Forests formed by brown algae of the genera Cystoseira, Ericaria and Gongolaria (Cystoseira forests) create unique seascapes at shallow depths of Southern European seas, particularly the Mediterranean. The great ecological, economic and social significance of these ecosystems and the services that they provide are widely recognised. Their relevance is acknowledged by several international conventions and directives (Bern Convention, Barcelona Convention, EU Habitats Directive). The need of their surveillance and conservation are recognized by the International Union for the Conservation of Nature (IUCN), the Mediterranean network of Marine Protected Areas and the European Union (within the Marine Strategy Framework Directive). In the last decades, however, Cystoseira forests have undergone a major decline in the whole Mediterranean basin, due to the high sensitivity of these algae to some anthropogenic stressors acting at local/regional scales but widespread throughout the basin. There is general consensus that the impact of these stressors will be further exacerbated by the effects of climate change (mainly in the form of heat waves, and extreme episodic events). The development of effective strategies for the conservation of the residual Cystoseira forests based on new tools for their monitoring is now of fundamental importance. The present project has been designed to provide these tools and assist environmental policy makers in the management of Cystoseira forests. Its main objectives are 1) identify Cystoseira species and/or populations with high significance from the conservational point of view, for which special protection measures are necessary, and assess their tolerance thresholds to selected environmental stressors; and 2) defining accurately the health status of Cystoseira forests based on quantitative metrics. These objectives will be achieved by combining large-scale phylogenomic and population biology studies, field and laboratory experiments testing the responses of Cystoseira species/populations to selected stressors, and field surveys investigating many variables at community level. Major elements of novelty in the project will be the use of Unmanned Aerial Vehicles for the mapping of Cystoseira forests, large-scale characterization of the microbiomes and the environmental DNA associated with these communities, large-scale phylogeographic characterization of forestforming Cystoseira species and active involvement of stakeholders in research activities and post-hoc monitoring of Cystoseira forests. Key outputs of the project will include new, user-friendly monitoring tools for large-scale use by stakeholders involved in environmental management. The project will be implemented by a consortium of 9 research groups from 6 EU Member States that have gained great familiarity with these ecosystems in the course of previous projects and whose expertise covers a wide range of disciplines in marine biology.