Part of the Indo-Chinese peninsula and located on the northwest edge of the Coral Triangle in the South China Sea, the Vietnamese coastal zone is home to a wealthy marine biodiversity associated with the regional geological setting and history, which supports a large number of marine ecosystems along a subtropical to tropical gradient. The diversity of coastal benthic marine primary producers is also a key biological factor supporting marine biological diversity. The present review provides: (1) an updated checklist of the Vietnamese marine flora, (2) a review of molecular-assisted alpha taxonomic efforts, (3) an analysis of marine floral biodiversity spatial distribution nationally and regionally (South China Sea), (4) a review of the impact of anthropogenic and environmental stressors on the Vietnamese marine flora, and (5) the efforts developed in the last decade for its conservation. Based on the studies conducted since 2013 and the nomenclatural changes that occurred during this period, an updated checklist of benthic marine algae and seagrasses consisted in a new total of 878 species, including 439 Rhodophyta, 156 Ochrophyta, 196 Chlorophyta, 87 Cyanobacteria, and 15 phanerogam seagrasses. This update contains 54 new records and 5 new species of macroalgae. The fairly poor number of new records and new species identified in the last 10 years in a “mega-diverse” country can be largely attributed to the limited efforts in exploring algal biodiversity and the limited use of genetic tools, with only 25.4% (15 species) of these new records and species made based on molecular-assisted alpha taxonomy. The South Central Coast supports the highest species diversity of marine algae, which coincides with the largest density of coral reefs along the Vietnamese coast. Vietnam holds in the South China Sea one of the richest marine floras, imputable to the country’s geographical, geological, and climatic settings. However, Vietnam marine floral biodiversity is under critical threats examined here, and current efforts are insufficient for its conservation. A methodical molecular-assisted re-examination of Vietnam marine floral biodiversity is urgently needed, complemented with in-depth investigations of the main threats targeting marine flora and vulnerable taxa, and finally, conservation measures should be urgently implemented.

Phthalic acid esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs) are known to potentially impact both marine organisms and human health through the consumption of fish and seafood. In this study, the concentrations of 12 priority PAHs and 6 PAEs were analyzed in the tissues of 76 samples of five farmed fish species, including Litopenaeus vannamei (crustacean), Babylonia areolata, Marcia hiantina (mollusk), Trachinotus blochii, and Epinephelus lanceolatus (fish), collected from four coastal sites in Khanh Hoa province. Freeze-dried tissue was extracted using water bath ultrasonication with an acetone/n-hexane mixture. A triple quadrupole gas chromatograph–mass spectrometer (GC-MS/MS) was used for the analyses. The results showed that the total PAHs had low contamination levels. Among the PAEs, bis(2-ethylhexyl) phthalate (DEHP) exhibited the highest concentrations. The calculated hazard index (HI) for PAEs suggested no significant health risk. Six PAHs were detected, ranging from 9.14 µg kg⁻¹ in Pacific white shrimp to 47.34 µg kg⁻¹ in cockle. The incremental lifetime cancer risk (ILCR) values for PAHs in some samples exceeded the acceptable safety threshold. In the future, natural fish, environmental samples (seawater and marine sediment), and other information on natural conditions will be collected for analyses. This is the first report on the levels and health risks of PAEs and PAHs in farmed fishes along the Khanh Hoa coast.

On 5 November 2020, a poisoning event involving four people by the consumption of moray eel occurred in Khanh Hoa Province, Viet Nam, with signs indicative of ciguatera. The remaining moray portion was confiscated for identification of causative species and responsible toxins. The phylogenetic study based on COX1 identified the moray as Gymnothorax javanicus Bleeker (1859). Out of 17 marine lipophilic toxins (MLPs) that were analyzed using LC-MS/MS, only Pacific ciguatoxin-1 (P-CTX-1) was detected in the moray’s flesh at 1.30 ± 0.004 ng/g ww, while no toxin was found in the skin. The N2a assay’s ciguatoxicities in the skin and flesh were 0.69 ± 0.075 and 2.49 ± 0.216 ng P-CTX-1/g ww equivalent, respectively. In the N2a assay, the P-CTX-1 amount in the moray flesh was 1.9 times greater than that determined by LC-MS/MS, indicating the presence of additional sodium channel activators or a matrix effect. The P-CTX-1 amount in the moray flesh was at a level that generates major ciguatera poisoning (CP) symptoms in humans (1.0 ng/g P-CTX-1), makes sense given that four consumers experienced the onset of poisoning symptoms. This study is significant for the management of seafood safety since it is the first scientific report on the species and toxin in a moray causing ciguatera in Viet Nam.

This study presents a new flattened species of Meristotheca collected from southern Viet Nam. Meristotheca lysonensis sp. nov. is proposed based upon several morphological characters and genetic differences when compared to the closely related species documented in Southeast Asia: M. procumbens. This new species shows larger size and blade thickness, as well as both basal and lateral pit-connections between tetrasporangia and the parental supporting cells. The phylogenetic analyses also support Meristotheca lysonensis as a new species.

Contamination by heavy metals in coastal and marine environments is an increasingly serious threat to both marine ecosystems and humans. The numerous marine cultivation and industrial zones along the coast of Khanh Hoa may influence the heavy metal contamination in the seawater and marine sediments. In this study, 36 seawater and 36 marine sediment samples were collected along the coast of Khanh Hoa to evaluate the levels of eight heavy metal elements. The results indicated that heavy metal concentrations in the surface seawater at Khanh Hoa were much lower than the national technical regulatory limits. The comprehensive pollution index of the heavy metals averaged less than 1. Therefore, heavy metal pollution in the seawater along the coast of Khanh Hoa is slight. Among the eight heavy metals (Cd, Co, Cu, Cr, Mn, Ni, Pb, and Zn) analyzed in the sediments, Cu concentration in the sediment at Cam Ranh Bay is much higher than the national technical regulatory limit. Ecological risk assessment of the sediments also indicated a possible combined biological effect of Cu, Pb, and Zn at Cam Ranh. Therefore, heavy metals in the marine environment at Khanh Hoa should be monitored yearly. Decision-makers should consider the Cu content in seafood because bioaccumulation of heavy metals may occur in marine organisms.