Size-fractionated productivity and nutrient dynamics of phytoplankton in subtropical coastal environments

Abstract

It is now well established that the size distribution of phytoplankton plays an important role in primary production processes and nutrient dynamics of coastal environment. In situ observations showed that nanophytoplankton (3~20 μm) contributed 72.08% and 58.18% of phytoplankton biomass and 58.32% and 41.14% of primary productivity to Xiamen Western Waters and the northern Taiwan Strait, respectively; picophytoplankton (0.2~3 μm) dominated the biomass (64.70%) and productivity (66.09%) in the southern Taiwan Strait. Furthermore, nanophytoplankton accounted for 75% of phosphate uptake with the highest rate constant (8.3 × 10⁻⁵ s⁻¹) and uptake rate in unit water volume (5.4 × 10⁻⁵ mmol dm⁻³ s⁻¹); picophytoplankton had the highest uptake rate in unit biomass (5.4 × 10⁻¹ mmol mg⁻¹ s⁻¹) and photosynthetic index (3.8 mgC mgChl a ⁻¹ h⁻¹). All the results highlighted the remarkable characteristics of small size ranged (0.2~20 μim) phytoplankton in subtropical coastal environments: main contributor to phytoplankton biomass and production, high efficiency on organic carbon production and nutrient recycling. The far reaching environmental and ecological implications were discussed.