Final Activity Report Summary - CARBON TRANSFER (Trophic carbon transfer efficiency under carbon dioxide stress)
Carbon dioxide (CO2) is taken up from the atmosphere into the oceans in proportion of its concentration and, in its dissolved form, increases the acidity of the ocean, resulting in lower pH. Recent evidence suggests that increasing dissolved CO2 concentrations in the ocean and the associated decrease in pH affect cell physiology, biochemical and elemental composition and community structure of phytoplankton. Apart from the seasonal varying food availability in the ocean, the biochemical composition of the phytoplankton is a key factor controlling both growth and reproduction of herbivorous zooplankton and, therefore, the efficiency at which the phytoplankton is transferred into secondary production.
Laboratory experiments were conducted to test whether the growth or reproduction of two common marine copepod species, namely temora longicornis and acartia tonsa, was altered by potential changes in the quality of their food associated with ocean acidification. For these tests, three typical phytoplankton species representing the major food that was encountered by the copepods during the seasons, i.e. the diatom thalassiosira weissflogii, the dinoflagellate prorocentrum minimum and the nuisance bloom-forming flagellate phaeocystis globosa, were chosen and grown in continuous culture under either present day atmospheric conditions or at enhanced CO2 concentrations representing the expected conditions for the years 2050 and 2100.
In agreement with other recent investigations, no direct anaesthetic or lethal effect on the copepods was observed. For the first time, however, it could be shown that copepods could be indirectly affected by changes in food quality. The effect depended strongly on the food species in question, but was in general reflected in a change of egg production. While the quality of the diatom for copepod reproduction showed only small changes with increasing acidification, the egg production of copepods increased strongly with the two other algae indicating that their quality considerably improved. In case of the dinoflagellate, it could be shown that feeding changed little with changing pH, indicating that the biochemical quality was likely improved. In contrast, the response in copepod reproduction to phaeocystis was mainly explained by a relaxation of the feeding deterrence activity of this nuisance species. Altogether, the results emphasised that food web interactions and the carbon transfer efficiency could considerably change under future climate changes, however these changes would not necessarily be negative.
Laboratory experiments were conducted to test whether the growth or reproduction of two common marine copepod species, namely temora longicornis and acartia tonsa, was altered by potential changes in the quality of their food associated with ocean acidification. For these tests, three typical phytoplankton species representing the major food that was encountered by the copepods during the seasons, i.e. the diatom thalassiosira weissflogii, the dinoflagellate prorocentrum minimum and the nuisance bloom-forming flagellate phaeocystis globosa, were chosen and grown in continuous culture under either present day atmospheric conditions or at enhanced CO2 concentrations representing the expected conditions for the years 2050 and 2100.
In agreement with other recent investigations, no direct anaesthetic or lethal effect on the copepods was observed. For the first time, however, it could be shown that copepods could be indirectly affected by changes in food quality. The effect depended strongly on the food species in question, but was in general reflected in a change of egg production. While the quality of the diatom for copepod reproduction showed only small changes with increasing acidification, the egg production of copepods increased strongly with the two other algae indicating that their quality considerably improved. In case of the dinoflagellate, it could be shown that feeding changed little with changing pH, indicating that the biochemical quality was likely improved. In contrast, the response in copepod reproduction to phaeocystis was mainly explained by a relaxation of the feeding deterrence activity of this nuisance species. Altogether, the results emphasised that food web interactions and the carbon transfer efficiency could considerably change under future climate changes, however these changes would not necessarily be negative.