The demonstrated bias of both macrobenthos and fluids to mobilize low-density particles leads to their potential importance as nutritional materials in benthic systems. We fractionated sediments from three coastal regions into low- and high-density separates, and examined both their organic geochemical characteristics and effects on ingestion rates of a deposit feeder. The low-density separates were highly enriched in total organic matter relative to the high-density phases. Enzymatically hydrolyzable protein concentrations in low-density separates were as much as 57-fold higher than the corresponding high-density separates, though some samples from Puget Sound and the Mediterranean Sea showed no enrichment at all. Low-density phases without nutritional enrichments were usually composed of woody debris. In spite of the organic richness of the low-density phase, it makes up no more than a minor fraction of either total sedimentary organic matter or its nutritional component. Addition of anomalously high concentrations of low-density materials to sediments caused a deposit-feeding spionid polychaete to reduce ingestion rates.