Differing utilization of glucose and algal particulate organic matter by deep-sea benthic organisms of Sagami Bay, Japan

The fate of particulate and dissolved organic carbon in deep-sea benthic organisms was evaluated by in situ C-13-labeling experiments in the central part of Sagami Bay, Japan (water depth: 1453 m). C-13-labeled glucose and Chlorella sp. (Chlorophyta) were injected into a series of in situ culture cores and incubated for 0 to 9 d. Glucose was chosen as an example of labile dissolved organic matter in the pore water, and Chlorella sp. as an example of fresh algal material. Incorporation of both carbon sources by benthic foraminifera and metazoans was determined based on enrichment in C-13 of their bulk tissues. Archaeal incorporations were also evaluated by examining C-13-labeled lipid biomarkers. Chlorella sp. incorporation by foraminiferal species ranged from 0.0 to 40% of their biomass. Foraminiferal ingestion of algal materials varied markedly among the same species depending on body size or individual differences. All species incorporated glucose to similar extents, ranging from 0.1 to 0.3% of their biomass. Many foraminiferal species incorporated glucose faster than Chlorella sp. After 9 d of in situ incubation, 26.4, 1.7, 0.1, and 3.8% of added Chlorella sp. was detected in the bulk sediment, foraminiferal biomass, examined metazoan biomass, and respired CO2, respectively. The figures for glucose were 5.3, 0.04, 0.00, and 4.6%, respectively. Labile dissolved organic matter may serve as an accessible food source for benthic organisms and is quickly mineralized on the deep seafloor.