Carrie J. Thomas

Viable diatoms and chlorophylla in continental slope sediments off Cape Hatteras, North Carolina

Abstract Continental slope sediments off Cape Hatteras, North Carolina, were sampled by ☐ coring in late summer, 1992. The chlorophylla concentrations measured in sediments from 16 sites at depths ranging from 530 to 2003 m averaged 19.9 mg chla m−2, a concentration much higher than observed elsewhere on the eastern U.S. continental slope, indicating high depositional rates for microalgal material. The variability in the chlorophylla values suggests strong environmental heterogeneity at both small and large spatial scales in this slope habitat, probably a consequence of both topography and bioturbation. Viable diatoms were found in sediment samples across the range of depths sampled, and up to 14 cm deep in sediments, indicating high rates of deposition and bioturbation. Bulk sediment samples contained planktonic, tychopelagic and benthic diatoms, indicating that both phytoplankton and benthic microalgae from the continental shelf may be sources of organic matter for these slope sediments.

Transport and digestive alteration of uniformly 13C-labeled diatoms in mudflat sediments

Uniformly 13 C-labeled diatoms were used to elucidate the effect deposit feeders have on the distribution and composition of phytodetritus within the seabed. Mudflat infauna contained in microcosms reacted quickly to the emplacement of labeled diatoms onto the sediment-water interface by moving the phytodetritus nonlocally during feeding and hoeing activities. Although redistribution of tracer was rapid, not all infauna exposed to the tracer ingested it. Using four species of deposit-feeding annelids that had ingested the 13 C-labeled phytodetritus during the microcosm experiment, molecular-level, digestive alterations of 13 C-labeled diatoms were documented. Fecal material produced by the deposit feeders had 13 C amino acid signatures distinctly different from that of the diatom. Alterations in the amino acid composition of the diatom were correlated to the gut morphology and digestive physiology of the polychaete taxa.