Patchiness in a minimal nutrient-phytoplankton model.

Area of Science:

• Ecology
• Mathematical Biology
• Environmental Science

Background:

• Aquatic ecosystems exhibit complex spatial patterns influenced by nutrient dynamics and biological interactions.
• Understanding phytoplankton distribution is crucial for assessing ecosystem health and eutrophication levels.

Purpose of the Study:

• To develop and analyze a minimal two-component model of nutrients and phytoplankton.
• To investigate the emergence of spatial patterns, including patchiness, under varying nutrient input and grazing pressures.
• To explore the potential of phytoplankton spatial patterns as indicators of aquatic ecosystem eutrophication.

Main Methods:

• A minimal two-component model incorporating Holling type II functional responses for nutrient uptake and zooplankton grazing.
• Analysis of the mean-field model to identify bistability and limit-cycle oscillations.
• Application of reaction-advection-diffusion equations to simulate spatial pattern formation under turbulent mixing.
• Systematic variation of parameters, including nutrient input rate and maximum zooplankton feeding rate.

Main Results:

• The model demonstrates bistability and limit-cycle oscillations in the absence of diffusion and advection.
• Turbulent stirring and mixing, combined with biological interactions, drive spatial pattern formation in the reaction-advection-diffusion model.
• Increasing nutrient input leads to a transition from phytoplankton extinction to filamentous patterns, patchiness, and homogeneous distributions.

Conclusions:

• Phytoplankton spatial patterns are dynamically generated by nutrient availability, grazing, and physical mixing processes.
• The model successfully reproduces diverse spatial patterns, including patchiness, observed in aquatic ecosystems.
• Phytoplankton spatial distribution serves as a valuable indicator for evaluating the eutrophication status of aquatic environments.