Meeting Abstract
Fouling communities on ships and docks develop as planktonic larvae of invertebrates settle onto them from flowing water. Competent larvae of the tubeworm Hydroides elegans settle and metamorphose only on biofilmed surfaces and are abundant early colonists in fouling communities. They were used to determine if the behavior of microscopic larvae carried in ambient water flow can affect their contacts with surfaces representing early stages of fouling community succession: clean flat surfaces, flat biofilm, or biofilm on rough worm tubes. Most flume studies of larval settlement are done in unidirectional flow along a floor, but we videotaped the motion of larvae near both ceiling and floor of a small flume in which we mimicked fine-scale flow measured near surfaces in a harbor: unidirectional current or small waves superimposed on a current. In flowing water near surfaces, larval motions can be due to active behavior and passive transport. Live larvae moved up and down across the boundary layer more than passive dead larvae, and a higher percent of live larvae contacted surfaces. Live larvae “bounced” along a surface after landing while dead larvae did not, so live larvae touched a surface more times per distance they were carried by the flow. Contacts by live larvae on clean surfaces were shorter than on biofilm, but did not differ between flat and rough biofilmed surfaces. Touch durations of live larvae on biofilm were shorter in flow than in still water, but adding small waves to a current did not affect larval contacts. Similar patterns occurred for ceiling and floor. Thus, active behavior of larvae swept past surfaces by flow can affect how they contact those surfaces.
