Invertebrates' metabolic responses to climate warming scenarios in the Adriatic Sea

The unprecedented climate warming is profoundly altering marine life. Metabolic rate, a key organismal trait, serves as an ecological indicator of species' responses to the temperature-driven impacts of climate change, across levels of biological organisation from individuals to ecosystems. Understanding and predicting the temperature responses of metabolic rate is thus urgent for guiding effective policy and conservation efforts, particularly in the semi-enclosed Adriatic Sea, which has recently experienced pronounced changes in invertebrate populations and community composition. Here, we aimed to assess how the standard metabolic rate (SMR) of invertebrate species in the Adriatic Sea responds to temperature changes and to project its change under various IPCC climate emission scenarios by 2100. We measured the individual SMRs of nine invertebrate species collected from locations spanning the southern to northern Adriatic Sea, across two acclimation temperature levels. Relative to theoretical expectations, our findings indicated shallower scaling of SMR with body size (with an overall scaling exponent of 0.50), and lower temperature dependence (with an activation energy of 0.35 eV). We further showed that species in the Adriatic Sea are projected to experience an increase in their metabolic rate ranging from an average 7.8% under the most optimistic Representative Concentration Pathway RCP2.6, to 27.3% under the more severe climate change scenario RCP8.5, with the highest increases expected in the northern area in Gulf of Trieste. Overall, despite lower-than-theoretically expected metabolic temperature dependence in aquatic invertebrates, empirical estimates combined with spatial climate projections indicate that warming will elevate energetic demands throughout the Adriatic Sea, with disproportionately stronger impacts in the northern basin