A gram-stain-negative, aerobic, ovoid or short rod-shaped, and non-motile strain, designed G7(T) was isolated from a tidal flat sample collected from the coast of East Sea in Zhoushan, China. Strain G7(T) grew at 4-40 A degrees C and pH 6.0-9.0 (optimum, 28 A degrees C and pH 7.5) and with 0-7% (w/v) NaCl (optimum, 1%). The predominant respiratory quinone was Q-10 and the major fatty acids (> 10%) identified were C-18:1 omega 7c, C-16:0 and summed feature 3 (C-16:1 omega 7c and/or C-16:1 omega 6c). The polar lipids of strain G7(T) consisted of phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, and four unidentified lipids. The genomic DNA G+C content was 56.7 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain G7(T) formed a distinct lineage belonging to the Roseobacter clade of the family Rhodobacteraceae. On the basis of morphological, physiological, and chemotaxonomic characteristics, together with the results of phylogenetic analysis, strain G7(T) is described as a novel species in a new genus, for which the name Aestuarium zhoushanense gen. nov., sp. nov. (type strain G7(T) = MCCC 1K03229(T) = KCTC 52584(T)) is proposed.