Viet Nam

Viet Nam is a nation in Southeast Asia. It borders the People’s Republic of China to the north, Laos to the northwest and Cambodia to the southwest. To the country’s east lies the South China Sea. With a population of approximately 84 million, Viet Nam is one of the most densely populated nations in Southeast Asia.

The earliest record of seagrass in Viet Nam was in 1885 when Balansa discovered Halophila ovalis and H. beccarii in the Song Hong Meo River (now part of the Ruot Lon River) near Quang Yen District, Quang Ninh Province (Van Tien 2008).

There are 14 species of seagrass reported in Viet Nam (Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule pinifolia, Halodule uninervis, Halophila beccarii, Halophila decipiens, Halophila minor, Halophila ovalis, Ruppia maritima, Syringodium isoetifolium, Thalassia hemprichii, Thalassodendron ciliatum and Zostera japonica).

Viet Nam is at the overlap of temperate and tropical seagrass species with Zostera japonica growing intertidally in the north and mixing with Halophila ovalis, while in the south the species composition is similar to the Philippines and Malaysia. Ruppia maritima is common in coastal zones in northern Viet Nam, Halophila ovalis is widespread in coastal zones and around islands in north and central Viet Nam, and Halodule pinifolia is particularly prevalent in southern areas of Viet Nam.

The total area of seagrass in Viet Nam is estimated at 17,675ha (Van Tien, Pers. Comm. 23 Mar10). Seagrass medaows are distrubuted along the entile coastline with meadows occurring from Viet Nam’s northern border with China, through to the south-western border with Cambodia, but mostly from the middle of the southern sections. Their status is unknown though in general the Vietnam coastal zone has been heavily impacted by sedimentation and domestic and agricultural pollution.

Seagrass meadows in Viet Nam have suffered serious degradation, with approximately 45 to 50% of their areas lost over the past 2 decades. Threats to seagrasses in Viet Nam include both natural and human induced. Natural threats in include typhoons (Tonkin Gulf in northern Viet Nam experiences an annual average 35 typhoons), turbidity and sedimentation (river runoff from agriculture, foresty, and urban development) and freshwater runoff (particularly during the rainy season). Human-induced threats include destructive fishing methods (eg explosives, trawling, gill net, drift net, bottom net, blanket nets, fine square nets, electro-fishing, cyanide trampling, gleaning, and digging), aquaculture (construction of ponds on tidal flats), coastal construction (eg roads, bridges, houses, ports and dredging), pollution (eg wastewater discharges composed of heavy metals, suspended sediments, nutrients, and oils), and reclamation of tidal flats for agricultural purposes. The main causes of seagrass degradation stem from low awareness and unstable economic conditions.

Seagrasses in Viet Nam are important either for direct use or as habitat. The majority of exploited seagrasses (particularly Zostera and Ruppia) are used as feed for livestock and fertiliser. The main importance of seagrass is however as the use of associated biota, such as algae (eg Gracilaria spp of commercial value), harvesting of the swimming crabs (Portunus pelagicus and P. sanguinolentus), sea cucumbers (commercially important species Holothuria scabra and Halodeima atra), fin fish (at least 34 commercially important species), and seahorses (in particular Hippocampus kuda). Seagrass in Viet Nam is also important as food for dugongs (Dugong dugon) and green turtles (Chelonia mydas).

Until recently, it was widely considered that the only remaining population of dugongs in Viet Nam inhabited areas of Con Dao National Park, an archipelago of 14 islands in the southern province of Ba Ria-Vung Tau. The major threats to dugongs in Viet Nam are hunting (not widespread), gill nets and starvation through habitat destruction.

Seagrass monitoring in Viet Nam is also conducted are part of the UNEP/GEF project reversing environmental degradtion trends in the South China Sea and Gulf of Thailand (www.unepscs.org).

For more detailed information on seagrasses in Viet Nam, see Van Tien (2008)