Physiological resilience of intertidal chitons in a persistent upwelling coastal region

Current climate projections for mid-latitude regions globally indicate an intensification of wind-driven coastal upwelling due to warming conditions. The dynamics of mid-latitude coastal upwelling are marked by environmental variability across temporal scales, which affect key physiological processes in marine calcifying organisms and can impact their large-scale distribution patterns. In this context, marine invertebrates often exhibit phenotypic plasticity, enabling them to adapt to environmental change. In this study, we examined the physiological performance (i.e., metabolism, Thermal Performance Curves, and biomass and calcification rates) of individuals of the intertidal mollusk Chiton granosus, a chiton found from northern Peru to Cape Horn (5° to 55°S). Our spatial study design indicated a pattern of contrasting conditions among locations. The Talcaruca site, characterized by persistent upwelling and serving as a biogeographic break, exhibited lower pH and carbonate saturation states, along with higher pCO₂, compared to the sites located to the north and south of this location (Huasco and Los Molles, respectively). In agreement with the spatial pattern in carbonate system parameters, long-term temperature records showed lower temperatures that changed faster over synoptic scales (1-15 days) at Talcaruca, in contrast to the more stable conditions at the sites outside the break. Physiological performance traits from individuals from the Talcaruca population exhibited higher values and more significant variability, along with significantly broader and greater warming tolerance than chitons from the Huasco and Los Molles populations. Moreover, marked changes in local abundance patterns over three years suggested population-level responses to the challenging environmental conditions at the biogeographic break. Thus, C. granosus from the Talcaruca upwelling zone represents a local population with wide tolerance ranges that may be capable of withstanding future upwelling intensification on the Southern Eastern Pacific coast and likely serving as a source of propagules for less adapted populations.