Island populations have less genetic variation, but are more genetically isolated than mainland populations in anecosystem engineer, seagrass (<i>Zostera marina</i>) in South Korea: conservation implications for future management
Creators: name: Lee, Hyuk Je
name: Byeon, Seo Yeon
name: Kim, Jae Hwan
name: Kang, Ji Hyoun
name: Jang, Ji Eun
name: Choi, Sun Kyeong
name: Kim, Min Ji
name: Park, Sang Rul
Publisher: name: F1000Research
Year: 2017

description: Seagrasses, marine angiosperms, provide numerous ecosystem services for coastal and estuarine environments. They are often called ‘ecosystem engineer’ as they can modify surrounding marine environments, creating their own habitats. <i>Zostera marine</i> (common name ‘eelgrass’) is one of the seagrass bed-forming species distributed widely in the northern hemisphere including the Korean Peninsula. Recently, however, there has been a drastic decline in the population size of <i>Z. marina </i>worldwide including Korea, primarily due to anthropogenic pressure such as climate change and habitat destruction. Although an understanding of the extent of intraspecific genetic diversity and genetic structure of ‘natural’ populations is a key factor in the ultimate success of conservation efforts, little attention has been paid to the population genetic structure of eelgrass populations in South Korea. In the present study, to our knowledge, we are the first to assess the current population genetics status of this species on the entire coasts of South Korea (Jeju Island, South Sea, East Sea and West Sea) in addition to the East China Sea by estimating the levels of genetic diversity and genetic structure using eight microsatellite markers. Eight-hundred-forty specimens were collected from 24 geographic localities in the South Sea (6 populations), East Sea (6), West Sea (4) and Jeju Island (5), which is located approximately 155 km off the southernmost region of the mainland and also in the East China Sea (3).<br><br>Populations from Jeju Island displayed a much higher rate of asexual reproduction, as indicated by a lower level of clonal diversity and thus significantly lower genetic diversity (allelic richness) compared to other coastal regions. However, Jeju Island populations showed significantly higher levels of inter-population differentiation (<i>F</i><sub>ST</sub>) than any other regions (p &lt; 0.05), although they are geographically more closely located one another (0.6-26.4 km). Overall, South Korean eelgrass populations were all strongly genetically divergent from one another, suggesting that limited contemporary gene flow has been occurring among populations. Results of FCA (factorial correspondence analysis) suggest that Z.marina populations analyzed here are most likely to form four distinct genetic clusters including Jeju Island, South/West Sea, East Sea and East China Sea. However, a Baysian population assignment test with STURCURE revealed that the most likely number of genetic clusters after Delta K Evanno's correction corresponds to K=7. Microsatellite-based phylogenetic analysis with a Neighbor Joining (NJ) method, indicates that Jeju Island populations are most distantly related, and the South and West Sea populations are most closely related. Small effective population sizes (Ne) and limited population connectivity, particularly for populations in Jeju Island indicate that these island populations may be vulnerable to local extinction under changing environment, especially given that Jeju Island is one of the fastest warming regions around the world. Overall, our work will inform on conservation and restoration efforts, including transplantation for eelgrass populations at the southern tip of Korea for this ecologically important species. To this end, we here suggest that populations from the South Sea can be used as source material through transplantation for the restoration of island populations, given the elevated levels of genetic diversity and also their close evolutionary relationships.