Meeting Abstract
The hydrodynamic forces generated by breaking waves are one of the greatest environmental stressors experienced by organisms residing in the rocky intertidal zone of wave-swept shores. Although past studies have developed methods to measure water velocity in the field on the scale of centimeters—a scale relevant to relatively large organisms such as barnacles and limpets—measuring at finer scale has not been possible because the delicate laboratory instrumentation usually used for this purpose is unfit for the extreme physical conditions of the intertidal zone. Flow at sub-millimeter scales is important to characterize, however, as it affects the distribution of small benthic organisms as well as larvae and spores seeking to settle on new surfaces. We have designed a pressure block able to continuously measure flow 250 microns above the substrate. We are also able to manipulate the topography immediately surrounding the pressure block to determine the effectiveness of apparent hydrodynamic shelters (e.g., the inside of an empty barnacle test or the interstices of a mussel bed) at damping local water velocities. Data show that the flow environment across a flat plate at this height can exhibit extremely high velocities (greater than 5 m/s) with great frequency (several occurrences per minute). Local topography can reduce water velocities by up to 50%, so organisms within these hydrodynamic shelters would still be exposed to high flows. These measurements suggest that organisms of this size range can not hide from hydrodynamic forces by residing in the boundary layer.
