Temperature-induced metabolic performance in early life stages of two brachyuran crabs

Understanding marine species' metabolic responses to short- and long-term temperature variation is critical for predicting the resilience of communities and ecosystems at local and global scales. This study investigated the effect of temperature on the routine metabolic rate (RMR) across the zoea and megalopa stages of two brachyuran species, Hymenosoma orbiculare and Pinnotheres sp. Respirometry results under temperatures ranging from 11 to 25 °C revealed stage- and species-specific metabolic responses. In H. orbiculare, RMR in the megalopa life stage increased steeply and significantly at 22 °C, whereas the zoea life stage showed no significant change across the temperature range tested. For Pinnotheres sp., the megalopa life stage also exhibited significant RMR increases above 19 °C, while the zoea life stage showed stable RMR. These results demonstrate that megalopae, particularly H. orbiculare, are more metabolically sensitive to acute warming, operating closer to their physiological limits, while zoeae maintain relative stability, but may be constrained by limited plasticity under sustained warming. Species-level comparisons indicate that H. orbiculare, with its higher and more variable RMR, is more vulnerable than Pinnotheres sp., whose larval stages maintain comparatively stable metabolism. This study highlights the importance of understanding life-stage- and species-specific thermal responses to better predict larval survival, recruitment, and resilience under future climate warming.