An object-oriented model for the prediction of turbulence effects on plankton

In this work, we propose an object-oriented individual based model for the analysis of the effects of turbulence on the interactions and the behaviour of planktonic organisms at microscopic scales. We model homogeneous isotropic turbulence by adopting a kinematic simulation of the flow, where the velocity field is prescribed as a combination of a large number of unsteady random Fourier modes.

As for the biotic component we use special contact classes to build a “memory” of an individual particle, allowing the storage of frequency, duration and identity of each interaction experienced by the individuals throughout the whole time span of the simulation. This, in turn, allows classifying the different interactions.

We tested our model on the classical problem of the encounter rate between a consumer and a food particle. The model reproduces well the results of analytical bulk models or of previous numerical simulations, which demonstrated the enhancement of contact numbers due to the turbulent flow especially for slow moving or ambushing consumers.

The results also highlight that a critical parameter in the encounter is the duration of the contacts. This suggests that the evident decrease in clearance rate of grazers in experimental setups in the high turbulence range may be significantly affected by the decrease of the encounter duration and its impact on detection, capturing and handling the prey.

As a matter of fact, the encounter duration sets a typical scale dependent on the swimming speed, the typical scale of turbulence, and the encounter radius, beyond which the enhancement of useful encounter rates becomes negligible.