The California mussel (Mytilus californianus) is ecologically important in the intertidal zone and an understanding of their responses to stress may help predict how populations respond to environmental perturbation. Assimilating food into cellular energy is necessary to support a physiological stress response and studies show that previous diet may be vital for mussels responding to stressors, such as acute heat shock. Furthermore, our lab has shown that sirtuins (protein deacylases) also affect thermal tolerance in mussels and may be a link between diet and thermal sensitivity. Mussel’s gills are integral for feeding and gill activity is often used to assess overall metabolic status. As such, we evaluated changes in ciliary beat frequency (CBF) in M. californianus following an acute heat shock and sirtuin inhibition in mussels acclimated in tidal simulators to 20°^C or 30°^C aerial temperatures during low tide and a low or high food ration. CBFs were video recorded on excised gill segments during high tide periods 48 h before and after heat shock on a temperature-controlled slide (10X). Mean CBF from video was determined using Cilia Beat Analyzer package (Matlab). We found CBF decreased after an acute heat shock and further decreased if mussels were also exposed to sirtuin inhibitors. There was a significant 3-way interaction between food ration, acclimation temperature, and sirtuin inhibition. This suggests a complex relationship between thermal history and food ration on the ability of mussels to respond to thermal stress and a potential role of sirtuins as metabolic stress regulators.