The impact of climate change on the distribution of serpulid polychaetes: an ecophysiological approach

Temperature influences the physiological performance of marine ectotherms-affecting survival, growth, and reproduction-and ultimately shaping their distribution. However, knowledge of how ocean warming will impact sessile ectotherms, such as serpulid polychaetes, remains limited. We hypothesize that rising ocean temperatures will affect serpulid thermal performance, potentially altering their distribution patterns. By combining laboratory-derived ecophysiological data with satellite sea-surface temperature (SST) data, we evaluated the effects of ocean warming on the distribution of two serpulid species from distinct regions: the temperate northern Pacific (Spirobranchus spinosus) and the tropical eastern Pacific (Spirobranchus cf. corniculatus). Adult worms were collected from the wild and acclimated for 30 days at different temperature ranges (11-20 °C for S. spinosus; 24-33 °C for S. cf. corniculatus) to assess thermal tolerance limits (CTmax, CTmin), thermal tolerance window, optimal temperature, and thermal safety margins. These physiological data were integrated with SST data to model potential distributions for both present (2010-2020) and future (2090-2100, SSP5-8.5) climate change scenario. Thermal tolerance limits increased with acclimation temperatures in both species. However, S. cf. corniculatus exhibited similar CTmax (35.1 °C) values at 30 and 33 °C, suggesting it is approaching its upper thermal limits. Both species exhibited narrow thermal windows (S. spinosus: 37 °C²; S. cf. corniculatus: 71 °C²), characteristic of stenothermic species. The optimal temperatures were 14 °C for S. spinosus and 30 °C for S. cf. corniculatus. By century's end, thermal safety margins are predicted to decrease, leading to range retractions in S. spinosus and potential poleward expansions in S. cf. corniculatus. These findings underscore the importance of integrating physiological and environmental data to assess the vulnerability of sessile ectotherms to climate change. Although other factors such as pH, currents, and oxygen may influence future distributions, this study provides an important first step toward understanding climate change impacts on sessile marine ectotherms.