Copepods are common crustaceans in aquatic systems and one of the most important producers of carotenoidastaxanthin pigments, which can enhance the animals’ resistance against potentially damaging ultraviolet radiation (UVR), but at the same time, increases the risk of fish predation. Previous studies have demonstrated that copepods have different pigmentation levels matching the current threat level in terms of UVR and fish occurrence. However, these other studies have quantified population-levels changes in pigmentation, making it difficult to disentangle the role of individual phenotypic colour changes from that of selection.We quantified carotenoid-based pigmentation with colorimetric methods, which enabled us to track changes within individual copepods. Two species of copepods, Diaptomus castor and Eudiaptomus gracilis, were exposed to high and low UVR and fish cues in a factorial design. L*a*b* colour values (CIE; CommissionInternational de l’Eclairage) were extracted from digital photographs of each copepod and used as proxies for carotenoid concentration. Our results showed that individual copepods significantly changed their pigmentation in response to both UVR and fish cues within a period of 2 weeks. However, the responses differed between sexes and between adults and juveniles. UVR effects were present in all life-stages whereas fish effects were only detected in juveniles, with largest responses in D. castor. This confirms that carotenoid pigmentation is a phenotypically plastic trait, and highlights that strategies for trading off risks of UVR and predation differ between males and females as well as between life-stages.

Many coastal marine systems have extensive areas with anoxic sediments and it is not well known how these conditions affect the benthic-pelagic coupling. Zooplankton lay their eggs in the pelagic zone, and some sink and lie dormant in the sediment, before hatched zooplankton return to the water column. In this study, we investigated how oxygenation of long-term anoxic sediments affects the hatching frequency of dormant zooplankton eggs. Anoxic sediments from the brackish Baltic Sea were sampled and incubated for 26 days with constant aeration whereby, the sediment surface and the overlying water were turned oxic. Newly hatched rotifers and copepod nauplii (juveniles) were observed after 5 and 8 days, respectively. Approximately 1.5 × 10⁵ nauplii per m^-2 emerged from sediment turned oxic compared to 0.02 × 10⁵ m^-2 from controls maintained anoxic. This study demonstrated that re-oxygenation of anoxic sediments activated a large pool of buried zooplankton eggs, strengthening the benthic-pelagic coupling of the system. Modelling of the studied anoxic zone suggested that a substantial part of the pelagic copepod population can derive from hatching of dormant eggs. We suggest that this process should be included in future studies to understand population dynamics and carbon flows in marine pelagic systems.