Global warming is severely threatening Mediterranean coastal lagoons’ integrity, with potentially severe consequences for their functioning and ability to provide ecosystem goods and services.

The Mediterranean green crab, Carcinus aestuarii, is a key component of Mediterranean lagoons trophic webs, also supporting local artisanal fisheries. Thus, assessing future changes in its distribution under progressively warmer lagoon conditions appears urgent.

We quantified the thermal performance of C. aestuarii by measuring respiration rates (RR) across a temperature gradient ranging from 8 to 38°C. Thermal performance curves (TPCs) were used to estimate its thermal habitat suitability (THS) probability, which was then projected onto seasonal temperature maps of four Sardinian coastal lagoons under reference conditions (2017–2022) and future climate scenarios (RCP 4.5 and RCP 8.5 for 2050).

RR increased with temperature up to an optimum temperature of 29.2°C (0.21 mgO₂ h⁻¹ g⁻¹ WW) and sharply declined thereafter, with complete mortality occurring at 38°C (CT_max). Current THS probability projections revealed strong seasonal variability, with low suitability levels during winter and optimal conditions during summer across all lagoons. Under both future warming scenarios, the THS probability increased across all seasons, suggesting expanded thermally favorable conditions for the crab adults.

Overall, our results indicate that a moderate warming might enhance habitat suitability for the adult crabs, especially during the winter reproductive season. However, this apparent benefit should be interpreted cautiously. Projected increasing marine heatwaves frequency and reduced thermal heterogeneity caused by warming may expose the crab populations to episodic thermal stress, while the higher thermal sensitivity of early life stages could constrain the species recruitment success, potentially offsetting the habitat suitability gains projected for adults. We conclude that, preserving hydrodynamic connectivity and thermal refugia may be crucial for sustaining the persistence of this species and, considering its ecological importance, the lagoon ecosystem functioning as a whole.