Predator-prey plankton dynamics in turbulent wakes behind islands

TL;DR

This study investigates how turbulent flows around islands influence plankton populations, revealing that flow dynamics critically affect biomass distribution, bloom formation, and patchiness, with local flow structures causing plankton accumulation in filamentary regions.

Contribution

It provides new insights into the effects of multiscale turbulence and island shape on plankton dynamics using direct numerical simulations, extending previous simpler flow models.

Findings

Plankton biomass and dynamics depend on advective and biological time scale relations.

Flow structures cause plankton to accumulate in filamentary regions.

Main population features are weakly affected by Reynolds number and obstacle shape.

Abstract

Plankton constitutes the productive base of aquatic ecosystems and plays an essential role in the global carbon cycle. The impact of hydrodynamic conditions on the biological activity of plankton species can manifest in a variety of different ways and the understanding of the basic effects due to multiscale complex flows still appears incomplete. Here, we consider a predator-prey model of plankton dynamics in the presence of a turbulent flow past an idealized island, to investigate the conditions under which an algal bloom is observed, and the resulting patchiness of plankton distributions. By means of direct numerical simulations, we explore the role of the turbulent intensity and of the island shape. In particular, we focus on population variance spectra, and on their relation with the statistical features of the turbulent flow, as well as on the correlation between the spatial distribution of the planktonic species and velocity field persistent structures. We find that both the average biomass and local plankton dynamics critically depend on the relation between advective and biological time scales, confirming and extending previous results obtained in simpler flow settings. We further provide evidence that, in the present system, due to local flow action plankton accumulates in localized filamentary regions. Small turbulent scales are found to impact the statistics of plankton density fields at very fine scales, but the main global features of the population dynamics only weakly depend on the Reynolds number and are also found to be remarkably independent of the geometrical details of the obstacle.