Artificial Light At Night (ALAN) is a globally widespread anthropogenic stressor in coastal areas, affecting physiology and behaviour of several species, with cascading impacts on community and ecosystem level processes. However, little is known about how habitat structure modulates these effects. The sea urchin Paracentrotus lividus is an ecologically important species that exhibits behavioural changes when exposed to ALAN. It commonly inhabits both Posidonia oceanica meadows and rocky shores, two habitats that may differ in sheltering conditions (including those related to ALAN) and food availability. This study investigates the role of these two habitat types in modulating the effects of ALAN on the behaviour and physiology of P. lividus. We hypothesized that the response to ALAN would be more intense in rocky habitat than in P. oceanica habitat, due to less sheltering and food availability. An experiment was conducted in two 7-day runs around the new moon using six 500-L mesocosms, each containing six P. lividus individuals. Each mesocosm contained either rocky or P. oceanica habitats and it was equipped with LED systems that simulate a natural photoperiod and the ALAN condition (9.47 lux). Six mesocosms across the two runs (three per habitat type) were treated with a nocturnal dark regime and the other six with the ALAN scenario, in a fully crossed design with three replicates per condition. Righting behavior and attachment strength were assessed after five days. Grazing rate was quantified over four consecutive days and nights as the biomass loss of pre-weighed dried kelp. At the end of each run, respiration rate was estimated by incubating individual sea urchins in sealed chambers and measuring oxygen loss for 1 h using an oxymeter. Results will be discussed within the framework of the role of habitat structure in mitigating ALAN impacts on a key Mediterranean species.