Extreme weather events, such as heatwaves, are becoming increasingly frequent, long-lasting, and severe as global climate change continues, shaping marine biodiversity patterns worldwide. Increased risk of overheating and mortality across major taxa have been recurrently observed, jeopardizing the sustainability of ecosystem services. Molecular responses of species, which scale up to physiological and population responses, are determinant processes that modulate species sensitivity or tolerance to extreme weather events. Here, we analysed the whole-body proteome of the intertidal ragworm Hediste diversicolor (Müller, 1776), a keystone species in estuarine ecosystems and an emergent blue bio-resource, to long-lasting heatwaves (24 ºC vs 30 ºC for 1 month). We hypothesized that this species is phenotypically plastic and thus able to acclimate to heatwaves by inducing cytoprotective pathways and modulating energy metabolism to enhance its thermal tolerance and maintain survival. To test these hypotheses, worms were exposed to control (24 ºC) and a +6 ºC increase in water temperature (30 ºC) for a month, after which they were collected for whole-body proteomic (after 28 days of exposure) analysis. Concomitantly, fatty acid analysis (after 28 days of exposure) and cumulative survival, upper thermal tolerance limits and wet weight (after 30 days of exposure) were compared between control and heatwave exposed worms.