Hydrodynamic facilitation of gregarious settlement of a reef-building tube worm.

Experiments testing the effects of hydrodynamic processes and chemical cues on substrate selection were conducted with larvae of the marine tube worm Phragmatopoma lapidosa californica. In flume experiments, larvae were presented an array of sand treatments, including two substrates previously shown to induce metamorphosis in this species, under fast and slow flow regimes. Larvae preferentially metamorphosed on the inductive substrates in both flows. Delivery to the array was higher in fast flow because larvae tumbled along the bottom, whereas in slow flow, larvae were observed swimming in the water column. Thus, in addition to chemical cues, behavioral responses to flow conditions may play an important role in larval recruitment to the benthos.