Population genetic structure of the exotic smooth cordgrass Spartina alterniflora and its invasion into Korean coasts

Abstract The smooth cordgrass, Spartina alterniflora Loisel, is an aggressive invasive species that causes a significant negative impact on coastal ecosystems worldwide. The species is native to the eastern United States, but has spread rapidly along East Asian coasts and was unintentionally introduced into Korea, leading to the devastation of native ecosystems. Here, we examined the population genetic structure and invasion pathway of S. alterniflora along Korean coasts using chloroplast DNA (cpDNA). Our results revealed that the S. alterniflora population in Korea has a strong genetic structure, primarily consisting of two geographically isolated haplotypes (C1 and C4). Furthermore, two individuals were found to have haplotype N, which might be a newly discovered haplotype in this study. The haplotypes C1 and C4 are widely distributed in the native population as well as in the introduced population in East Asia. Thus, the presence of these two haplotypes in different localities in Korea suggests multiple invasion events. Comparisons of the cpDNA data of this study with the available GenBank data from the native range in the U.S. and the invasive range in East Asia (China and Japan) revealed that the East Asian population (China, Japan, and Korea) is nearly homogeneous (AMOVA; Fst = 0.06871, p = 0.5) with no restricted gene flow. Our study suggests that the C1 and C4 haplotypes might have been introduced into Korea multiple times particularly from China, possibly via natural dispersal or transport vectors. These emphasize the importance of strengthening coastal management to prevent further spread.