Margalida Monserrat1,2, Steeve Comeau2, Jana Verdura1, Samir Alliouane2, Guillaume Spennato1, Fabrice Priouzeau1, Gilbers Romero1 and Luisa Mangialajo1
1 Université Côte d’Azur, CNRS, ECOSEAS, France, 2 Sorbonne Université, CNRS, Laboratoire d’Océanographie de Villefranche, Villefranche-sur-Mer, France
Forest-forming macroalgae can be particularly sensitive to environmental conditions, especially during early life stages. As a result, climate change could lead to a worldwide loss of marine forests and the lack of evidence of natural recovery highlights the need for imminent restoration actions. Therefore, it is essential to consider the role played by abiotic and biotic factors when assessing the outcome of future restoration actions. However, not much is known about the effects of ocean warming and acidification on Cystoseira s.l. species. These drivers can also affect its associated understory species, mainly crustose coralline algae, likely playing a role in the recruitment of later successional species. We studied the interactive effects of ocean warming, acidification and species facilitation (i.e. presence of crustose coralline algae) on recruits of Cystoseira compressa to assess the potential of restoring this species under climate change. Recruits were maintained at 24, 28 and 32°C, at ambient (pHT = 8.07) and low pH (pHT = 7.8) and in the presence or not of the crustose coralline algae Neogoniolithon brassica-florida. We demonstrate that ocean warming, acidification and the presence of the coralline algae negatively affect the recruitment of C. compressa. The density of recruits was lower under high temperatures and low pH, whereas the size was negatively affected by the temperature increase but positively affected by the low pH. While new techniques recently opened the door to the restoration of marine forests, our results show that climate change has to be considered to achieve long-term restoration success and ensure population sustainability.