High-value sea cucumber species are overexploited, and the focus of fishing has shifted to low-value species, e.g., Holothuria (Halodeima) atra. In this study, the population of H. atra was investigated in three different habitats: a seagrass habitat, a seaweed habitat, and bare sand, at an intertidal zone of Lidee Island, Mu Ko Phetra National Park, Satun Province, Thailand. The habitat type was the predictor which had a significant impact on the density and frequency distribution of the body length of H. atra individuals. H. atra was only found in the seaweed and seagrass habitats. The highest density of this species, 91.1 ± 9.6 inds 100 m⁻², was found in the seaweed habitat. The frequency distribution of the body length of H. atra individuals in the seagrass habitat showed no significant change throughout the study period, but the mode of the length frequency distribution in the seaweed habitat gradually rose from 9 to 22 cm from January−September 2019. Asexual reproduction was the major source of recruitment. The occurrence of recently fissioned individuals was slightly higher in the seaweed habitat than in the seagrass habitat (6.0 ± 1.1% and 2.2 ± 0.6%, respectively). This study showed that H. atra was most abundant in the seaweed habitat, which is likely because of the greater availability in this habitat of food sources, microhabitats, and protection against sun irradiance, desiccation, and stress during low tides.

The Mekong Delta is one of the largest deltas in the world, spanning approximately 55,000 km2 and sharing approximately 50.2% of Vietnam’s mangrove ecosystems (90.8 km2 km2; Tinh et al., 2022). Supporting ~18 million people, the Mekong Delta region faces many pressures, including land conversion for shrimp aquaculture, expanding urban centres, deforestation, and coastal erosion. In response to these challenges, mangrove forests in the Mekong Delta have been the focus of several restoration and conservation efforts in recent years, with 27.3 km2 of coastal mangrove forests currently being restored and/or conserved under current forest management efforts.The purpose of this study is to quantify how mangrove restoration in Ca Mau province, Viet Nam, delivers blue carbon additionality within mangrove ecosystems, particularly where land conversion for shrimp aquaculture has driven deforestation. Field sampling for total ecosystem carbon stocks across natural and restored forests, including integrated shrimp-mangrove aquaculture systems, reflecting one of the region's dominant land-use practices, was carried out by using standardized blue carbon protocols. Mangrove tree diameter, height and species, and downed dead wood were measured and recorded to estimate biomass and necromass carbon stocks. 397 soil samples were collected to estimate belowground soil carbon stocks. Preliminary results from two natural and two restored sites of different ages, show clear evidence of additionality in both aboveground and belowground carbon stores after restoration. However, a comparison of earth observation data between 2010 and 2024 allows us to provide a tentative estimate of carbon losses due to ongoing coastal erosion in these fringing mangrove forests.These results highlight that efforts to restore mangrove forests in the Mekong Delta can deliver quantifiable blue carbon benefits, potentially underpinning new carbon crediting opportunities to help fund further mangrove restoration across the Mekong Delta. For restoration efforts to be effective in the long-term, careful consideration of ongoing habitat loss, increasingly driven by coastal erosion in response to anthropogenic sea-level rise, will be necessary.