Distribution and vulnerability of the endemic deep-water kelp Laminaria rodriguezii in a warming Mediterranean SeaBroad-scale Spatial Patterns

Uxue Moreda¹, Raul Golo¹, Jorge Santamaría¹, Emma Cebrián¹

¹Centre d’Estudis Avançats de Blanes (CEAB-CSIC), Spain

Kelps are large, brown, canopy-forming macroalgae that typically thrive in sublittoral shallow areas within temperate and cold-water regions. However, the Mediterranean Sea hosts unique deep-water kelp forests constituted by the endemic species Laminaria rodriguezii. Despite the ecological importance of L. rodriguezii as a habitat-forming species, knowledge about its distribution, ecological limits, and vulnerability to environmental changes remains limited. This lack of knowledge implies that in general, its state of conservation and threats are poorly known. However, in the last decades, bottom trawling has degraded this habitat in several regions, and as a cold-water species, the distribution of L. rodriguezii may be further restricted by ongoing Mediterranean warming. Here, we estimate the potential distribution of L. rodriguezii and asses its vulnerability under future warming scenarios. To this end, we first developed a habitat suitability map based on more than 150 historical records of L. rodriguezii in the Mediterranean Sea. Then, we conducted a mesocosm experiment to evaluate the thermal performance of L. rodriguezii at eight different temperatures using specimens from the Balearic Islands. Finally, this data was integrated into a modelling approach to predict distribution changes under the RCP 8.5 warming scenario by 2050 across the Mediterranean Sea. Preliminary results indicate that high temperatures negatively affect the performance of L. rodriguezii leading to biomass loss and suggesting that future warming may further restrict its distribution range and increase its vulnerability. However, deeper areas with minimal warming could act as climate refugia, preserving populations and providing sanctuary for other species, although such populations would always be limited by low light availability. These findings highlight the need to protect these critical habitats from anthropogenic stressors and ensure their resilience to future climatic challenges.