Historical isolation and paleoclimatic events underpin phylogeographic patterns of marine macroalgae in the Northwest Pacific.

The Northwest Pacific (NWP) harbors one of the world's most exceptional marine macroalgal biodiversity hotspots. Recurrent Quaternary glacial-interglacial cycles and a unique mosaic of semi-enclosed marginal seas with complex oceanographic dynamics have fundamentally shaped the genetic differentiation and biogeographic distribution of coastal macroalgal populations across the region. However, existing phylogeographic studies are fragmented and inconsistent, lacking a unified mechanistic framework to resolve how species-specific life-history traits and modern oceanographic conditions modulate historical evolutionary signatures, leaving key interspecific pattern conflicts unresolved. Therefore, this review synthesizes empirical evidence across taxa and regions to construct a unified conceptual model integrating paleoclimatic isolation, post-glacial recolonization, barrier-mediated differentiation, and current-driven asymmetric gene flow. We clarify interspecific conflicts through a trait-based lens and assess how accelerating climate change disrupts millennial-scale evolutionary patterns. We further identify critical methodological limitations, including low marker resolution and underutilization of genomic approaches, that constrain current inferences and motivate priority research directions such as population genomics, paleodistribution modeling, and expanded sampling of underrepresented taxa. This synthesis advances a predictive evolutionary paradigm to guide targeted conservation of genetic diversity and climate-resilient macroalgal habitats across the Northwest Pacific.