Hildebrandt, N. (2014). The response of three dominant Arctic copepod species to elevated CO2 concentrations and water temperatures. Ph.D. Dissertation, Universität Bremen, Bremerhaven, Germany. 173 pp.
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Hildebrandt, N.
2014
The response of three dominant Arctic copepod species to elevated CO2 concentrations and water temperatures.
Ocean acidification (OA), i.e. the uptake of man-made CO 2 and the subsequent decline in seawater pH, and ocean warming have the potential to severely affect the performance of marine organisms, their trophic interactions and, finally, whole ecosystems. In Arctic waters, the calanoid copepod species Calanus finmarchicus, C. glacialis and C. hyperboreus are key components of the lipid-based food web, linking primary production and higher trophic levels. Within the framework of the research project BIOACID (Biological Impacts of Ocean Acidification), this study aims to provide a comprehensive overview on the sensitivity of the three Calanus species to ocean acidification and ocean warming. In controlled laboratory CO 2 incubation experiments, direct physiological and ecological effects of elevated pCO 2 were investigated in both active and diapausing Calanus life stages, and synergistic effects of pCO 2 and temperature were studied. In addition, indirect effects of OA via altered food regimes were tackled in an ecosystem-scale experiment within the framework of the SOPRAN (Surface Ocean Processes in the Anthropocene) mesocosm study in 2011.
Late copepodites and adult females of C. finmarchicus, C. glacialis and C. hyperboreus have been proven to be rather robust to elevated seawater pCO 2 in terms of direct effects. In active life stages, metabolic rates and thus the energetic demand were unaffected by CO 2 concentrations of up to 3000 µatm (pH 7.2), which is well beyond the levels projected to occur in surface waters during the next three centuries. Accordingly, food uptake and body mass were not altered, suggesting that also the available energy for processes such as reproduction and growth will not directly be affected by OA in future decades.
During their resting phase in deep waters in fall/winter, copepods might be especially threatened by climate change induced stress as they are not able to compensate for elevated energetic needs. However, our long-term incubation experiments over 17 weeks did not indicate that elevated pCO 2 affects diapausing Calanus, as neither respiration rates, body mass, gonad development nor the acid-base status in the hemolymph were altered in C. hyperboreus females, which were incubated at high CO2 conditions compared to the control. The extracellular pH was found to be extremely low (< 6.6) in diapausing Calanus. This suggests that diapausing copepods may not be challenged by the threats of elevated seawater pCO 2 due to their ability of regulating their acid-base status.
Significant effects were, however, found when copepods were exposed to elevated pCO 2 in combination with higher seawater temperatures. At 3000 µatm CO 2 and 5 °C, C. hyperboreus females lost significantly more body mass as compared to copepods kept at control conditions, indicating that they suffered from elevated energetic demands. However, respiration, gonad maturation, extracellular pH and survival were not affected.
Elevated temperatures (5 and 10 °C) in general had greater effects on the copepods than CO2 , altering respiration, gonad development and probably decreasing the total reproductive output. However, a climate change-induced temperature increase of up to 10 °C will unlikely occur in nature, and it remains open whether more realistic temperature changes will still affect the performance of diapausing Calanus species.
Indirect effects of OA via altered food regimes might be a more serious threat to the Arctic Calanus species as compared to direct effects. During the mesocosm study, indications were found that the copepod’s body mass might be negatively affected in high pCO 2 environments. OA has the potential to alter the size regime of the phytoplankton community, favoring the growth of picoplankton. As the Arctic Calanus species are not able to successfully graze on these small organisms, they might become severely affected in future decades. Thus, future studies should more extensively focus on the indirect effects of OA on Calanus species and the copepod community in general, also in combination with elevated temperatures.
