Abstract

We examined the interactive effects of fluid flow, bed characteristics and suspended load on the feeding behavior of four species of marine polychaetes. Two species of obligate deposit feeders (Marenzelleria viridis and Ampharete parvidentata) and two species of palp-coiling facultative suspension feeders (Spiochaetopterus oculatus and Spio setosa) were exposed to flow and sediment-bed treatments that served to decouple fluid flow and particle flux. We employed low (no particle transport), medium (transport of flocs only) and high (transport of sand) flow speeds in factorial treatments of natural sediment, winnowed bed (flocs removed), armored bed (no sand transport at high flows), and armored bed plus fines (flocs added). For each species, worms were exposed to an increasing (low, medium and high) and then decreasing (high, medium and low) flow leg for each bed treatment. We recorded visual observations of animal behavior of the four polychaete species. We found little systematic response to flow and bed differences in the two obligate deposit feeders. When fine material was present, one of the two species exhibited higher variability in time spent deposit feeding, possibly responding to small-scale depositional pockets enriched with fine particles and organic matter. For both facultative suspension feeders, there was an increase in time spent suspension feeding with increasing flow and suspended particle concentrations. Percent suspension feeding was also greater on the decreasing flow legs in treatments with fine material available for suspension. Exploratory analyses of the data reveal a direct relationship between time spent suspension feeding and the flux of suspended high quality organic matter. For both species, compositional parameters of particulate nitrogen and enzymatically available amino acid concentrations were the best correlates of suspension feeding behavior.

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