Limnol. Oceanogr., 44(4), 1999, 1132–1138

We performed a series of experiments to examine the aspects of deposit feeding that were relevant to studies of resource variability over short time scales. We examined particle-size selectivity, gut volume, gut residence time, and the response to a change in diet in three polychaete species: Spiochaetopterus oculatus, Spio setos and Marenzelleria viridis. All three species were particle-size selective and had similar gut volumes and gut residence times. Thus, measurements of bulk sediment characteristics are largely irrelevant to the studies of their nutrition. In response to a step change in diet, changes in the egestion rate were accomplished by smooth transitions between steady-state rates occurring over 1 to 2 h. The form of this modulation suggests that these organisms do not respond to changes in diet by temporarily retaining or flushing the material in the gut in order to increase digestive yield. The time scale of the response to a change in diet provides evidence for a foregut/midgut feedback mechanism for inducing changes in feeding rate due to sediment food concentration. If the time required to modulate the feeding rate to a new steady state is more rapid than the time scale of food-resource variability in the field, it is unlikely that a response other than a gradual transition to a new ingestion rate would provide a significant advantage. Deposit-feeding marine polychaetes live in a temporally and spatially heterogeneous environment. Previous results have shown that food resources in surficial sediments can change on a daily time scale in response to storm-associated sediment transport (Miller et al. 1984; Bock and Miller 1995). Specifically, feeding areas can be depleted with respect to sedimentary organic matter (Miller et al. 1984; Bock and Miller 1995) and preferred particle sizes (Luckenbach et al. 1988). On large spatial scales, sediment transport can move organic matter many meters (Levinton and McCartney 1991). On small spatial scales, individual grains in a sedimentary deposit may vary in terms of grain size and organic matter per particle (Mayer 1994a,b). Deposit feeders are known to feed selectively on the basis of grain size and organic coating when presented with a choice (Taghon 1982; Self and Jumars 1988). Thus, the concentration and composition of the organic matter ingested can be highly variable in space and time and is not necessarily equivalent to the ambient, or bulk, sediment found in their feeding areas. Organisms feeding at the sediment–water interface respond rapidly to changes in fluid flow and particle transport. Organisms capable of feeding on suspended and bedload material will do so when exposed to nutritious particles in transport (e.g., Dauer et al. 1981; Nowell et al 1989; Miller et al 1992; Bock and Miller 1996, 1997). Dedicated suspension feeders often alter their feeding strategy when flow and particle transport conditions change (e.g., Bricelj 1984; Bricelj et al. 1984; Rhoads et al. 1984; Bayne et al. 1987; Grizzle and Lutz 1989; Grant et al. 1990; Ward et al. 1996). Dedicated deposit feeders may adjust the size of their feed1Present address: University of Maine, Darling Marine Center, Walpole, Maine 04573.