| Summary: | The manuscripts of the dissertation presented here encompass several aspects of adaptations in ice-associated amphipods, focussing mainly on their ability to cope with increased light levels, including the ultraviolet radiation (UVR), under thinner or more dispersed sea ice. A decrease in multi-year ice (MYI) in the Arctic, and a concurrent reduction in stable habitat for ice-associated species, is a substantial threat to the ecosystem in the Arctic Ocean, as these amphipods act as a key trophic link between primary production inside and under sea ice, and higher trophic levels. In a shift from thicker multi-year ice to thinner and less coherent first-year ice, the changes in under-ice light levels may be considered as the second-most significant factor, after the loss of the habitat itself. This thesis has as its overarching ambition to contribute to our understanding of how this change may affect the organisms living in association with the Arctic sea ice. While the reduction in stratospheric ozone and the resulting seasonal increases in ultraviolet radiation (UVR) have been halted and to some extent reversed, the recovery period is calculated to be protracted, and might even be affected negatively by the ongoing warming of the troposphere through the ongoing emission of greenhouse gases. So both the direct and indirect effects of UVR on sea ice-associated amphipods have been proven to be a significant factor, especially in the context of a reduction in both thickness and extent of the Arctic sea ice cover. The effects of pigment ingestion and accumulation have also been of particular interest, as well as the capacity of organisms to cope with and adapt to elevated, radiation-induced oxidative stress. Another aspect of this thesis has been to investigate hitherto and potentially overlooked aspects of the distribution and occurrence of ice-associated amphipods in the Antarctic. This study contributed to altering the previously held assumption that ice-associated amphipods in Antarctic waters were predominantly ...
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