HPC resources from the CALMIP platform (French region Occitanie) under grant P09115. [...] This work acknowledges the AEI ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). CD-C acknowledges the financial support received by the EU funded projects Life + Indemares (LIFE07/NAT/E/000732) and ENPI ECOSAFIMED (ENPI CBC MED 2007–2013) and by the FCT-IP Project UIDP/05634/2020, With funding form the Spanish government through the "Severa Ochoa Centre of Excellence" accreditation (CEX2019-000928-S)., Peer reviewed

This dataset provides a raster layer (.img format) with the predicted distribution of the gorgonian Eunicella cavolini (Koch, 1887) on the continental shelf and submarine canyon off Cap de Creus (NW Mediterranean), an area included in a Site of Community Importance (SCI) of the Natura 2000 Network. The algorithm Random Forest (RF) was used to model areas suitable for the development of the species based on a combination of species density data extracted from 60 underwater video transects (80 to 400 m depth) and a set of environmental factors of a geomorphologic, oceanographic and human nature. The RF model predicted the presence of the species (densities of at least 1 col·m-2) in 1,061 ha along the whole modelled area, with 14 ha potentially hosting gorgonian densities above 5 col·m-2 and 4.9 ha with densities exceeding 10 col·m-2. The variability explained by the model was 70.1%, although a cross-validation assessment indicated that the variability explained could be lower, denoting some degree of spatial autocorrelation of the data within the underwater dives. Based on the percentage increase in mean squared error of the model used for predictions, the most important variables determining the likelihood of finding high-density patches of E. cavolini in the study area were average bottom current velocity, depth and rugosity of the seafloor (calculated as TRI, Terrain Ruggedness Index). This study provides relevant information about the spatial distribution of E. cavolini inside a recently declared marine protected area of NW Mediterranean, which could be used by policymakers when formulating specific management measures for the conservation of this species within the SCI.

This dataset is related to the article “Environmental niche, spatial distribution and size structure of shelf-dwelling populations of the gorgonian Eunicella cavolini (Koch, 1887) in NW Mediterranean” submitted to Estuarine, Coastal and Shelf Science by Dominguez-Carrió et al., which contains further information on how the data were obtained and processed., The development of the Random Forest (RF) model was funded by the European project LIFE+ INDEMARES (LIFE07/NAT/E/000732). The biological data used to feed the RF model was obtained through several surveys funded by the European project LIFE+ INDEMARES (LIFE07/NAT/E/000732) and the Spanish project Acciones Complementarias nº CTM2007-28758-E/MAR. The bathymetric data for the continental shelf was provided by the Spanish Fisheries General Secretary, and acquired in the frame of the ESPACE, DeepCoral and LIFE+ INDEMARES projects. Multibeam data for the submarine canyon was acquired by the University of Barcelona, AOA Geophysics and the Institute of Marine Sciences (ICM-CSIC). The bottom current model used to run the RF model was performed using HPC resources from the CALMIP platform (French region Occitanie) under grant P09115, with the SYMPHONIE model distributed by the SIROCCO group (https://sirocco.obs-mip.fr). VMS data was provided by the General Directorate of Fisheries Management of the Spanish Ministry of Agriculture, Food and Environment (MAGRAMA). The authors would like to thank the crew of the research vessel García del Cid and all the scientists and technicians who assisted during the different oceanographic cruises, as well as Gavin Newman (ROV pilot) and the members of the JAGO Team Jürgen Schauer and Karen Hissmann (Geomar, Kiel) for the acquisition of the video footage. This work acknowledges the AEI ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). CD-C acknowledges the financial support received by the EU funded projects Life+ Indemares (LIFE07/NAT/E/000732) and ENPI ECOSAFIMED (ENPI CBC MED 2007-2013) and by the FCT-IP Project UIDP/05634/2020., With funding form the Spanish government through the "Severa Ochoa Centre of Excellence" accreditation (CEX2019-000928-S)., Peer reviewed