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For 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. [ABSTRACT FROM AUTHOR]

Genetic diversity and distribution patterns of marine macroalgae are increasingly being documented in Southeast Asia. These studies show that there can be significant levels of genetic diversity and isolation between populations on either side of the Thai-Malay Peninsula. Bostrychia tenellla is a common filamentous red seaweed in the region and the entity is represented by at least two cryptic species. Despite being highly diverse and widespread, genetic variation and population structure of this species complex remains understudied, especially around the Thai-Malay Peninsula. We analyzed genetic diversity and inferred the phylogeographic pattern of specimens identified as B. tenella using the plastid RuBisCo spacer from samples from the Andaman Sea and the Gulf of Thailand. Our genetic analysis confirmed the occurrence of the two cryptic B. tenella species (B and C) along both coasts. Cryptic species B was more common in the area and displayed higher genetic diversity than species C. Historical demographic analyses indicated a stable population for species B, but more recent population expansion for species C. Our analyses also revealed that both cryptic species from the Andaman Sea possessed higher genetic diversity than those of the Gulf of Thailand. We also detected moderate to high levels of gene flow and weak phylogeographic structure of cryptic species B between the two coasts. In contrast, phylogeographic analysis showed genetic differences between populations of both cryptic species within the Andaman Sea. Overall, these results suggest that cryptic B. tenella species around Thai-Malay Peninsula may have undergone different demography histories, and their patterns of genetic diversity and phylogeography were likely caused by geological history and regional sea surface current circulation in the area. [ABSTRACT FROM AUTHOR]