The integration of ecological and evolutionary data is highly valuable for conservation planning. However, it has been rarely used in the marine realm, where the adequate design of marine protected areas (MPAs) is urgently needed. Here, we examined the interacting processes underlying the patterns of genetic structure and demographic strucuture of a highly vulnerable Mediterranean habitat-forming species (i.e. Paramuricea clavata (Risso, 1826)), with particular emphasis on the processes of contemporary dispersal, genetic drift, and colonization of a new population. Isolation by distance and genetic discontinuities were found, and three genetic clusters were detected; each submitted to variations in the relative impact of drift and gene flow. No founder effect was found in the new population. The interplay of ecology and evolution revealed that drift is strongly impacting the smallest, most isolated populations, where partial mortality of individuals was highest. Moreover, the eco-evolutionary analyses entailed important conservation implications for P. clavata. Our study supports the inclusion of habitat-forming organisms in the design of MPAs and highlights the need to account for genetic drift in the development of MPAs. Moreover, it reinforces the importance of integrating genetic and demographic data in marine conservation.

Ocean warming, caused by climate change, is critically impacting marine coastal ecosystems. Benthic organisms, such as anthozoans, are increasingly submitted to high temperatures that cause massive mortalities in tropical and temperate seas. To broaden our understanding of their response to thermal stress, we tested the putative role of reproductive maturity and sex in the susceptibility of the Mediterranean red gorgonian, Paramuricea clavata, to high temperatures. We experimentally compared the response to thermal stress of sexually immature (i.e., juveniles) versus mature individuals (i.e., adults), and of males versus females. Colonies' response was firstly assessed by measuring the percentage of tissue area exhibiting necrosis. Then, the reproductive output (i.e., fertility, size, and number of gonads) of both sexes was characterized. When compared to juveniles, adults showed a significantly higher percentage of necrosis, suggesting that during the reproductive period they are more vulnerable to high temperatures. Males and females showed a similar percentage of tissue damage and a significant decrease in their reproductive output. However, females' reproduction was more impacted, suggesting that females are more susceptible to thermal stress than males. A differential energy investment in reproduction may be the underlying cause of the observed responses. Adults invest a large proportion of their energy budget in reproduction; hence, they have fewer resources available to cope with stress, compared to juveniles. A similar situation seems to apply to females, with respect to males. Considering the current ocean-warming trend, our results imply that the long-term viability of shallow populations of long-lived anthozoans may be jeopardized in the future. This study reveals potential demographic consequences of warming that go beyond its associated increment of mortality rates. Given the important ecological role of many anthozoan species, these results can help better predict the future effects of climate change on coastal ecosystems.