Coupling habitat-specific temperature scenarios with tolerance landscape to predict the impacts of climate change on farmed bivalves

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.

Predicting organismal response to marine heatwaves using dynamic thermal tolerance landscape models

Marine heatwaves (MHWs) can cause thermal stress in marine organisms, experienced as extreme 'pulses' against the gradual trend of anthropogenic warming. When thermal stress exceeds organismal capacity to maintain homeostasis, organism survival becomes time-limited and can result in mass mortality events. Current methods of detecting and categorizing MHWs rely on statistical analysis of historic climatology and do not consider biological effects as a basis of MHW severity. The re-emergence of ectotherm thermal tolerance landscape models provides a physiological framework for assessing the lethal effects of MHWs by accounting for both the magnitude and duration of extreme heat events. Here, we used a simulation approach to understand the effects of a suite of MHW profiles on organism survival probability across (1) three thermal tolerance adaptive strategies, (2) interannual temperature variation and (3) seasonal timing of MHWs. We identified survival isoclines across MHW magnitude and duration where acute (short duration-high magnitude) and chronic (long duration-low magnitude) events had equivalent lethal effects on marine organisms. While most research attention has focused on chronic MHW events, we show similar lethal effects can be experienced by more common but neglected acute marine heat spikes. Critically, a statistical definition of MHWs does not accurately categorize biological mortality. By letting organism responses define the extremeness of a MHW event, we can build a mechanistic understanding of MHW effects from a physiological basis. Organism responses can then be transferred across scales of ecological organization and better predict marine ecosystem shifts to MHWs.