Phylogeography of the Seaweed Ishige Okamurae (Phaeophyceae): Evidence for Glacial Refugia in the Northwest Pacific Region

[[abstract]]Although benthic marine algae are essential components of marine coastal systems that have been inXuenced profoundly by past and present climate change, our knowledge of seaweed phylogeography is limited. The brown alga Ishige okamurae Yendo occurs in the northwest PaciWc, where it occupies a characteristic belt in the exposed intertidal zone. To understand the patterns of genetic diversity and the evolutionary history of this species, we analyzed mitochondrial cox3 from 14 populations (221 individuals) throughout its range. The 17 haplotypes found in this study formed Wve distinct clades, indicating signiWcant genetic structure. The high diVerentiation and number of unique (private) haplotypes may result from the recolonization of the species from glacial refugia. Three putative refugia, each with high genetic diversity, were identiWed: southern Korea (including Jeju Island), northern Taiwan, and central PaciWc Japan. Recolonization of I. okamurae was probably determined by ocean currents and changes in sea level during the last glacial period