Simple Summary: Climate change is significantly impacting the structure and functioning of marine communities through temperature rise and the repeated occurrence of temperature spikes and marine heat waves. The present study investigated the metabolic responses of the sponge Chondrilla nucula, an important component of benthic ecosystems in the Mediterranean Sea, to temperature. Organisms were exposed to six different temperatures ranging from 15 to 32 degrees C, and respiration and clearance rates were measured. The results revealed temperature-dependent effects on both traits. Higher temperatures correlated with increased respiration rates, peaking at 26 degrees C. In contrast, clearance rates declined beyond 26 degrees C, signifying reduced food intake not mirrored by respiration rates. This response at high temperatures implied a potential negative energy balance, suggesting vulnerability to chronic or repeated thermal stress. Consequently, this study predicted the susceptibility of C. nucula to climate change conditions, with potential repercussions for its metabolic performance, ecological role, and the associated ecosystem services it provides. As a result of climate change, the Mediterranean Sea has been exposed to an increase in the frequency and intensity of marine heat waves in the last decades, some of which caused mass mortality events of benthic invertebrates, including sponges. Sponges are an important component of benthic ecosystems and can be the dominant group in some rocky shallow-water areas in the Mediterranean Sea. In this study, we exposed the common shallow-water Mediterranean sponge Chondrilla nucula (Demospongiae: Chondrillidae) to six different temperatures for 24 h, ranging from temperatures experienced in the field during the year (15, 19, 22, 26, and 28 degrees C) to above normal temperatures (32 degrees C) and metabolic traits (respiration and clearance rate) were measured. Both respiration and clearance rates were affected by temperature. Respiration rates increased at higher temperatures but were similar between the 26 and 32 degrees C treatments. Clearance rates decreased at temperatures >26 degrees C, indicating a drop in food intake that was not reflected by respiration rates. This decline in feeding, while maintaining high respiration rates, may indicate a negative energy balance that could affect this species under chronic or repeated thermal stress exposure. C. nucula will probably be a vulnerable species under climate change conditions, affecting its metabolic performance, ecological functioning and the ecosystem services it provides.
