Climate change generates side-effects with direct and indirect ecological repercussions that are often difficult to predict. Among main ecological side-effects at local level, community compositional shift is one among the most difficult to predict. An example is the case of the shift from a seagrass-dominated to an algae-dominated state where multiple effects due to climate and local biotic interaction factors such as grazing due to the sea urchin’s action usually drive the transition from high- to low complexity habitats. While this kind of shift is well-investigated in the Mediterranean Sea, mechanisms driving it are less known as those driven by functional traits dealing with the species-specific thermal performances. Temperature indeed drives all activities at individual level including the strong link between metabolism and feeding (grazing) rates. Thus, investigating the species-specific thermal window of grazers involved in the ecosystem shifts illustrate the role of temperature in ecological processes, increasing our ability to predict ecosystem shifts under current increasing temperature. Here, thermal tolerance of purple sea urchin Paracentrotus lividus was investigated and specimens of P. lividus were sampled from Sicilian subtidal sites and 19 different temperatures, between 8°C and 37°C, were tested, using respiration rates as a proxy of individual metabolism. P. lividus showed a left-skewed curve, with a Topt at 29°C, classifying P. lividus as a thermo-tolerant species, by now living in the Mediterranean Sea very often near-to or over the measured thermal optimum. Such a basal functional information may result crucial when assessing and predicting the role of grazers in reversing the ecosystem state as provides the extent of the thermal field of action of grazers under the current increasing temperature of water masses in the Mediterranean Sea.