Current advances in seagrass research: A review from Viet Nam

Abstract

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total C _org stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity.

Keywords: degradation; distribution; diversity; ecosystem services; seagrass; taxonomy.

Figure 1

Seagrass distribution in Viet Nam. The four different color cycles indicate seagrass distribution in four different regions. Data were combined from various studies. See Table 1 for more details.

Figure 2

Changes of seagrass beds at three sites of Van Phong Bay (region 3) from 1998 to 2018 deduced by using datasets of satellite image Landsat 5 TM and Landsat 8 OLI. The figure was adapted from Vo et al. (2020).

Figure 3

Phylogeny of members of the genus Halophila 612 bp of the ITS1-5.8S-ITS2 sequence. Leaf morphology of Halophila spp. from samples collected in Viet Nam were placed beside the phylogenetic tree. Scale in each leaf figure = 1 mm. The figure was modified from Nguyen et al. (2021a).

Figure 4

The cluster analysis of the Thalassia hemprichii population from southern Viet Nam based on nine microsatellite loci. Eight populations were divided into two groups consisting of the open sea and lagoon clusters. Adapted from Nguyen et al. (2022).

Figure 5

Distribution of haplotype frequency of Halophila major. Twenty-two haplotypes were found from dataset of 69 ITS sequences of H. major collected in five geographic regions: Sunda Shelf (I), Wallacea (II), Sahul Shelf (III), Bay of Bengal (IV), and coast of Japan (V). Source: Nguyen et al. (2021b).