Disturbance duration governs mortality risk while cumulative energetic deficit shapes reproduction in Mediterranean mussels.

Marine mussels are foundation species and ecosystem engineers increasingly exposed to marine heatwaves, hypoxic episodes and food limitation, yet apparently similar events can generate sharply different outcomes among populations. Here I test whether this variation can be explained by the interaction between disturbance duration, cumulative energetic deficit and internal energetic state. Using a Dynamic Energy Budget model for the native Mediterranean mussel Mytilus galloprovincialis and the invasive Brachidontes pharaonis across four environmental forcing scenarios, I decompose reproductive performance into the probability of reaching maturity and reproductive investment conditional on maturation. At equal cumulative energetic deficit, the uninterrupted duration of feeding suppression governs mortality risk and overall reproductive performance, whereas accumulated deficit governs how much surviving individuals invest in reproduction. Survival declines nonlinearly across a narrow duration range whose position is ordered by the reserve margin maintained under undisturbed conditions. Vulnerability therefore depends on the coincidence between event duration and energetic state, which varies with local food conditions, season and life stage. The native species, operating closer to its starvation boundary, is consistently more vulnerable than the invader, which maintains a larger reserve buffer. These results identify reserve margin as a measurable candidate predictor of recruitment failure and mortality risk. More broadly, they show why cumulative exposure metrics alone may miss the temporal continuity that drives survival loss. This individual-level mechanism provides a testable explanation for why apparently comparable coastal disturbances can generate uneven recruitment failure and contribute to spatially heterogeneous mass mortality in mussel populations.