Update of seagrass cover and species diversity in Southern Viet Nam using remote sensing data and molecular analyses

Along with coral reefs and mangroves, seagrass meadows are being threatened globally Southeast Asia is considered within the area of seagrasses’ cradle of diversity. However, information on the current status of seagrass beds from Southern Viet Nam is limited due to lack of reliable data about seagrass species occurring in the Southeast Asian region. One factor is the difficulty of unambiguous species identification. For example, the leaf morphological characteristics of Halophila ovalis and closely related species are overlapping which leads to misidentifications. In this study, the latest satellite Landsat 8 OLI and SENTINEL-2B image analyses were applied to determine the distribution of seagrass beds in Southern Viet Nam. Detailed morphological and genetic marker analyses were used to determine and update the species composition. The present study together with literature reviews indicate that the total area of seagrass beds from Southern Viet Nam are 10,832.1 ha. 2562 ha (or 19.1%) of seagrass coverage has been lost. The seagrass beds at Phu Quoc Island are the largest with 7579 ha. The occurrence of Halophila major is updated for almost all off-shore islands and open-water areas. •The total area of seagrass beds from Southern Viet Nam is estimated about 10,832.1 ha.•Halophila ovalis occurred mainly in the lagoon.•H. major was found almost around off-shore islands and in open-water areas.•rDNA marker analysis revealed putative hybridizations between Halophila spp.•H. minor should be also listed on the IUCN Red List of threatened seagrass species.