Two clades of Ostreococcus were thought to be distinguished in the environment by their adaptation to light intensities, with the high-light ecotypes being detected at warm oligotrophic sites whereas the low-light ecotypes were present in cooler mesotrophic and coastal waters (Rodriguez et al., 2005). The YSWC originated from the Kuroshio but rich in nutrients, thus it is dif fi cult to speculate which clade dominated or coexist. In the future, using fl uorescence in situ hybridization with primer-probes (Demir-Hilton et al., 2011) may fi nd out the difference in distributions of these two clades in the central YS.