Biodiversity plays an important role in maintaining and improving ecosystem functioning, thereby increasing ecosystem stability. There is convincing evidence suggesting that autogenic ecosystem engineers like gorgonians enhance biodiversity at the local scale (Idjadi & Edmunds, 2006), primarily through changes produced in the environmental conditions of their surroundings. Their three-dimensional physical structures increase the number of ecological niches available, which in turn seem to favour megafaunal species richness. However, very little empirical data has ever been provided. Gorgonian density and size relationship with the diversity of associated megafauna was explored in two very contrasting regions: the pristine eastern Weddell Sea in Antarctica and Cap de Creus in NW Mediterranean. Monoespecific patches of the gorgonians Thouarella variabilis in Antarctica and Eunicella cavolinii in the Mediterranean Sea were evaluated using Remotely Operated Video (ROV) images, recorded on the continental shelf at depths below 100 metres. The fauna associated with T. variabilis was more diverse than that of E. cavolinii, with 108 taxa recorded in the Weddell Sea and 78 in the Mediterranean region. The number of species and diversity rapidly increased with increasing gorgonian densities at both sites, until a maximum was reached. In terms of community structure, there was also a switch in the associated fauna with changes in gorgonian density. In contrast, gorgonian size only showed a positive correlation to species richness and diversity only in the Antarctic region. The results of the present study highlight the role of gorgonians in the diversity and the structuring of benthic communities, indicating their importance when designing management plans to protect the marine benthos. At the same time, this study shows that ecosystem engineers like gorgonians, which act as foundation species, could be used to restore shelf and deep-sea ecosystems that have been altered by human activities. (PDF) The role of gorgonians as engineering species in the diversity and composition of benthic communities. Available from: https://www.researchgate.net/publication/336775061_The_role_of_gorgonians_as_engineering_species_in_the_diversity_and_composition_of_benthic_communities [accessed Feb 25 2020].