Community composition, distribution, and contribution of microbenthos in offshore sediments from the Yellow Sea

Abstract: We investigated the spatial distribution and composition of microbenthos in the seafloor sediments from 48 stations in the Yellow Sea using epifluorescence microscopy and quantitative protargol staining techniques. The bacterial abundance ranged from 2.4×108 to 1.9×109 cellscm−3 in the wet sediment, about three orders of magnitude higher than that of phototrophic (PNFs, from 6.4×105 to 8.8×106 cellscm−3) and heterotrophic nanoflagellates (HNFs, from 5.8×104 to 5.9×106 cellscm−3) and four orders of magnitude higher than that of cyanobacteria (from 2.3×104 to 2.3×106 cellscm−3) in the upper 5cm of sediments. The abundance of diatoms varied greatly, from 3–1.1×105 cellscm−3 in the upper 8cm of sediments, whereas those of heterotrophic microflagellates (HMFs, 1–182cellscm−3) and ciliates (1–221cellscm−3) were less varied and lower. The biomass partitioning indicates the primary importance of benthic bacteria (50.3μgCcm−3 on average), followed by PNFs (40.7μgCcm−3), HNFs (19.3μgCcm−3), and finally by cyanobacteria (8.8μgCcm−3). Benthic diatoms (0.8μgCcm−3), ciliates (0.15μgCcm−3), and HMFs (0.03μgCcm−3) contribute relatively small fractions to the total biomass of the microbenthos. About 95% of diatoms, 77% of ciliates, and 56% of HMFs were distributed in the upper 2cm of sediments, whereas no distinct vertical distributions were observed for bacteria, cyanobacteria, PNFs, and HNFs. The microbenthos are quantitatively important in the shallow seafloor, wherein their main components have an average abundance three orders of magnitude higher than the corresponding planktonic organisms in the same sea area. Our estimates indicate that pico-sized phytobenthos might contribute a large proportion to the primary production. Benthic ciliates and heterotrophic flagellates contribute about 90% to the estimated combined metabolic rate of micro- and meiobenthic consumers in the whole sea area, with nanoheterotrophs accounting for the majority. The data suggest the potential for the rapid primary and secondary production of microbenthos and detrital utilization in the shallow seafloor sediments of the Yellow Sea. [Copyright &y& Elsevier]