Climate change is predicted to have detrimental impacts on sessile invertebrates, including sponges, which cannot change their location or environment. Among the various physiological implications, elevated temperature could sever a sponge's association with its microorganisms, which may subsequently lead to sponge mortality. Mesophotic coral ecosystems have been suggested to play a major role as refugia for coral species that are unable to tolerate the changing conditions in the shallow waters. In this study we examined the response of the sponge-holobiont Diacarnus erythraeanus, a widespread Red Sea sponge, to elevated temperature from the shallow and mesophotic reef.