Natural hydrodynamic stimuli

Abstract

Aquatic animals of all major phyla have developed sensory systems to perceive water movements, so-called hydrodynamic sensory systems. These water movements, or hydrodynamic stimuli, arise from a variety of sources. Some sources of hydrodynamic stimuli are biotic, such as predators, prey, and conspecifics, some are abiotic, such as wind, gravity that induces currents, and others. We have only relatively recently begun to take a closer look at these hydrodynamic stimuli with regard to the question how they may have formed the hydrodynamic sensory systems of aquatic animals during evolution. Hydrodynamic stimuli are measured with several different techniques, some of which are invasive, meaning that a sensor is inserted into the flow, some are noninvasive, such as optical and acoustical techniques. The laser-based technique of particle image velocimetry (PIV) has proven especially helpful. It is an optical technique that measures flow velocities not only in a single point, but simultaneously in hundreds or thousands of points in a selected layer of the fluid, and with more advanced modifications of the technique, even in a limited volume. Furthermore, the laser-based technique of laser Doppler velocimetry has contributed much to our understanding. In this chapter, naturally occurring hydrodynamic stimuli measured with these and other techniques are discussed, along with the advantages and shortcomings of the different experimental approaches.