Two Gram-negative, motile, non-spore-forming and moderately halophilic rods (strains SW-47(T) and SW-49) were isolated from sea water of the East Sea in Korea and subjected to a polyphasic taxonomic study. The two strains grew optimally between 30 and 37 degrees C, and grew at 4 and 44 degrees C but not at temperatures above 45 degrees C. They grew optimally in the presence of 2-5 % (w/v) NaCl, but did not grow in the absence of NaCl. Strains SW-47(T) and SW-49 had ubiquinone-8 (Q-8) as the predominant respiratory lipoquinone and C(16 : 1) omega7c and/or iso-C(15 : 0) 2OH, C(16 : 0) and C(18 : 1) omega7c as the major fatty acids, which are consistent with the corresponding data for Alteromonas macleodii. The DNA G+C contents of strains SW-47(T) and SW-49 were 45 and 44 mol%, respectively. Strains SW-47(T) and SW-49 showed a high level of 16S rDNA sequence similarity (99.9 %) and a mean level of DNA-DNA relatedness of 96.5 %. Phylogenetic analyses based on 16S rDNA sequences showed that the two strains form a coherent cluster with A. macleodii. Strains SW-47(T) and SW-49 exhibited levels of 16S rDNA sequence similarity of 99.3 and 99.1 %, respectively, with A. macleodii DSM 6062(T) and of less than 89.4 % with other species used in the phylogenetic analyses. Alteromonas fuliginea CIP 105339(T) was found to be more closely related to the genus Pseudoalteromonas than to the genus ALTEROMONAS: On the basis of phenotypic properties and phylogenetic and genomic data, strains SW-47(T) and SW-49 represent a new species of the genus Alteromonas, for which the name Alteromonas marina (type strain SW-47(T)=KCCM 41638(T)=JCM 11804(T)) is proposed.