Life in transition: Balancing inertial and viscous forces by planktonic copepods

Copepods (1-10 mm aquatic crustaceans moving at 1-1000 mm s(-1)) live at Re ynolds numbers that vary over 5 orders of magnitude, from 10(-2) to 10(3). Hence, they live at the interface between laminar and turbulent regimes and are subject to the physical constraints imposed by both viscous and inerti al realms. At large scales, the inertially driven system enforces the domin ance of physically derived fluid motion; plankton, advected by currents, ad just their life histories to the changing oceanic environment. At Kolmogoro v scales, a careful interplay of evenly matched forces of biology and physi cs occurs. Copepods conform or deform the local physical environment for th eir survival, using morphological and behavioral adaptations to shift the b alance in their favor. Examples of these balances and transitions are obser ved when copepods engage in their various survival tasks of feeding, predat or avoidance, mating, and signaling. Quantitative analyses of their behavio r give measures of such physical properties of their fluid medium as energy dissipation rates, molecular diffusion rates, eddy size, and eddy packagin g. Understanding the micromechanics of small-scale biological-physical-chem ical interactions gives insight into factors influencing largescale dynamic s of copepod distribution, patchiness, and encounter probabilities in the s ea.