Plankton and its traits

Increase in global oceanic NPP by >2 Pg-C yr-1 from 1985 to 2085 due to PVM
(Wirtz et al Nature Climate Change 2022)

The name plankton can be misleading because a majority of planktonic organisms are not just dumb drifters but regulate their vertical position in the water column and can thus access very different habitats. Our group has recently discovered -by modeling and compilation of indirect evidence- that bulk phytoplankton in the world oceans exhibits a migratory behavior. In the deep, phytoplankton cells take up nutrients, which are scarce in upper water layers. After ascending, these microscopic commuters fuel their carbon store by photosynthesis and then descend again to deeper waters. This migratory behavior has significant effects on the global carbon cycle.

Phytoplankton Vertical Migration

Phytoplankton Vertical Migration (PVM) as an adaptive behavior for resource acquisition in the widespread case of depleted nutrients at the surface. By descending to the chemocline at higher depth, autotrophic cells accumulate internal nutrient stores, while they gain energy and carbon after ascending to the sunlight upper ocean.

CHL

1D Lagrangian model for the emergence of the subsurface chlorophyll (CHL) maximum due to PVM.

Our group develops innovative mechanistic trait-based models to describe the response of plankton and other ecosystem departments to multiple external drivers including Climate Change. We are also advancing the modular coupling of trait-based ecosystem models to physical models MOSSCO in order to describe the interaction between ocean physics and biological processes most efficiently. In many of our studies and projects (MuSSeL, ) we investigate the long-term ecosystem dynamics for identifying key drivers but also for evaluating mitigation strategies.
Using the first coupled, adaptive trait-based ecosystem model, the Model for Adaptive Ecosystems in Coastal Seas (MAECS), we could reconstruct long-term changes in ecosystem functioning but also plankton ecophysiology in the Southern North Sea (Wirtz 2019, data-set, Xu et al). For example, we revealed a critical importance of viral dynamics for the break-down of the phytoplankton spring bloom (Wirtz 2019, Krishna et al 2023), or the relevance of light conditions for a strong top-down regulation of coastal ecosystems.
Our numerical experiments always rely on extensive data integration and analysis and unravel how bottom-up and top-down controls are mediated by adaptive processes (trait variations) and system feed-backs.