UTILIZATION OF DEPOSITED AND SUSPENDED PARTICULATE MATTER BY BENTHIC INTERFACE FEEDERS

The polychaetes Boccardia pugettensis and Pseudopolydora kempi japonica, like many invertebrates, switch from deposit feeding to passive suspension feeding as the flux of suspended particles increases. We tested the hypothesis that this behavior is energetically profitable because suspended particles have greater food value. In laboratory experiments, animals were restricted to deposit feeding, restricted to suspension feeding, or allowed to do both. Suspended particles had greater mass-specific concentrations of total organic matter, organic C, labile protein, N, and Chl a. Both species fed at significantly reduced volumetric rates when suspension feeding, but the suspension feeding rate of Pseudopolydora (only 19% of the deposit-feeding rate) was more depressed than that of Boccardia (45-75% of deposit-feeding rate). Pseudopolydora's growth rate was lower when suspension feeding (0.3-0.8% AFDW d-1) relative to deposit feeding (2.8-3.8% AFDW d-1). In contrast, Boccardia grew as well or better when suspension feeding (2.7-7.6% AFDW d-1) relative to deposit feeding (2.2-5.0% AFDW d-1). Despite similar morphologies and behaviors, we found unexpected differences in the abilities of these species to utilize particulate organic matter under varying boundary-layer conditions.