This dataset contains the data and code associated to the manuscript "Population collapse of habitat-forming species in the Mediterranean: a long-term study of gorgonian populations affected by recurrent marine heatwaves."

Understanding the resilience of temperate reefs against the increasingly frequent marine heatwaves (MHWs) requires exploring the recovery capacity of their key habitat-forming species. Here, we show that, in a Mediterranean highly enforced Marine Protected Area established more than 40 years ago, the habitat-forming octocoral populations that were affected by the 2003-MHW have not recovered after 15 years. Contrarily, they have followed collapse trajectories that have brought them to the brink of local ecological extinction. Since 2003, impacted populations of the red gorgonian Paramuricea clavata (Risso, 1826) and the red coral Corallium rubrum (Linnaeus, 1758) have followed different trends in terms of size structure, but a similar progressive reduction in density and biomass. Concurrently, recurrent MHWs were observed in the area during the 2003-2018 study period, what may have hindered any chance of populations recovery. Since Mediterranean habitat-forming octocorals play a unique role in the functioning of coralligenous assemblages, our results underpin the great risk that recurrent MHWs pose for the long-term integrity and functioning of these emblematic temperate reefs.