Growth disturbances in bivalve shells are widely observed in both fossil and modern species, yet the conditions and mechanisms driving their formation remain unclear. Through controlled experiments on Mimachlamys nobilis, we demonstrate that abrupt intra-annual temperature fluctuations (≥5 °C) induce shell growth disturbances by altering the energy budget, diverting resources from shell growth to stress responses. Under ≥5 °C fluctuations (Groups C and D), 67 % of the individuals exhibited shell thinning, reduced growth rates, and formed growth disturbance lines (Groups C and D), whereas <5 °C fluctuations (Groups A and B) caused disturbances in only 12 % of the cases. These bivalve growth disturbances serve as a sensitive bio-indicator of short-term temperature fluctuations, providing a novel tool for reconstructing intra-annual level marine climatic fluctuations in deep time.