| Summary: | The zooplankton Calanus finmarchicus is a key species in the North Atlantic, by linking the primary production with upper trophic levels and by contributing to vertical export of carbon. Copepod eggs were cultured to a sub-adult stage, under different regimes of temperatures (11 and 14 °C) and pCO2 concentrations (390 and 2080 ppm) in a full factorial design. Morphological characters were measured and the proteome was analyzed using two-dimensional electrophoresis (2-DE) followed by mass spectrometry. To the author s knowledge, this is the first study to use a 2-DE proteomic approach to examine the combined effect of acidification and warming on any marine organism. Somatic growth (body and lipid sac) was reduced in response to warming, but the effects was somewhat ameliorated by acidification in the animals exposed to both stressors. This has not been reported elsewhere, and emphasizes the challenges with predicting the combined effect of acidification and warming. Fourteen proteins were differentially expressed, whereby warming inflicted a more pronounced effect than acidification also on this level. Only a few proteins were affected by acidification alone, and these showed no difference in expression when the copepods were exposed to both stressors. This imply that the acidified effect was ameliorated by warming, which is opposite from what was found for the antagonistic effect observed with the morphological variables. The identified proteins belongs to the cytoskeleton, metabolism or the stress class. The moderate proteome response and the types of proteins affected reflects the changes seen in somatic growth, e.g. an up-regulation of a glycolytic enzyme points to increased metabolism and less energy to store as lipids. Future proteome studies incorporating posttranslational modifications, protein-protein interactions and multiple generations of an organism, may contribute to further knowledge about the mechanisms that are affected by ocean acidification and warming.
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