Abstract

In the context of global warming, seagrass species exhibit various adaptive responses to rising temperatures, including the migration to deeper (cooler) areas. However, moving to deeper habitats does not only result in reaching lower temperatures, but also to be exposed other critical environmental factors that vary with depth. For instance, light availability decreases with depth, which can impact the metabolism of primary producers, and constrain their depth distribution. Previous research has modelled seagrass distribution based on lethal thermal limits under optimal light conditions. Other studies have projected a future vertical habitat contraction of seagrass meadows assuming similar thermal tolerance across water depth. Nevertheless, the interaction between light and temperature requires further investigation, as they may interact and impact the thermal performance of the organism, including their thermal thresholds, and consequently, their vertical distribution. To investigate this interaction, we conduced mesocosms experiments using the three seagrass species (Cymodocea nodosa, Posidonia oceanica and Zostera noltei) present in the Mediterranean Sea. Thermal performance curves were used to assess the seagrass growth, survival and metabolic rates at varying light intensity, which was used as a proxy for depth. Understanding the interaction between environmental factors, such as light intensity and temperature, on performance and thermal thresholds is crucial for enhancing predictions regarding vertical distribution of species and developing effective conservation strategies for marine ecosystems under climate change scenarios.