Modelling Seasonal Vertical Migration in Marine Zooplankton

• Applicant: Dr. Markus Pahlow
• Subject Area: Oceanography ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 394725389

Seasonal vertical migration (SVM) of marine mesozooplankton potentially plays a key role in determining primary and export production in higher latitudes with pronounced seasonality. SVM is an important part of the behaviour of many marine mesozooplankton communities at high latitudes, enabling these organisms to exploit the biomass produced during spring blooms efficiently. The timing of the SVM ascent in early spring and descent in summer are essential for maximising food availability and minimising the risk of predation by larger animals: ascending too early or too late can result in starvation and descending too late can increase the likelihood of being eaten (match-mismatch hypothesis). SVM is less important or absent in low-latitude ocean regions with little seasonality. Owing to these complications, most biogeochemical models define zooplankton behaviour only through their feeding, and ignore any migratory behaviour.SVM has been considered in individual-based models (IBMs) geared towards the seasonal development and regional distribution of copepods and their life stages in several ocean regions. However, IBMs are computationally too expensive for applications in 3D global models, particularly for simulations over long time scales. In previous biogeochemical modelling projects, we have found significant mismatches between observed and predicted secondary production in high-latitude locations, likely related to the lack of SVM behaviour in the model. We propose to develop simpler, trait- and optimality-based models amenable for representing SVM in large-scale models capable of long-term simulations on time scales of decades to centuries. We will use modelling techniques we have developed previously to explore how traits, such as the day of ascent, or degree-days, control SVM behaviour and its evolution.We will develop trait-based descriptions of SVM for analysing the driving forces of SVM behaviour, first in 1D and then also in 3D biogeochemical models. The main goal of this project is thereby an understanding of which environmental factors determine the evolution of SVM behaviour locally and how they shape global patterns in SVM behaviour and its effects on plankton ecology and biogeochemistry. We will then analyse the potential of including SVM behaviour in global models for improving their overall ability to describe observed biogeochemical fields, e.g., distributions of nutrient concentrations and primary and export production. Finally, we will evaluate the effect of considering SVM behaviour on long-term simulations of past and future climate scenarios.Our project entails strong links between DynaTrait and other large research projects, benefitting from and contributing to the DFG-funded SFB 754 on oxygen minimum zones and the BMBF-funded PalMod project on long-term climate simulations. Thus, our work will significantly improve the visibility and relevance of trait-based modelling in the global-modelling community.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1704: Flexibility Matters: Interplay Between Trait Diversity and Ecological Dynamics Using Aquatic Communities as Model Systems (DynaTrait)
• International Connection: Japan
• Co-Investigator: Dr. S. Lan Smith