Working Group Food Web
The Food Web Group focusses on complex interactions between planktonic organisms concentrating on primary producers at the base of the food web (phytoplankton) and their primary and secondary consumers (e.g. micro- and mesozooplankton). Planktonic food webs are considered as highly complex with a plethora of different feeding interactions, spatio-temporal dynamics and functions in the plankton. The characterization of Shelf Sea food webs is our central aim. By using field and experimental approaches, we address the effects of external (e.g. nutrients, temperature, light, hydrodynamics, CO2, O2) and internal drivers (intra- and inter-specific interactions) on food web structure and dynamics as well as bottom-up and top-down control mechanisms that either limit organisms by resource availability or include predation and herbivory at each trophic level.
Micrograzers play a prominent role as trophic link between microbial and classical food webs. As a result, we specifically consider small-sized protozoa (e.g. heterotrophic dinoflagellates, ciliates) and metazoa (e.g. meroplanktonic larvae, nauplii) in the plankton. Especially the ability of micrograzers to (1) buffer nutritional imbalances at the base of the food web, (2) suppress and modulate phytoplankton blooms and (3) improve the food quality for secondary consumers are central aspects of our research. By using multi-trophic approaches, we further aim to assess the impact of food quantity and quality aspects on the transfer of limitation signals and on energy transfer efficiencies onto higher trophic levels.
As a result from increases in atmospheric pCO2, seawater pH is predicted to drop. This effect is referred to as ‘ocean acidification (OA)’ and it is considered that increases in pH will negatively affect marine ecosystems. While there is some knowledge on specific effects of OA on the physiology and biochemistry of individual marine taxa, many uncertainties remain on how these responses translate up the food web. By simulating different pCO2 conditions, the ‘Food Web’ group experimentally analyses the effects of OA on plankton communities in cooperation with national and international partners (e.g. within the framework of BIOACID) in order to assess the vulnerability and potential consequences for all trophic components in the plankton. Apart from direct pH sensitivities of specific groups and species, indirect effect of OA resulting from e.g. changes in phytoplankton community structure, size classes, biomass and/or stoichiometry of microzooplankton as well as larger zooplankton (e.g. copepods), fish and jelly fish are analysed.