Spatial heterogeneity of benthos on the Carolina continental slope: large (100km)-scale variation

The northernmost site (Site III, off Cape Hatteras, NC) had macrofaunal abundances (>55 000m^-2) higher than any previously recorded from 850m, and significantly higher than those at site II (off Cape Lookout, NC) (21 319 m^-2) or Site I (off Charleston, SC) 9438m^-2). Trends in macrofaunal abundance did not follow those of sediment TOC (total organic carbon), but agreed well with estimates of total carbon flux. Sediments at Site III are mixed 2-6 times faster than at the other sites. The authors estimated carbon flux to be 0.6, 20 and >70 g C m^-1yr^-1 at Sites I, II and III, respectively. The flux of metabolizable carbon was greater at Site III. Polychaetes, which comprised 43, 74 and 65% of the fauna at Site I, II and III, respectively, exhibited lower diversity higher dominance, and a completely different species composition at Site III. Scalibregma inflatum and Aricidea quadrilobata comprised 33% of total macrofauna at Site III, but were absent at Sites I and II. The species composition, high dominance, and prevalence of juveniles among polychaetes at Site III suggests a response to organic enrichment. Enrichment of the Site III benthos is attributed to physical oceanographic and geophysical causes, including Gulf Stream-induced upwelling, a confluence of currents focused by bottom topography, and lateral inputs resulting from mass wasting processes. Sites I and II exhibited considerable overlap in microbial counts, polychaete species composition, dominance and diversity patterns. -from Authors