Multigenerational exposure reveals differential effects of ocean warming temporal scenarios on mercury toxicity in a marine copepod

Marine biota have been facing co-occurring stressors of ocean warming and mercury pollution for generations. However, whether and how different temporal scenarios of warming will affect mercury toxicity in organisms remain poorly understood. Here, we conducted a multigenerational experiment (F1−F5) to investigate the effects of three warming scenarios (developmental, stepwise, and future) on mercury toxicity (1 μg/L) in the marine copepod Pseudodiaptomus annandalei. The results showed that all three warming scenarios increased mercury accumulation in mercury-treated copepods, thereby exacerbating mercury toxicity, with the most severe toxicity response under future warming. Our phenotypic trait analysis showed that the three warming scenarios significantly decreased fecundity and grazing rate, while shortening the development time of mercury-treated P. annandalei compared to ambient temperature condition, ultimately compromising its population fitness. We further integrated transcriptomic and proteomic analyses for the copepods of F5. The findings indicated that the three warming scenarios decreased energy production and impaired detoxification defense, with the most pronounced molecular response occurring under future warming, providing a mechanistic understanding about increased mercury toxicity under different warming scenarios. Overall, our finding highlights the significant risk of different warming scenarios on mercury toxicity in marine copepods and provides a comprehensive understanding of multistress interaction, i.e., climate change and metal pollution, under realistic, temporally dynamic scenarios.