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 10(8) cells L-1), than in the continental shelf neritic province (CSNP, 4.95 +/- 2.21 x 10(8) cells L-1) and in the deep oceanic province (OP, 3.16 +/- 1.56 x 10(8) cells L-1). Nutrient-replete PRE waters (DIN > 100 mu M and PO4 > 1 mu M) resulted in high ch1 a and BB, whereas nutrient-depleted offshore waters (DIN < 5 mu M and PO4 < 0.5 mu M) had low biomass. Temperature (>26 degrees C) was not the controlling factor of BA. BB was significantly correlated with ch1 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. (C) 2011 Elsevier Ltd. All rights reserved.