Characteristics of the seagrass meadows in Ba Hon Dam Islands, Ba Lua Archipelago, Vietnam

This study aimed to assess the species diversity, distribution, and biomass of seagrass meadows in Ba Hon Dam, Ba Lua Archipelago, Vietnam. Through two surveys conducted in June 2022 and March 2023, using snorkeling and transect surveys in the subtidal zone, four seagrass species were recorded: Thalassia hemprichii, Oceana serrulata, Halodule uninervis, and Enhalus acoroides. The study also documented their morphological characteristics. With a seagrass meadow area of approximately 9 hectares, the average coverage was 83% in June 2022 and 71% in March 2023. Enhalus acoroides and Thalassia hemprichii were dominant in both coverage and biomass, often forming dense seagrass meadows in Ba Hon Dam. The species Enhalus acoroides exhibited the longest average leaf length of 63.62 ± 1.82 cm and the tallest average plant height of 76.71 ± 3.45 cm during the 6/2022 survey. Due to its large size, Enhalus acoroides had the lowest shoot density, averaging 52.00 ± 23.75 shoots/m² recorded in March 2023, while Thalassia hemprichii had the highest shoot density at 427.22 ± 132.60 shoots/m² recorded in June 2022. The average dried biomass density for all seagrass species found at Ba Hon Dam meadows was 920.46 g/m2 in 6/2022 and 790.24 g/m2 in 3/2023, respectively. The biomass density of Thalassia hemprichii in Ba Hon Dam was higher than that recorded in the Hai Tac Archipelago but lower than that recorded in Nam Yet Island. The research results have contributed the first data on seagrass meadows in the Ba Hon Dam area to the overall database of seagrass biodiversity in the West Sea of Vietnam.