Pelagic food webs
The group focuses on trophodynamic interactions within pelagic food webs ranging from:
- Primary producers at the base of the food web (phytoplankton)
- Secondary consumers (micro- and mesozooplankton e.g. heterotroph protists, gelatinous zooplankton, meroplankton)
- Tertiary consumers (meso-, macro- and megazooplankton e.g. ichthyoplankton, gelatinous zooplankton, meroplankton)
External and internal drivers
Pelagic food webs are considered as highly complex with a variety of feeding interactions, spatio-temporal dynamics and functional traits. We use field and experimental approaches to assess the role of:
- External drivers (e.g. nutrients, temperature, light, hydrography) on trophodynamic interactions, functional traits and diversity
- Internal drivers (intra- and inter-specific interactions) on shaping pelagic community structure and food web interactions.
The role of micrograzers (20-200 µm) as a trophic link between microbial and classical food webs are a special focus area. We analyse communities of small-sized protozoa (e.g. heterotrophic dinoflagellates, ciliates) and metazoa (e.g. meroplanktonic larvae, nauplii) focussing on 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. Here, multi-trophic approaches are used to analyse food quantity and quality aspects within planktonic food-webs and interactions between micrograzers and larger zooplankton e.g. early life stages of fish larvae. The functioning of micrograzers with regard to trophic transfer efficiencies and alterations in energy transfer to higher trophic levels are considered in detail.
Core topics of current and future research activities
- Climate change impacts (global warming, ocean acidification) on pelagic communities in low and high latitude regions
- Impact of external stressors (e.g. changes in temperature, pH, salinity, light or nutrients) on match-mismatch situations in the plankton
- Alterations in microplankton community structure and potential consequences for trophic transfer efficiencies up the food web
- Bloom formation and phenology patterns of key zooplankton groups (microzooplankton, ichthyoplankton, jellyfish)
The methodological approaches range from field observations to small- or large-scale experimental approaches using e.g. mesocosm set-ups in order to simulate future ocean conditions (warming, oacean acidification). The aim is to create near-natural conditions by using e.g. natural plankton communities and applying different stressors to the system (e.g. changes in temperature, pH, salinity, light or nutrients).