Mediterranean macroalgal forests under threat: the effects of ongoing climate change and design of restoration methods

Macroalgal forests represent some of the most productive and biodiverse habitats on Earth. In the Mediterranean Sea, species of the genus Cystoseira sensu lato dominate the well-preserved subtidal rocky habitats where they form complex macroalgal communities. However, since the end of the twentieth century, they have suffered important and widespread regressions across the Mediterranean Sea, mainly due to habitat destruction, changes in water quality and overgrazing by sea urchins. As a result, they are often replaced by simpler and less productive communities. The return to pre-disturbed conditions does not necessarily imply the natural recovery of Cystoseira s.l. stands, being active restoration the only feasible alternative to assist the recovery of these populations. Nowadays, climate change, especially gradual warming and acute marine heatwaves (MHWs), represents a global threat for macroalgal forests. In this context, while no studies have reported evidence of warming impacts for Cystoseira s.l. forests, taking into account that Cystoseira s.l. populations have been historically impacted and the expected climate change scenarios for the Mediterranean Sea, it is of paramount importance to know how climate change can affect these species. The results of this thesis show the potential effects of warming on populations of shallow Cystoseira s.l. species, pointing out the relevance of local environmental factors and processes ultimately defining the response of these populations to global trends of climate change. Moreover, we also offer new and promising tools to locally restore these habitats. Overall, our findings are relevant in order to inform local-scale management and conservation plans for safeguarding the persistence of these Mediterranean macroalgal forests ; Els boscos de macroalgues representen un dels hàbitats més productius i diversos del planeta. A la Mar Mediterrània, les espècies del gènere Cystoseira sensu lato dominen els fons rocosos submareals de les àrees ben preservades, on formen ...