SELECTION AND CONTROL OF DEBORAH NUMBERS IN PLANKTON ECOLOGY

The Deborah number (De) is widely used to characterize processes taking place in deforming continua. De = (the time scale of a process)/(the time scale of deformation). When De much greater than 1 the process thus takes place in a functionally fluid medium, but when De much less than 1 the regime is functionally solid. De has been used to refine concepts in three pelagic processes. Dispersion of dividing cells may be characterized by De, and may be regulated by means of Secretions. Dispersion of microzones by diffusion and shear is characterized. The characteristic time of microzones is shown to depend on the concentration. Because microzones smear out along the shear, to prevent nutrient-seekers and predators using them as scent trails, organisms may convolute their microzones by swimming, particularly across the shear. In a predator-prey model, it has been shown that when De, (shear rate).(time taken to swim radius of detection sphere), >2.6, not all the perceived prey is accessible. More economical bunting strategies and those allowing access to more of the perceived prey, require better sensory and navigational abilities. When De >2.6, the predator will perceive a greater flux of accessible prey when it swims across the shear than when it swims in the other two dimensions. De may help to understand many more biological processes in deforming media.