Abstract
The influence of storms on particulate food resources on an intertidal sandflat (Cape Henlopen, Delaware, USA) was investigated by contrasting measurements taken during calm conditions and storm conditions. Storms exhibited elevated fluid velocities dominated by an oscillatory component, doubled seston concentrations increasing toward the bed and increased sediment transport rates. We also measured the concentration of sedimentary protein and chlorophyll (as proxies of food resources) inside and outside the feeding areas of two polychaete species, the surface deposit feeder Marenzelleria viridis (Verrill) and the mode-switching facultative suspension feeder Spiochaetopterus oculatus (Webster). During calm conditions, protein and chlorophyll were significantly depleted from feeding areas of the deposit feeder, while only protein was significantly depleted from feeding areas of the mode switcher. Neither protein nor chlorophyll was depleted in storm samples. These data are direct evidence for variable centimeter-scale, food resource gradients in the field. We also measured changes in the composition of the suspended load, bedload and surficial sediments before, during and after the passage of storms. Wave height, suspended solids, suspended particulate organic matter (POM) and bedload transport were increased during storms. There were changes in the quality of the bedload material, with the protein and chlorophyll concentrations being greatest during calm weather. These changes could be attributed to dilution with the bulk sediment during sedimentologically active periods. At the transition from storm conditions to calm conditions, the protein concentration in the surficial sediments increased temporarily by a factor of two, returning to prestorm levels by the next day. This spike was attributed to the deposition of fine-grained material which was resuspended during storms. Field-preserved specimens showed that the deposit feeder Marenzelleria viridis changed its feeding behavior, with gut fullness, and presumably the feeding rate, highest during calm conditions.
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