Work Package 3
Pelagic food-web structure, trophic interactions and the role of zooplankton for overall trophic transfer efficiency in the Humboldt Current upwelling system off Peru
Work Package Leaders
- Prof. Dr. Wilhelm Hagen (University Bremen) - whagen (at) uni-bremen.de
- PD Dr. Holger Auel (University Bremen) - hauel (at) uni-bremen.de
- Dr. Rolf Koppelmann (University Hamburg) - rolf.koppelmann (at) uni-hamburg.de
- Dr. Silke Lischka (Univesity Kiel) - slischka (at) geomar.de
- Dr. Jens C. Neijstgaad (IGB) - nejstgaard (at) igb-berlin.de
- Dr. Stella A. Berger (IGB) - berger (at) igb-berlin.de
All four major EBUS support similar rates of primary production (~900 g C m-2 a-1), but the Humboldt Upwelling System (HUS) is by far the most productive system with regard to fisheries, yielding on average eight times more fish than the other three EBUS. Such an enormous productivity at upper trophic levels despite similar primary production rates can only be explained by higher trophic transfer efficiencies (TTE). To elucidate the reasons for the high TTE in the HUS, WP3 will analyse the plankton food web structure and quantify major trophic pathways with special focus on microzooplankton and dominant mesozooplankton taxa. These investigations will be conducted during an oceanographic cruise with RV M.S. Merian in 2019 and a mesocosm experiment off Callao in 2020, in close collaboration with partners at the Instituto del Mar de Peru (IMARPE) in Lima.
- The length of the planktonic food chain between primary producers and harvested species will be assessed via trophic markers (e.g. stable isotopes, fatty acids) to help resolve TTE
- The role of larger filter feeders (e.g. euphausiids) in the HUS will be examined via field data on community composition, since krill species efficiently consume a wide range of prey sizes forming less complex food webs with a higher overall TTE
- The abundance and trophic position of gelatinous and semi-gelatinous zooplankton will be examined, since these are often "dead ends" of the food chain and exhibit prey competition with small pelagic fish
- The role of microzooplankton and the influence of the microbial loop will be investigated in mesocosm experiments, simulating different intensities of upwelling to quantify the effects on the TTE
- Feeding and egg production rates of dominant copepods will be measured under different simulated upwelling intensities in mesocosms as a measure of TTE
Based on these activities the aim is to:
- assess the effect of physical-biological boundaries (meso-scale eddies and filaments or the intense OMZ) on the zooplankton dynamics of the HUS, since prey and predators often aggregate at these water mass boundaries and less energy is required for the search of food, which is expected to result in a higher overall TTE.
- develop food web models in cooperation with WP2, 4 & 6.
KOSMOS experiment, Peru 2017 (Photo: Silke Lischka)
Multinet Midi, equipped with five nets for stratified mesozooplankton collections (Photo: Dominik Auch)
Sunset sampling, with multinet on working deck (Photo: Dominik Auch)
Collection dominated by gelatinous zooplankton (Photo: Dominik Auch)
Various decapod shrimps from the deep sea (Photo: Holger Auel)
Red squat lobster (Pleuroncodes monodon), a highly abundant species in the HUS (Photo: Holger Auel)