Predicting the water temperature effects and climate change impacts on gametogenesis of the sea urchin Mesocentrotus...

Ocean warming has caused shifts in the distribution of ectothermic species, including the sea urchin Mesocentrotus nudus, which is commercially harvested in northern Japan. We constructed a developmental index (DVI) model driven by water temperature to simulate the annual reproductive cycle of males and females and the effect of water temperature on reproduction. Within the distribution range of this species, this DVI model successfully simulated the seasonal changes in the gonad developmental stages of M. nudus from Stage 1 (recovering; before gametogenesis) to Stage 5 (spent; after spawning). Simulations with multiple combinations of minimum and maximum temperatures showed that males and/or females could not reach Stage 5 within a calculation period of 365 days when the minimum temperature was <2 °C or >11 °C, regardless of the maximum temperature. Females were more sensitive to temperature change than males. Simulations using 1982-2010 sea surface temperature (SST) around Japan suggested that the northern boundary of distribution may be limited by female gametogenesis failure, and the southern boundary by male gametogenesis failure. Minimum temperatures of 4-8 °C and maximum of 20-22 °C were estimated to be appropriate for successful reproduction. Simulations using 2010-2024 SST showed that the northward shift of the southern limit of distribution observed in the 2010s would have resulted from an increase in the maximum temperature exceeding the thermal tolerance for survival of this species. These findings appear to contribute to explaining the mechanism of climate change impacts on reproduction, harvest season and distribution of M. nudus.