No abstract

the paper showed the variation of water quality parameters by time. The concentration of total suspended sediment, chlorophyll-a, dissolved inorganic nitrogen, dissolved inorganic phosphorus and ratio of N:P changed significantly by season. The results of assessing water quality by UNTRIX (integrated concentration of Chlorophyll-a, dissolved inorganic nitrogen, dissolved inorganic phosphorus and level of saturated oxygen) indicated the quality levels were increased

Coral associated bacteria and their host are currently one of the interested issues for research and scientists worldwide. The densities of zooxanthellae and bacteria associated with three most prevalent species Acropora hyacinthus, Acropora muricata and Acropora robusta in Hang Rai, Ninh Thuan was evaluated over time by staining with SYBR Gold and direct counting with epifluorescence method. The most dominant bacteria were isolated by culture dependent method. The densities of zooxanthellae and bacteria ranged from 0.39–1.83×107 cell/g, and 0.83–2.52×108 cell/g, respectively. Bacterial density in the 3 months was significantly different compared to the density of the bacteria in ambient water. Total heterotrophic bacteria, comma shaped bacteria and bacillus form showed negatively correlated with pH, PO4, while zooxanthellae showed no correlation with all factors.

Primary production (PP) of phytoplankton plays an essential role in food web dynamics, biogeochemical cycles and marine fisheries. It is used as one of the basic information for evaluating marine ecosystems. In this paper, monthly composite PP data on a 4 km x 4 km grid for the period 2003-2020 was used to evaluate the distributional characteristics of PP in the coastal marine area of Vietnam South Centre. The statistical results show that the climatological average of PP in 18 years reached 449.2 mgC/m2/day, ranged from 272.1 to 14,205.4 mgC/m2/day. The PP has seasonal and spatial variations. In time, the lowest value of PP was in spring, and the highest was in winter; in space, PP tended to decrease from shore to offshore, PP was higher in coastal areas than in the open sea areas. During the northeast monsoon season, PP increased by more than 1000 mgC/m2/day in the coastal area. Meanwhile, in the southwest monsoon season, due to the ecological influence of the upwelling phenomenon, PP increased with a value greater than 1500 mgC/m2/day, distributed along the coastline of Ninh Thuan - Binh Thuan. Primary productivity positively correlated with chlorophyll content but negatively correlated with sea surface temperature with correlation coefficients of 0.9 and -0.6, respectively. There was a weak correlation between PP and ONI with correlation coefficients of -0.23. The temporal-spatial variation of PP was affected by the ENSO (El Niño-Southern Oscillation) phenomenon, the positive phase of ENSO (El Niño conditions) corresponded to lower PP, and the negative phase of ENSO (La Niña conditions) corresponded to higher PP. The research results from this paper can be used as a reference in marine ecosystem management.

The uptake rate of nitrate by leaves and roots was simultaneously investigated in the seagrass T. hemprichii collected from Lo river, Nha Trang. The principle of nutrient uptake of seagrass was based on the approaches of the Michaelis-Menten model. The laboratory experiments of nitrate uptake were done the ranges of ambient nitrate concentrations in the separate water column of leaves and roots. The calculated results indicated that the nitrate uptake rate through the leaves was higher than that of the roots. The maximum uptake rate (Vmax) through the leaves and the roots was 1,777.0 mgN/g DW/h and 131.6 mgN/g DW/h, respectively. From these results, the nitrate uptake rate by the seagrass in Lo river was estimated at 52.2 mgNm-2h-1. The value plays an important role in developing and implementing plans for the protection and rehabilitation of seagrass beds in coastal areas.