Field measurements of the fluid and sediment-dynamic environment of a benthic deposit feeder

Field measurements of flow and sediment transport at an intertidal site in False Bay, San Juan Island, Washington, U.S.A., revealed an environment dominated by wind wave-generated oscillatory flows and discrete sediment suspension events. Time series data showed that within a few tenths of a second, near-bottom suspended sediment concentrations can rise to 10 g l–1. These rapid erosion events are correlated with peak wave velocities and are followed by a more gradual (tens of seconds) decline in sediment concentration due to settling and advection. Large suspension events mixed detect able quantities of sediment to a height of 20 cm above the bottom. Flow and sediment transport rates are controlled by local weather and vary on time scales ranging from that of individual waves to that of atmospheric storm systems and seasonal changes in weather patterns. Advection of sediment can exceed individual deposit feeding rates by a factor of 103–104. An empirical relationship developed from weather records, together with previously published observations of detrital transport, suggests that sediment transport is rarely small enough in magnitude to be ignored as a source of food particles for surface deposit- and suspension-feeding spionid polychaetes like Pseudopolydora kempi japonica.