[1] Harmful algal blooms (HABs) in the southeastern Vietnamese coastal waters have caused large economic losses in aquacultured and wild fisheries in recent years; however, there have been few oceanographic studies on these HAB events. The present study reports an extensive HAB off southeastern Vietnamese waters during late June to July 2002 with in situ observations and analyzes the oceanographic conditions using satellite remote sensing data. The HAB had high chlorophyll a (Chl a) concentrations (up to 4.5 mg m À3 ) occurring $200 km off the coast and $200 km northeast of the Mekong River mouth for a period of $6 weeks. The bloom was dominated by the harmful algae haptophyte Phaeocystis cf. globosa and caused a very significant mortality of aquacultured fish and other marine life. In the same period, sea surface temperature (SST) imagery showed a cold water plume extending from the coast to the open sea, and QuikScat data showed strong southwesterly winds blowing parallel to the coastline. This study indicated that the HAB was induced and supported by offshore upwelling that brings nutrients from the deep ocean to the surface and from coastal water to offshore water and that the upwelling was driven by strong wind through Ekman transport when winds were parallel to the coastline. This study demonstrated the possibility of utilizing a combination of satellite data of Chl a, SST, and wind velocity together with coastal bathymetric information and in situ observations to give a better understanding of the biological oceanography of HABs. INDEX TERMS: 4855

Viruses attract increasing interest from environmental microbiologists seeking to understand their function and role in coral health. However, little is known about their main ecological traits within the coral holobiont. In this study, a quantitative and qualitative characterization of viral and bacterial communities was conducted on the mucus of seven different coral species of the Van Phong Bay (Vietnam). On average, the concentrations of viruses and bacteria were, respectively, 17- and twofold higher in the mucus than in the surrounding water. The examination of bacterial community composition also showed remarkable differences between mucus and water samples. The percentage of active respiring cells was nearly threefold higher in mucus (m = 24.8%) than in water (m = 8.6%). Interestingly, a positive and highly significant correlation was observed between the proportion of active cells and viral abundance in the mucus, suggesting that the metabolism of the bacterial associates is probably a strong determinant of the distribution of viruses within the coral holobiont. Overall, coral mucus, given its unique physicochemical characteristics and sticking properties, can be regarded as a highly selective biotope for abundant, diversified and specialized symbiotic microbial and viral organisms.

There is increasing suspicion that viral communities play a pivotal role in maintaining coral health, yet their main ecological traits still remain poorly characterized. In this study, we examined the seasonal distribution and reproduction pathways of viruses inhabiting the mucus of the scleractinians Fungia repanda and Acropora formosa collected in Nha Trang Bay (Vietnam) during an 11-month survey. The strong coupling between epibiotic viral and bacterial abundance suggested that phages are dominant among coral-associated viral communities. Mucosal viruses also exhibited significant differences in their main features between the two coral species and were also remarkably contrasted with their planktonic counterparts. For example, their abundance (inferred from epifluorescence counts), lytic production rates (KCN incubations), and the proportion of lysogenic cells (mitomycin C inductions) were, respectively, 2.6-, 9.5-, and 2.2-fold higher in mucus than in the surrounding water. Both lytic and lysogenic indicators were tightly coupled with temperature and salinity, suggesting that the life strategy of viral epibionts is strongly dependent upon environmental circumstances. Finally, our results suggest that coral mucus may represent a highly favorable habitat for viral proliferation, promoting the development of both temperate and virulent phages. Here, we discuss how such an optimized viral arsenal could be crucial for coral viability by presumably forging complex links with both symbiotic and adjacent nonsymbiotic microorganisms.

The structure of the phytoplankton community in surface waters is the consequence of complex interactions between the physical and chemical properties of the upper water column as well as the interaction within the general biological community. Understanding the structure of phytoplankton communities is especially challenging in highly variable and dynamic marine environments. A variety of strategies have been employed to delineate marine planktonic habitats, including both biogeochemical and water-mass-based approaches. These methods have led to fundamental improvements in our understanding of marine phytoplankton distributions, but they are often difficult to apply to systems with physical and chemical properties and forcings that vary greatly over relatively short spatial or temporal scales. In this study, we have developed a method of dynamic habitat delineation based on environmental variables that are biologically relevant, that integrate over varying time scales, and that are derived from standard oceanographic measurements. As a result, this approach is widely applicable, simple to implement, and effective in resolving the spatial distribution of phytoplankton communities. As a test of our approach, we have applied it to the Amazon River-influenced Western Tropical North Atlantic (WTNA) and to the South China Sea (SCS), which is influenced by both the Mekong River and seasonal coastal upwelling. These two systems differ substantially in their spatial and temporal scales, nutrient sources/sinks, and hydrographic complexity, providing an effective test of the applicability of our analysis. Despite their significant differences in scale and character, our approach generated statistically robust habitat classifications that were clearly relevant to surface phytoplankton communities. Additional analysis of the habitat-defining variables themselves can provide insight into the processes acting to shape phytoplankton communities in each habitat. Finally, by demonstrating the biological relevance of the generated habitats, we gain insights into the conditions promoting the growth of distinct communities and the factors that lead to mismatches between environmental conditions and phytoplankton community structure.

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