Temperature-dependent responses in metabolism of Octopus tetricus embryos

Temperature is a primary driver of embryonic development and metabolic demand in cephalopods, yet detailed assessments of how developmental stage and temperature interact to shape metabolic requirements remain limited. This study examined temperature-dependent variation in standard metabolic rate (SMR) and routine metabolic rate (RMR) of Octopus tetricus embryos using closed-system respirometry. Embryos were measured at five Naef developmental stages (IV, VIII, XII, XVI, and XX) across six temperatures (12-27 °C), spanning and exceeding the species' natural thermal range. Both SMR and RMR were significantly influenced by the interaction between temperature and developmental stage, exhibiting pronounced non-linear patterns throughout embryogenesis. Metabolic demand generally increased with ontogenetic development, with the largest increases occurring in late-stage embryos prior to hatching. Early-stage embryos displayed relatively low and stable metabolic rates among temperatures, whereas late-stage embryos showed sharp increases with increasing temperature. Thermal sensitivity of metabolism intensified with development, with highly variable and extreme Q₁₀ values observed in later stages, indicating heightened susceptibility to temperature fluctuations near hatching. Notably, metabolic responses did not conform to uniform thermal scaling relationships over the developmental stages. Comparisons with other cephalopod species suggest that while absolute metabolic rates in O. tetricus are moderate, late-stage embryos exhibit comparatively high thermal sensitivity. These findings demonstrate that developmental stage is a primary determinant of embryonic metabolic performance, with late embryogenesis representing a critical window of heightened energetic demand and physiological vulnerability. This work provides new insight into the role of temperature in shaping embryonic performance and offers a physiological basis for improving incubation practices and predicting early life-stage responses to ocean warming.