Increasing human activities and CO2 release to the atmosphere cause global ocean warming and acidification, as well as local oxygen depletion and eutrophication. Laboratory experiments on single species and single stressors show variable responses within and between species and different combinations of stressors can have synergistic, additive or antagonistic effects. Thus, only large-scale multi-species and multi-stressor experiments can predict future community responses. For this purpose, a new benthic mesocosm facility was build at the AWI Wadden Sea Station - Sylt. Each of 12 1,800 l benthocosms serves as independent experimental unit with current and tide simulations as well as multi-parameter control systems to simulate multi-factorial future climate change scenarios such as warming, ocean acidification, eutrophication and extreme weather events. Temperature, pH, oxygen, and salinity are monitored continuously and logged separately for each benthocosm. Additional variables such as total alkalinity, light availability, Chl a, nutrients, DOC or POC are monitored manually.
We are investigating the responses of North Sea F. vesiculosus, and its associated community to warming and ocean acidification as well as to the combination of these stressors. Fucus communities were to date incubated in two experimental approaches for 2-3 months under the interactive effects of warming and elevated pCO2 in autumn 2013 and spring 2014. Warming reduced the overall biomass of F. vesiculosus in the system but favoured the reproduction and survival of herbivores (mainly Gammarus sp.). In contrast, elevated pCO2 increased Fucus growth, while the interactive effects of warming and acidification had antagonistic effects leading to no difference compared to the ambient treatment. We furthermore examine physiological responses of F. vesiculosus and its epibionts as well as its consumers. Compared to North Sea ecosystem responses, experiments conducted within the benthocosms facilities at the GEOMAR - Kiel with Baltic Sea communities, show a controversial outcome, where CO2 related impacts on the macrophyte community were much weaker, as were the interactive impacts of warming and elevated pCO2.
This leads to the assumption that ocean acidification seems to have a higher impact on the Wadden Sea ecosystem as can be predicted for Western Baltic Sea communities, which already today experience natural high fluctuating pCO2.
EPIC Alfred Wegener Institut