# Copepods encounter rates from a model of escape jump behaviour in turbulence

## TL;DR

This study models copepod escape jumps in turbulent flow, revealing that such behaviour can significantly increase encounter rates, but only under certain turbulence conditions, with implications for understanding plankton interactions.

## Contribution

The paper introduces a Lagrangian copepod model that simulates escape jumps in turbulence, quantifying their impact on encounter rates and constraints imposed by turbulence timescales.

## Key findings

- Encounter rate can increase up to 100 times due to escape jumps.
- Enhanced encounter rates are limited by turbulence dissipation time-scale.
- Mechanical escape reactions are constrained by ocean turbulence parameters.

## Abstract

A key ecological parameter for planktonic copepods studies is their interspecies encounter rate which is driven by their behaviour and is strongly influenced by turbulence of the surrounding environment. A distinctive feature of copepods motility is their ability to perform quick displacements, often dubbed jumps, by means of powerful swimming strokes. Such a reaction has been associated to an escape behaviour from flow disturbances due to predators or other external dangers. In the present study, the encounter rate of copepods in a developed turbulent flow with intensity comparable to the one found in copepods' habitat is numerically investigated. This is done by means of a Lagrangian copepod (LC) model that mimics the jump escape reaction behaviour from localised high-shear rate fluctuations in the turbulent flows. Our analysis shows that the encounter rate for copepods of typical perception radius of ~ {\eta}, where {\eta} is the dissipative scale of turbulence, can be increased by a factor up to ~ 100 compared to the one experienced by passively transported fluid tracers. Furthermore, we address the effect of introducing in the LC model a minimal waiting time between consecutive jumps. It is shown that any encounter-rate enhancement is lost if such time goes beyond the dissipative time-scale of turbulence, {\tau}_{\eta}. Because typically in the ocean {\eta} ~ 0.001m and {\tau}_{\eta} ~ 1s, this provides stringent constraints on the turbulent-driven enhancement of encounter-rate due to a purely mechanical induced escape reaction.