AFLP analysis revealed a north to south genetic break in the brown alga Sargassum thunbergii along the coast of China

Sargassum thunbergii, a common brown macroalga that occurs in the Asian Northwest Pacific, has important ecological services and economic values. In recent years, the distribution range and biomass of wild S. thunbergii resources have declined rapidly due to severe anthropogenic impacts and habitat loss. To slow the decline of this natural resource by taking appropriate measures, it is very important to evaluate the population genetic structure and diversity of S. thunbergii. In this study, we used amplified fragment length polymorphism (AFLP) markers to investigate population genetic differentiation and diversity of S. thunbergii along the coast of China at a genome-scanning scale. Five primer combinations that yielded high polymorphisms were identified in ten populations of S. thunbergii. Genetic analyses revealed low genetic diversity within populations and high levels of genetic differentiation among populations. Moreover, apparent gene flow occurred between S. thunbergii populations in the Yellow-Bohai Sea, whereas no such exchange was detected in the populations of the East China Sea. Genetic clustering, principal coordinates analysis (PCoA), and pairwise FST estimates consistently indicated that S. thunbergii populations divided into two genetic groups, coinciding with their geographical distribution (Yellow-Bohai Sea vs. East China Sea). The detected genetic diversity of S. thunbergii along the coast of China provides important insights not only for selecting high-yielding varieties for commercial cultivation, but also for proposing strategic management plans to protect and restore declining natural resources under anthropogenic climate change.