Environmental monitoring is essential to assess and, if possible, anticipate the consequences of various marine economic developments. This study describes progress in environmental monitoring by developing and applying a eutrophication index (EI) for marine protected areas (MPAs). The EI combines available data, such as biological oxygen demands, dissolved inorganic nitrogen and phosphorus, and chlorophyll-a, with the weighting factors calculated from principal component analysis to assess environmental quality. Its effectiveness was tested using nearly three decades of environmental data (since 1996) from the Nha Trang MPA in Vietnam. The EI revealed clear trends in environmental quality. In the period 1996–2006, environmental conditions deteriorated, negatively impacting aquaculture. In the later period, 2007–2024, improved environmental protection policies, technological developments, expanding tourism, and heightened public awareness contributed to a reversal of this trend. During the earlier period, the EI indicated poor environmental quality (Level V), while in the later years, it improved significantly, approaching Level II. This study also identified the spatial eutrophication patterns and helped to determine the causes of specific eutrophication levels. These included port development, aquaculture activities, and domestic waste discharge. These findings highlight the close relationship between environmental quality and economic activities in the bay. Overall, the new EI and its sensitivity maps enhance environmental monitoring capabilities. They provide valuable tools for decision-makers, aiding in the strategic planning of marine economic development, ecosystem protection, and sustainable resource use. The approach supports long-term environmental stewardship and more informed, adaptive management of coastal and marine areas.

As sessile marine organisms, soft corals may use chemical or/and physical factors of defense against fish predators for their survival and growth. In Vietnam, corals of the speciose genus Sarcophyton are abundant on reefs. However, little is known about their defensive traits and strategies. In the study of feeding deterrence, experiments in the field and in an aquarium were conducted using only crude extract, only sclerites, and a mixture of both from Sarcophyton cinereum, S. glaucum, S. serenei, S. trocheliophorum and Sarcophyton sp. For all species, pellets containing a mixture of crude extract and sclerites were consumed by reef fishes from 0.8 to 14.6% (in the field, F) and from 0.3 to 13.3% (in aquarium, A); crude extract was consumed from 5.2 to 42.6% (F) and from 7.4 to 64.0% (A); and sclerites were consumed from 34.6 to 100% (F) and from 30 to 83.3% (A). The consumption of pellets containing S. serenei sclerites was significantly reduced both in the field assays with reef fishes and in the aquarium assays with the moon wrasse Thalassoma lunare (P < 0.05), which showed sclerites as a dominant physical factor in the S. serenei feeding deterrence. Overall, in Sarcophyton soft corals, the effect of fish predation prevention was most pronounced in the combination of both chemical and physical defense factors, followed by the chemical and then the physical factor alone. Hence, both chemical and physical factors of defense against predation may contribute to the Sarcophyton abundance on reefs.

Bacteria associated with invertebrates are considered as good sources for biologically active compounds. Sponge-derived bacteria were screened for antimicrobial activities, the presence of the cluster genes of polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs), and through a colony picking method. Crude extracts of broth cultures were tested for microbial inhibition. Eleven out of 25 isolated strains showed inhibition of at least one of eight tested indicator microorganisms. Antimicrobial activities were observed in the strains coded HM5, HM6, and HM9 with the presence of NRPS and PKSII genes, whereas the isolate HM21 held both NRPS and PKSII and inhibited only the growth of Bacillus subtilis by the well diffusion method and only inhibited Serratia marcescens by the colony picking method. Two isolates, HM5 and HM6, belonged to the species of Bacillus. Interestingly, the isolate HM9 was nearest to Streptomyces mexicanus^T NBRC100915 (GenBank accession number AB249966) with 94% sequence similarity. This potent strain HM9 could possibly be considered as a new species and a good source for bioactive compound discovery. Some isolates showed NRPS/PKS genes but did not exhibit antimicrobial activity. Thus, we suggested that both molecular and traditional methods should be conducted for the screening of antimicrobial producers.

Xeniidae is a soft coral family that has contributed to the diversity of tropical coral reef communities, including those found in Southeast Asia. From 50 soft coral samples of the family Xeniidae collected from coastal fringing reefs along the coast of central Vietnam, five species have been recorded belonging to two genera, Xenia (two species) and Heteroxenia (three species). Of five species, two were recorded for the first time in Vietnam are Xenia novaebritaniae Ashworth, 1900 and Heteroxenia elisabethae Kölliker, 1874. An identification key was provided based on colony forms and morphological characters of sclerites for five xeniid corals in Vietnam.

The distribution of critical marine habitats in Quy Nhon Bay, Binh Dinh Province, was assessed with the combination of resolution of Google Earth images and local knowledge through local consultations and ground truthing using small boats to check the sites supporting coral reefs and seagrass beds with local involvement. Detailed surveys on species diversity and conditions of marine habitats were conducted at 24 sites of coral reefs and four sites of seagrass beds at three sites (Nhon Ly, Nhon Hai, Ghenh Rang, and Nhon Chau) in 2016–2017. More than 152 ha of coral reefs, 5 ha of seagrass beds, and 720 species belonging to 7 key groups (290 species of fishes; reef-building corals: 194, molluscs: 123, seaweeds: 47, echinoderms: 40, crustaceans: 20 and seagrasses: 6 species) associated with the above habitats were recorded in the Bay. Among them, 92 species were facing different threats, in which 3 species were endangered (EN), including branching corals (Alveopora minuta), flat pen shells (Atrina vexillum), and top shells (Tectus pyramis); 38 species at vulnerable (VU); and 51 species at near threatened (NT) following the IUCN Red List and Vietnam Red Book. In general, the coral reefs and seagrass beds at Bai Dua and Seo Island (Nhon Ly); Kho Nho Island, Bo Dap (Nhon Hai); S. Ngang Island, Bai Nam and Bai Nom of Dat Island (Ghenh Rang); Da Ban, Bai Lang, Bai Lang Ba and Ong Gia Island (Nhon Chau) supported higher diversity and better conditions than other sites. Establishing restricted zones at these sites is an urgent need, but it also holds the premise of sustainable utilization and conservation of resources in the future.