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Investigating the entire species composition of the microorganisms is crucial to understand their roles in the biogeochemical cycles. Metagenomic DNA was extracted from six intertidal sediment samples along the Liaodong Bay of Bohai Sea, China, and was sequenced which yielded a total of 64,496 high-quality sequences from 83,485 reads, with an average read length of 463 bp. The sequences were assigned to 20,718 operational taxonomic units (OTUs) which belong to 42 phyla, 90 classes and 376 genera. At the different taxonomic levels, both the dominants and their abundances varied significantly among the six sites. Phylum Proteobacteria predominated in all the six samples, however, not only the abundance of this phylum varied significantly but also the proportions of Alpha-, Beta-, Gamma-, and delta- and epsilon-Proteobacteria varied greatly. The site sediment median grain size and dissolved oxygen (DO) revealed to be key factors regulating the observed significant differences in the bacterial community between sampling sites. In addition, the bacterial composition might be more sensitive than the richness and diversity to the studied environmental conditions.

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In recent decades, China has undergone an impressive development, which has produced increasing human pressures including coastal degradation. Bohai Bay, located in the west of the Bohai Sea (north of China), has been affected by various human pressures, including waste water discharges, land reclamation and oil exploitation. To monitor the effects of these pressures on this ecosystem, benthic macroinvertebrates and environmental variables (dissolved oxygen, nutrients, metals, etc.) were sampled in 2009 and 2011. To assess the ecological status of the benthic communities, the AZTI Marine Biotic Index (AMBI) and multivariate-AMBI (M-AMBI) were used, including both density and biomass in the calculation. This is the first research in which M-AMBI based on biomass (M-bAMBI) is applied. Both methods showed that the nearshore areas, especially close to the Haihe and Jiyun estuaries, were affected by human pressures, with a clear gradient of decreasing impacts offshore. The ecological status as assessed using density and biomass was quite similar. Significant relationships were also found between both methods and environmental variables. The use of AMBI and M-AMBI, based upon density and biomass, in assessing the ecological status of water bodies in China seems to be promising.