Terrain, oceanographic, and biological factors underlying the development of Mediterranean coastal animal forests

Marine Animal Forests (MAFs) form three-dimensional seascapes and provide substrate and shelter for a variety of species. We investigated the fine-scale distribution pattern of three habitat-forming species of the coastal Mediterranean MAFs: Eunicella cavolini, E. singularis and Paramuricea clavata, and assessed the influence of terrain, oceanographic, and biological factors on their distribution and the formation of MAFs in the central-northern Tyrrhenian Sea. Species presence and abundance were obtained through seafloor HD imagery and were combined with terrain and oceanographic parameters extracted from remote sensing data using distance-based linear modeling (DistLM) and generalized additive model (GAM). The three studied species occurred in all the study areas, with marked differences in their abundance and distribution across the different sites and habitat type, in relation to seafloor characteristics. Specifically, positive relationships emerged between the density of colonies and terrain parameters indicative of high seafloor complexity, such as slope and roughness, as well as the number species structuring MAFs. A clear niche separation for the three species was observed: E. cavolini and P. clavata were reported on coralligenous reefs, and in areas where the seafloor complexity may enhance hydrodynamics and transport of organic matter, while E. singularis was observed on red algal mats at shallower depths. A better understanding of the ecology of these gorgonians, as well as of the drivers determining MAFs formation, represent the first step toward the conservation of these threatened habitats which are currently poorly protected by management and conservation plans.