Genetic Diversity and Connectivity of Reef-Building <em>Halimeda macroloba</em> in the Indo-Pacific Region

Understanding the population genetic connectivity is crucial for the sustainability and persistence of marine biodiversity. As fundamental reef-building macroalga in the coastal ecosystem, Halimeda macroloba is one of dominant intertidal seaweed in the Indo-Pacific region. However, the genetic structure and population connectivity haven&rsquo;t been recog-nized yet. Here, we explored the population genetic structure and genetic connectivity of H. macroloba using chloroplast tufA, rps3-rpl14 and rbcL. Our results indicated low genetic diversity and shallow population genetic structure at the intraspecific level, uncovering 3 genetic groups with 5 subdivided lineages in tufA and 2 genetic clusters in rps3-rpl14. We detected demographic expansion in the last glacial period of Pleistocene and significantly asymmetric gene flow among different geographical units. We suggested that the south-westward ocean currents under the influence of northeast monsoon in the Indo-Pacific re-gion was the main reason for shaping the present genetic structure; and the asexual re-production of H. macroloba also played an important role of the low genetic diversity pat-tern; as well, the divergence between genetic clusters might be related to the historical iso-lation led by the paleoclimate oscillation in Pleistocene. The Xisha islands in southern China might serve as a potential refugium of H. macroloba, which needs extra attention to the conservation management. Given the limitation of sample size, we&rsquo;ll conduct more field work and carry out further research at larger scale in the future. Our study shed light into the theory of population connectivity in the Indo-Pacific region, and provided scien-tific basis for the tropical costal seaweed conservation.