Bacterioplankton dynamics along the gradient from highly eutrophic Pearl River Estuary to oligotrophic northern South China Sea in wet season: implication for anthropogenic inputs.

Bacterioplankton abundance (BA) and biomass (BB) from the eutrophic Pearl River Estuary (PRE) to the oligotrophic northern South China Sea (NSCS) were studied in the wet season. BA was significantly higher (p < 0.05) in PRE (12.51 ± 3.52 x 108 cells L⁻¹), than in the continental shelf neritic province (CSNP, 4.95 ± 2.21 x 108 cells L⁻¹) and in the deep oceanic province (OP, 3.16 ± 1.56 x 108 cells L⁻¹). Nutrient-replete PRE waters (DIN > 100 µM and PO4 > 1 µM) resulted in high chl a and BB, whereas nutrient-depleted offshore waters (DIN < 5 µM and PO4 < 0.5 µM) had low biomass. Temperature (> 26 °C) was not the controlling factor of BA. BB was significantly correlated with chl a biomass both in PRE and NSCS. The bacteria to phytoplankton biomass (BB/PB) ratio increased clearly along the gradient from near-shore PRE (0.15) to offshore CSNP (0.93) and deep OP (2.75), indicating the important role of small cells in the open ocean compared to estuarine and coastal zones.

Spatial and temporal dynamics of phytoplankton and bacterioplankton biomass in Sanya Bay, northern South China Sea.

The composition of phytoplankton and the dynamics of phytoplankton and bacterioplankton biomass (PB and BB, respectively) of Sanya Bay, South China Sea, were determined. A total of 168 species (67 genera) phytoplankton were identified, including Bacillariophyta (diatom, 128 species), Pyrrophyta (35 species), Cyanophyta (3 species), and Chrysophyta (2 species). Annual average abundance of phytoplankton was 1.2 x 10(7) cells/m3, with the highest abundance in autumn, and the lowest in summer. Annual average diversity index (H') and evenness (J) values were 3.96 and 0.70, respectively. Average chlorophyll-a was 2.5 mg/m3, and the average PB was 124 mg C/m3, with the highest value in autumn. Surface PB was higher than the bottom, except for summer. Annual mean bacterioplankton abundance and BB were 6.9 x 10(11) cells/m3 and 13.8 mg C/m3, respectively. The highest BB was found in summer, followed by winter, spring, and autumn. Surface BB was higher than bottom all year round. The spatial distribution patterns of PB and BB were very similar with the highest biomass in the estuary, and decreased seaward, primarily due to the terrestrial input from the Sanya River and influx of oceanic water. The main factor influencing PB and BB was dissolved inorganic nitrogen (DIN). Other factors such as temperature, which is above 22 degrees C throughout the year, had a negligible impact. The correlation between BB and PB was significant (P < 0.01). The annual average ratio of BB/PB was 0.12 (0.06-0.15). Phytoplankton primary production was one of the most important factors in controlling the distribution of bacterioplankton.