Transient Dynamics in the Vertical Competition Between Sinking and Buoyancy-Regulating Phytoplankton Species

In the temperate zone of the Northern Hemisphere, lakes typically exhibit seasonal patterns of thermally stratified and fully mixed periods. Global warming is altering these cycles, particularly by prolonging summer stratification. Phytoplankton dynamics are closely linked to these patterns: spring bloom formation is typically associated with higher average light availability with the onset of summer stratification, yet stratification also increases the risk of cells sinking out of the euphotic layer. To avoid sinking, many phytoplankton species have evolved motility traits such as flagella or buoyancy regulation. Observations from deep, clear-water lakes in the Northern Hemisphere suggest that especially low-light-adapted cyanobacteria, such as Planktothrix rubescens, might benefit from extended stratification periods through their capacity to vertically migrate via active buoyancy regulation. This trait may confer a competitive advantage over sinking species. Using a 1D model, this study investigates competition between sinking and buoyancy-regulating phytoplankton species along the vertical water column. Species compete for light and nutrients (nitrogen and phosphorus) along heterogeneous depth gradients, making use of a modified Droop model. Specifically, we examine how seasonal stratification patterns influence phytoplankton dynamics and how physiological traits related to resource utilization and vertical movement strategies influence transient dynamics. Overall, this work provides new insights into the early development of phytoplankton blooms under changing lake stratification regimes.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Arthur ROSSIGNOL, AgroParisTech, Université Paris-Saclay (arthur.f.rossignol@gmail.com)

Authors:

Arthur F. Rossignol, AgroParisTech, 22 Place de l'Agronomie, 91120 Palaiseau, France.  (arthur.rossignol@agroparistech.fr)

Sabine Wollrab, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Department of Plankton and Microbial Ecology, Zur alten Fischerhuette 2, 16775 Stechlin, Germany.  (sabine.wollrab@igb-berlin.de)