Jennifer Griffiths joined our group as a postdoctoral fellow. She received a research fellowship from Stockholm University to evaluate the role of multiple pressures on plankton community interactions of the Baltic Sea using novel modeling.
Rossoll, D., Sommer, U. & Winder, M. Community interactions dampen acidification effects in a coastal plankton system. Mar Ecol Prog Ser 486, 37–46 (2013).
Changing seawater chemistry towards reduced pH as a result of increasing atmospheric carbon dioxide (CO2) is affecting oceanic organisms, particularly calcifying species. Responses of non-calcifying consumers are highly variable and mainly mediated through indirect ocean acidification (OA) effects induced by changing the biochemical content of their prey, as shown within single species and simple two-trophic interactions. However, it can be expected that indirect CO2 impacts observed at the single species level are compensated at the ecosystem level by species richness and complex trophic interactions. A dampening of CO2-effects can be further expected for coastal communities adapted to strong natural fluctuations in pCO2, typical for productive coastal habitats.
Here we show that a plankton community of the Kiel Fjord was tolerant to pCO2 levels projected by the end of this century (<1400 µatm), and only subtle differences were observed at extreme high values of 4000 µatm. We found similar phyto- and microzooplankton biomass and copepod abundance and egg production across all CO2 treatment levels. Stoichiometric phytoplankton food quality was minimal different at the highest pCO2 treatment, which was however far from being potentially limiting for copepods. These results contrast studies including single species that observed strong indirect CO2 effects for herbivores, suggesting limitations of biological responses at the organism to the community level. Although this coastal plankton community was highly tolerant to high fluctuations in pCO2, increase in hypoxia and CO2 uptake by the ocean can aggravate acidification and may lead to pH changes outside the experienced range for coastal organisms.
Andrea Downing joined our group as a postdoctoral researcher.
New paper on ocean acidification: Ocean Acidification-Induced Food Quality Deterioration Constrains Trophic Transfer by Rossoll et al., PLoS One.
OA is expected to have far-reaching consequences for marine communities and ecosystems. To date, however, our understanding of the possible impacts of OA is based almost exclusively on single species responses. Here we investigate whether OA can affect trophic interactions by changing the nutritional quality of primary producers and how that translates to higher trophic levels. Our results show that OA can indirectly affect zooplankton growth through its impact on the nutritional quality of phytoplankton, their major food source. We found that the amount of total fatty acids (FAs) and FAs essential for copepod growth and reproduction declined in the food source at increasing levels of OA. Because copepods must obtain these macromolecules from their diet, the shift in algal FA directly transferred to copepods and caused a significant decrease in copepod egg production.
The classic diatom-copepod-fish link in the ocean supports some of the most productive ecosystems in the world and is an important source of highly nutritious food for fish and humans. While previous experiments showed no direct effect of elevated CO2 on copepod growth and reproduction when fed with unmanipulated CO2 diet, our study demonstrates that OA can have far-reaching consequences for ocean food webs by changing the nutritional quality of essential macromolecules in primary producers, cascading up the food web.