Particle selectivity, gut volume, and the response to a step change in diet for deposit-feeding polychaetes
Limnol. Oceanogr., 44(4), 1999, 1132-1138 | DOI: 10.4319/lo.19220.127.116.112
ABSTRACT: 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.