ABSTRACT
This study examined the hydrodynamic limits to the bathymetric distribution of the Pacific sand dollar Dendraster excentricus. The velocity at which Dendraster gets swept away by water flow (critical velocity) was measured in a recirculating flow tank using preserved specimens placed in various postures on or in the sediment. The critical velocity for the inclined orientation parallel to the flow was the highest (mean ± 95% confidence limits = 0.40 m/s ± 0.03), but did not differ significantly from that measured for specimens with the oral surface down on the sediment (0.37 m/s ± 0.04). I used wave height and wave period information from locations along the western coast of North America to estimate horizontal flow velocities at different depths using linear wave theory, and compared them to the critical velocity to predict the expected limits of sand dollar distribution.
