DEPOSIT AND SUSPENSION FEEDING IN OSCILLATORY FLOWS AND SEDIMENT FLUXES

We present a survey of feeding behavior of benthic organisms in oscillatory flow and sediment fluxes. These results are based on seventeen species from five phyla and several feeding guilds from an intertidal sandflat and the continental shelf of the Mid-Atlantic coast, U.S.A. General responses to oscillatory flows are: (1) nearly immediate change in feeding behavior or position of feeding appendage when flow is initiated, (2) decrease in feeding area for surface deposit feeders, often (3) alteration of feeding mode, and when anatomically permitted (4) rotation of feeding appendages to track flow direction. At high sediment fluxes, responses are functional group and morphology-specific. Organisms with one or two muscular feeding appendages continue to feed (e.g., Spio setosa, Spiochaetopterus oculatus and Emerita talpoida), while those with a crown of tentacles cannot (e.g., Pista palmata, Serpula vermicularis granulosa, and Terebella rubra). A continental shelf brittle star, Amphipholis squamata, ceases suspension feeding in high flows. Organisms with strong tentacles feed at the sediment surface in much restricted feeding area (Marenzelleria jonesi and Saccoglossus kowalevskii). Organisms with long, thin palps coil them helically and capture particles in near-bed flux (Spiochaetopterus oculatus and Spio setosa). Siphonate feeders maintain siphon tips near the sediment surface and continue pumping (Ensis directus, Mercenaria mercenaria and Tagelus plebeius). A sedentary omnivore (Diopatra cuprea) is able to capture food particles in low and moderate flow, but in high flows the tube opening is closed. Motile scavengers may either increase (Pagurus longicarpus) or decrease (Echinarachnius parma and Ilyanassa obsoleta) movement rate. Of all species studied, only the burrowing predatory starfish Astropecten americanus showed no change in behavior with respect to oscillatory flow. In addition, we report detailed quantitative changes in feeding behavior by a facultative suspension-feeding spionid polychaete Spio setosa and an obligate deposit-feeding terebellid polychaete Terebella rubra which indicate hysteresis or time-dependence in the response to flow and sediment flux. We attempt a summary of responses by functional group and morphology and suggest that new descriptive terms combining low-flow feeding behavior and morphology are needed to characterize feeding modes adequately. Our analysis suggests that it is important to consider the possible presence of flow and flux micro-environments, an individual organisms's variability, flow history and the various time scales of behavioral responses and other biological rate processes. There is a current need for dynamic feeding models that incorporate these factors as well as for experimental tests of the derived predictions.