Responses of calanoid and harpacticoid copepods to rising temperatures : a multigenerational perspective

Climate change poses a major global challenge, yet long-term effects on key marine invertebrates remain unclear. This dissertation investigates how rising water temperatures, both gradual and sudden, affect the nutritional value, reproduction, and molecular responses of pelagic and benthic copepods. Experiments on Acartia tonsa showed that gradual warming allows acclimation without major changes in fatty acid profiles, though DNA methylation patterns reveal molecular adjustments. In contrast, sudden heat spikes reduce omega-3 levels and nutritional quality, indicating acute stress. A second experiment on Nitocra spinipes confirmed that gradual warming enables partial multigenerational adaptation, while sudden temperature stress leads to reproductive failure. However, reproductive capacity recovered when normal conditions were restored, highlighting epigenetic resilience. Fatty acid composition was also altered, with decreases in DHA under warming. A dedicated heatwave simulation showed species-specific responses, with N. spinipes potentially relying more on epigenetic mechanisms than A. tonsa, though high mortality limited certainty. Overall, gradual warming promotes acclimation through reversible epigenetic changes, while sudden heat events pose immediate risks to copepod health and food web stability. Understanding transgenerational plasticity and epigenetic stress markers is crucial for predicting ecosystem responses under future climate scenarios.