Pulsed settlement in an Atlantic cod (Gadus morhua) population drives metabolic plasticity and climate resiliency amid intensifying ocean temperature fluctuations

Climate change is altering ocean temperatures. In the Northwest Atlantic, seasonal cooling (16ºC to -1.5ºC) is expected to drive cold adaptation through genetic or behavioral mechanisms. In fractional spawners, seasonal temperature shifts may cause phenotypic metabolic divergence between settlement pulses within a population, affecting year-class recruitment. We used a retrospective otolith-based stable isotope method to examine relationships between field metabolic rate and temperature in two genetically homogenous age-0 Atlantic cod (Gadus morhua) settlement groups from Newman Sound, Newfoundland. We found significant variation in temperature-corrected field metabolic rates between settlement groups within Newman Sound (metabolic plasticity), and also between Newman Sound individuals and those from a population from the northeast Atlantic (genetic variation). Individuals experiencing higher temperatures during early-development maintain a higher mass and temperature-corrected field metabolic rate than those experiencing cooler ocean temperatures. We conclude that age-0 Atlantic cod in Newman Sound exhibit metabolic plasticity, which could enhance resilience to increasing climate variability imposed by cooling winters in the Northwest Atlantic.