The influence of morphology on deep-sea coral distribution: habitat suitability modelling of bamboo corals (Octocorallia: Scleralcyonacea: Keratoisididae) in the NE Atlantic

Deep-sea corals are vulnerable marine ecosystems that require conservation and protection actions, but the extreme environment in which they grow makes it difficult to obtain sufficient data to understand their distribution. Species distribution models could be a very effective tool for investigating the occurrence of these benthic communities, but it is necessary to delve deeper into the factors that influence these distributions to obtain accurate and reliable models to be used for management policies. The aim of this study was to investigate the influence of colony morphology on coral distribution, specifically of individuals of the octocoral family Keratoisididae. The software MaxEnt was used to build species distribution models for the three morphologies (unbranched, branched 2D, branched 3D) observed in the NE Atlantic, and then distribution maps were generated in ArcGIS. The models of the three morphologies showed overall a good performance but were not representative of reality, and this might be linked to sampling bias. The occurrence maps obtained from the models highlighted that the three groups have a different distribution pattern, probably linked to the different preferences for the environmental conditions in which to settle. By observing how environmental variables influence the occurrences of the morphologies, it emerged that branched 3D keratoisidids preferred different environmental conditions compared to branched 2D and unbranched bamboo corals, especially with regard to the variables linked to geomorphology (bathymetric position index, rugosity, slope). It has also been demonstrated that the genus Acanella, which is part of the branched 3D group, settles in different environmental conditions. Due to the limitations that generally characterize deep-sea investigations, it was not possible to completely accept the initial hypothesis, but the need for further studies regarding the influence of morphology on coral distribution was highlighted.