Marine conditions in Andaman Sea shape the unique genetic structure of Sargassum plagiophyllum C. Agardh

The Andaman Sea-Malacca Strait is an area with high maritime complexity and rich seaweed biodiversity. The brown seaweed Sargassum plagiophyllum C.Agardh occurs abundantly in the intertidal in the area. However, its population genetics has not been studied. Here, we used the nuclear Internal Transcribed Spacer 2 of the ribosomal cistron ITS2 and the mitochondrial cytochrome c oxidase subunit 1 gene cox1 as genetic markers to determine the population genetic structure along the entire west coast of Thailand. A total of 351 individuals from the ten populations were genotyped. Nine different cox1 haplotypes and 17 different ITS2 ribotypes were found. Generally, S. plagiophyllum populations were found to have low genetic diversity. Two lineages were found based on ITS2 and two cryptic diversities were inferred from cox1 data. Most individuals belonged to the one single ribotype and haplotype. Ocean currents are believed to influence the S. plagiophyllum distributions and connectivity between populations. Higher phosphate concentrations during the northeast monsoon season could promote its growth and propagation. Our study suggested that the temporal and spatial transformation of the marine environment in the Andaman Sea influences the distribution, biomass, and population genetic structure of S. plagiophyllum, our results are beneficial for the management of seaweed resources.