INTERACTIONS OF MARINE SEDIMENT TRANSPORT WITH DEPOSIT FEEDING AND MICROBIAL GROWTH (DETRITIVORY, FORAGING THEORY, FALSE BAY, WASHINGTON)

At least five dimensionless variables are needed to predict the relative importance of advected and locally-produced food resources to surface deposit feeders. Particle mixing in bedforms and beneath waves dramatically affects the pool of available particles. Derived dimensionless parameters place existing deposit-feeding models in an environmental context in addition to characterizing the benthic environment in terms of sediment transport effects on food resources. Experiments demonstrated that accumulation of fecal pellets in the feeding area of a surface-deposit feeding polychaete, Pseudopolydora kempi japonica, depresses feeding rate. Removal of pellets derepresses feeding rate even under very crowded conditions. Spatial scales of feeding radius and interworm distance as well as temporal scales of frequency of egestion and removal of fecal material by sediment transport are important determinants of feeding rate. Field measurements of the flow and sediment transport at an intertidal site in False Bay, San Juan Island, Washington, U.S.A., revealed an environment dominated by oscillatory flow and discrete sediment suspension events. Flow and sediment transport rates are controlled by local weather and vary on a number of time scales from seconds to seasons. Advection of sediment can exceed individual deposit-feeding rates by a factor of 10('3)-10('4). Empirical extrapolation from weather records suggests that sediment transport is rarely small enough in magnitude to be ignred as a source of food particles for a surface deposit feeder like Pseudopolydora. Laboratory experiment demonstrated that bedload sediment transport at high rates can significantly remove epipsammic bacteria and diatoms from exposed grain surfaces during sediment transport. Flume results indicated that plane-bed transport for relatively long periods of time can decrease microbial abundances. Storm-induced transport events at False Bay caused no decrease in field microbial abundances, but transport rates at False Bay were low compared to those causing abrasion in laboratory experiments. Several characteristics of the transport process, in addition to mass flux, were predicted to be important in determining abrasion rate.