Lagrangian model of copepod dynamics: Clustering by escape jumps in turbulence
Abstract
Planktonic copepods are small crustaceans that have the ability to swim by quick powerful jumps. Such an aptness is used to escape from high shear regions, which may be caused either by flow perturbations, produced by a large predator (i.e., fish larvae), or by the inherent highly turbulent dynamics of the ocean. Through a combined experimental and numerical study, we investigate the impact of jumping behavior on the smallscale patchiness of copepods in a turbulent environment. Recorded velocity tracks of copepods displaying escape response jumps in still water are here used to define and tune a Lagrangian copepod (LC) model. The model is further employed to simulate the behavior of thousands of copepods in a fully developed hydrodynamic turbulent flow obtained by direct numerical simulation of the NavierStokes equations. First, we show that the LC velocity statistics is in qualitative agreement with available experimental observations of copepods in turbulence. Second, we quantify the clustering of LC, via the fractal dimension D_{2}. We show that D_{2} can be as low as ∼2.3 and that it critically depends on the shearrate sensitivity of the proposed LC model, in particular it exhibits a minimum in a narrow range of shearrate values. We further investigate the effect of jump intensity, jump orientation, and geometrical aspect ratio of the copepods on the smallscale spatial distribution. At last, possible ecological implications of the observed clustering on encounter rates and mating success are discussed.
 Publication:

Physical Review E
 Pub Date:
 April 2016
 DOI:
 10.1103/PhysRevE.93.043117
 arXiv:
 arXiv:1601.01438
 Bibcode:
 2016PhRvE..93d3117A
 Keywords:

 Physics  Fluid Dynamics
 EPrint:
 13 pages, 9 figures