Contrasting patterns of genetic diversity and population discontinuity in the common red seaweed Gracilaria salicornia (Gracilariaceae) along the coasts of Thailand

ABSTRACTFor long-term management and conservation of marine resources an understanding of their genetic diversity and geographic distribution is necessary. The red alga Gracilaria salicornia is widely distributed along the coasts of Thailand and has been used as food and as fertilizer. However, there have been no studies examining the genetic diversity of this alga. The present research aimed to employ two different genetic markers, mitochondrial (COI-5P) and chloroplast (RuBisCO spacer) for exploring the genetic diversity and phylogeography of G. salicornia in Thailand. Our analyses, inferred from both markers, revealed different levels of genetic diversity between the two coasts of Thailand, and the recognition of seven new COI haplotypes. Gracilaria salicornia in the Andaman Sea had higher genetic diversity than in the Gulf of Thailand. Significant genetic divergence was found between populations in the Andaman Sea and the Gulf of Thailand, likely due to the geographic barrier of the Thai-Malay Peninsula and the complex ocean currents. No genetic structuring was detected in the Gulf of Thailand, whereas low to moderate genetic differentiation was found between populations in the Andaman Sea, suggesting a possible break between the northern and southern Andaman Sea. This break could be explained by ocean circulation patterns around the Malacca Strait. These findings provide further evidence supporting the Thai-Malay Peninsula and oceanographic currents as strong barriers to dispersal, leading to genetic differentiation and population structuring of G. salicornia and other marine species. These results can be used to guide conservation management actions and exploitation of this marine resource.KEYWORDS: COIMacroalgaePopulation geneticsPhylogeographyRhodophyta ACKNOWLEDGEMENTSWe thank Jantana Praiboon and Jakaphan Bulan for help collecting and sequencing samples. We also thank the associate editor Gavin Maneveldt and two anonymous reviewers for their comments and suggestions.DISCLOSURE STATEMENTNo potential conflict of interest was reported by the authors.Supplementary InformationSupplemental data for this article can be accessed online at https://doi.org/10.1080/00318884.2023.2254621Additional informationFundingThis work was supported by a research grant to NM from the Thailand Research Fund (MRG6080040).