Assessing the vulnerability of commercial bivalves to intensifying atmospheric heatwaves in coastal ecosystems.

Heatwaves are expected to intensify and become more frequent throughout the 21st century, posing significant threats to coastal ecosystems and socio-economically important species. Shellfisheries based on intertidal and shallow subtidal infaunal bivalves such as Ruditapes decussatus, Ruditapes philippinarum, Venerupis corrugata, and Cerastoderma edule are of significant socio-economic importance in Europe, particularly in the Galician Rías Baixas (NW Spain). This study evaluates how future atmospheric heatwaves may compromise the thermal dynamics of these four commercially important bivalves in the Ría de Arousa. Global atmospheric and oceanic climate data from CMIP6 were downscaled using the WRF and Delft3D-FLOW models. The WRF model was used to characterize atmospheric heatwaves for the period 2025-2099 under the SSP2-4.5 and SSP5-8.5 pathways, while the Delft3D-FLOW model calculated bottom water temperatures under the SSP5-8.5 pathway during the most intense future atmospheric heatwave. Thermal exposure on bivalves was evaluated using a 1D sediment heat transport model. The analysis of atmospheric heatwaves revealed a total of 88 events projected throughout the 21st century, with an increase of the frequency, duration, and intensity over time, particularly during summer months. A significant increase in bottom water temperature in the estuary's inner areas was simulated under the most intense future atmospheric heatwave, driven by extreme air temperature and calm winds. The species V. corrugata and C. edule experienced the longest exposure to high temperatures, linked to their shallower burrowing depths and lower thermal tolerance, while R. decussatus and R. philippinarum remained unaffected during the atmospheric heatwave simulated. These findings highlight the vulnerability of certain bivalve species to intensifying heatwaves, which could lead to greater socioeconomic consequences.