Lisandro Benedetti-Cecchi1
1University of Pisa, Italy
Global warming is a main threat to marine life, affecting all levels of biological organization, from individual organisms to entire assemblages. Measuring temperature at the scales at which organisms perceive their environment is essential to understand the ecological impacts of warming and to accurately predict future responses. This is particularly true for sessile species that have no escape when facing an unfavorable environment. Yet, most studies rely on remotely sensed macroclimate data to characterize ocean temperatures and to train models of species distribution, whereas a focus on microclimates has remained elusive in the marine realm. Here, I provide a high resolution characterization of the three-dimensional thermal environment of macroalgal forests using a simple plastic frame harboring 27 temperature loggers arranged in three vertical layers. Replicated measurements conducted in the Tuscan Archipelago (north-western Mediterranean) between 2022 and 2024 showed significant temperature variation in the range of 0.5 to 4 °C among loggers 50-100 cm apart and at temporal scales of hours to days. The canopy provided a cooler understorey environment compared to the water column, but, surprisingly, the tip of the algal canopy was warmer than the water column during the central hours of the day, although with variation among deployments. About 20% of the instances in which the water column temperature qualified as a marine heatwave, the temperature underneath the algal canopy was below the threshold. These results reveal a large degree of temperature heterogeneity at previously unresolved spatial and temporal scales and call for more rigorous microclimate research in rocky reef ecology. By averaging out local temperature variation, macroclimate data can only provide crude approximations of the thermal environment, possibly obscuring the key local processes that drive large-scale responses of marine biodiversity to global warming.
Biography
Lisandro Benedetti-Cecchi (LBC) is Professor in Ecology at the University of Pisa. LBC uses marine coastal plants and animals as experimental model systems to address fundamental ecological questions, including the causes and consequences of loss of biodiversity, the ecological impacts of climate change and the role of Marine Protected Areas for the conservation of marine life. He received the International Temperate Reef Symposium award for lifelong contribution to marine science in 2019.