UVR requires different types of responses because it acts both on long and on short-term scales. The wavelengths of UVR that currently reach the Earth��s surface, independent of any ozone depletion events, cause severe Sarafloxacin HCl cellular damage, most notably, DNA damage. The link between sunlight and potential damage is well established for a variety of aquatic organisms. Early studies have indicated that the mechanisms of damage and the processes of repair at the cellular level are similar for prokaryotes and eukaryotes. Zooplankton must integrate environmental information and use a variety of mitigating strategies to counteract the damaging effects of UVR. Such responses include photoprotective compounds, behavioural responses, and photoenzymatic repair. At the organism level, a response depends on and must be integrated with cell-level signals and conditions, such as oxidative stress damage, antioxidant defence concentrations, and enzymatic expression that are likely to be governed by a succession of changes at the molecular level acting at the time scale of hours. This hierarchical integration can extend further ecological fitness indicators, such as reproduction, survival, and responses to predation risk. For example, cell division, apoptosis, and growth factors must be precisely coordinated in order to guarantee the organism��s success, which demonstrates the need for balance and harmonization between such conditions and effects. Zooplankton may conform to long-term shifts in UVR intensity by adjusting their levels of photoprotective compounds, accomplishing this in days to weeks. Shorterterm shifts such as daily cycling of UVR can be handled with behaviour like vertical migration. Further, in order to meet and counter the detrimental effects of rapid and strong fluctuations in UVR within a day, organisms may also take advantage of enzymatic responses at the cellular level. In a pioneering work, Borgeraas and Hessen reported on diel variations in activity of the antioxidant enzymes in arctic Daphnia. Glutathione S-transferase is a detoxifying enzyme involved in the removal of reactive organic hydroperoxides. For zooplankton it represents a key enzymatic defence against reactive oxygen species that are produced by UVR. In addition to its role in causing oxidative stress, UVR was recently characterized as one of the most important pro-apoptotic stimuli for Cefoperazone crustaceans. Apoptosis may play, in pluricellular organisms, an important role during developmental stages as embryogenesis and metamorphosis. More specifically, during development many cells are produced in excess and eventually undergo programmed cell death, but in the interim they contribute to the ��sculpturing’of organs and tissues. However, apoptosis will also play a protective role when eliminating damaged and unrecovered cells. Among zooplankton, copepods are characterized by a complex development with different stages including nauplii and juveniles.