ABSTRACT-Tracer experiments using '"-labeled diatoms Thalassiosira pseudonana were carried out at two 850 m sites (1 off Cape Fear and I11 off Cape Hatteras) on the North Carolina. USA, slope to examine patterns of macrofaunal consumption of fresh phytodetritus. Experiments examined the influence of taxon, feeding mode, body size and vertical position within the sediment column on access to surfic~al organic matter. 6IJC measurements were made on macrofaunal metazoans and agglutinating protozoans from background sediments and from sed~ment plots in which 13C-labeled diatoms were depos~ted and then sampled 0.3 h, 1 to 1.5 d , 3 1170 and 14 mo later. Significant between-site differences were observed in background 6I3C signatures of sed~ments, metazoans, and large, agglutinating protozoan~, with values 2 to 3 x 0 lower at Site I11 than at Site I. Background 6I3C signatures also varied as a function of taxon and of vertical position in the sediment column at Site 111. The background 613C value of carnivores was higher than that of surface-deposit feeders among Site I annelids, but no annelid feeding-group differences were observed at Site 111. 6I3C data from short-term (1 to 1.5 d) experiments revealed rapid diatom ingestion, primarily by agglutinated protozoans and annelids at Site I and mainly by annelids at Site 111. Selective feeding on diatoms was exhibited by paraonid polychaetes, especially Aricidea spp. Exceptionally high uptake and retention of diatom C also was observed in the maldanid Praxjllella sp., the nereid Ceratocephale sp. and several other surfacedeposit feeding polychaetes. After 14 mo, little of the diatom I3C remained at Slte 111, but high concentrations of the tracer were present in annelids and agglutlnatlng protozoans at Site 1. At both sites, nonannelid metazoans and subsurface-deposit feeding annelids exhibited the least uptake and retention of diatom C. Our hypotheses that large-bodied taxa and shallow-dwelling infauna should have greatest access to freshly deposited organic matter were not borne out. Some small, deep-dwelling taxa acquired label more readily than large or near-surface forms. Differences in tracer fates between sites reflected greater vertical mixing at Site 111. These results indicate heterogeneity in benthic processes along the, Carolina margin, but suggest that labile organic matter is consumed qu~ckly at both sites Because most of the taxa found to consume freshly deposited diatoms in these r~xpenments are typical of bathyal settings, we infer that phytodetritus reaching the seabed in margin environments is rapidly processed by protozoan and metazoan components of the benthlc fauna.

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graduating with high honors. He spent the next year working as a biohazard laboratory technician for the Center for Applied Aquatic Ecology at North Carolina State University. In 2002 he began attending NCSU as a full time graduate student in the Department of Marine, Earth and Atmospheric Sciences and has spent two years on the work contained in this document. iii