Contrasting metabolic responses to increasing temperature in four mediterranean echinoderms

Abstract

<p>Marine ectotherms, organisms whose body temperature depends on their environment, often rely on physiological plasticity</p><p>to withstand rapid temperature increases when behavioural adjustments are insufficient. Despite extensive research</p><p>on thermal tolerance, gaps remain in understanding species- and population-level metabolic responses to acute thermal</p><p>stress, particularly in rapidly warming regions like the Mediterranean Sea. This study assessed metabolic responses to</p><p>acute warming in four echinoderm species with distinct thermal affinities but overlapping distributions in the Western</p><p>Mediterranean: the sea urchins Arbacia lixula (subtropical) and Paracentrotus lividus (temperate-cold), and the brittle</p><p>stars Ophiothrix sp. II (temperate) and Ophiocomina nigra (temperate-cold). Oxygen consumption, used as a proxy for</p><p>Basal Metabolic Rate (BMR), was measured at sequential temperatures (16 °C, 20 °C, 23 °C, 26 °C), following a short</p><p>acclimation period. Species exhibited divergent metabolic trajectories and thermal sensitivities (Q₁₀), reflecting their thermal</p><p>affinities, local adaptations, and phenotypic plasticity. A. lixula and Ophiothrix sp. II displayed sharp BMR increases,</p><p>indicating resilience but proximity to their upper thermal limits. In contrast, O. nigra maintained stable metabolic rates,</p><p>suggesting broad physiological plasticity. P. lividus displayed population-level divergence: individuals with cooler-origin</p><p>experienced metabolic suppression and severe thermal stress at 26 °C, whereas those with warmer-origin maintained</p><p>higher metabolic activity. Overall, phenotypic plasticity emerged as a key short-term strategy to cope with acute warming.</p><p>However, species with narrower thermal tolerance, such as P. lividus, might face long-term vulnerability under intensifying</p><p>marine heatwaves. These results highlight the importance of integrating thermal history, plasticity, and genetic variation</p><p>to accurately predict resilience to ocean warming.</p>