Size-Fractionated Net Primary Production Distribution and Its Environmental Control in the East China Sea During...

Area of Science:

• Marine ecology
• Biogeochemistry
• Oceanography

Background:

• Phytoplankton primary production (PP) is crucial for marine ecosystems, especially in winter marginal seas where it supports zooplankton and influences fish stocks.
• Understanding PP's magnitude and size structure is vital for predicting subsequent fishery resources.

Purpose of the Study:

• Investigate the spatial distribution, size structure, and environmental drivers of net primary production (NPP) in the East China Sea shelf during winter.
• Assess the light and nutrient controls on winter NPP and evaluate parameters used in satellite-based PP models.

Main Methods:

• Conducted two research cruises in the East China Sea shelf, a key fish overwintering ground.
• Measured NPP, nutrient concentrations, and light exposure (LE).
• Analyzed the size structure of NPP and compared in-situ model parameters (PBopt, F) with satellite-based predictions.

Main Results:

• Winter NPP was generally low, with light availability identified as the primary limiting factor due to sub-saturating light conditions.
• Nano-sized phytoplankton fractions dominated NPP, with a notable increase in the micro-sized fraction in February.
• In-situ measurements of PBopt and F were lower than model predictions, with deviations varying by water depth and mixing.

Conclusions:

• Light limitation, not nutrients, primarily controls winter primary production in the East China Sea shelf.
• The dominance of nano-phytoplankton shapes winter productivity, with implications for higher trophic levels.
• Current satellite-based NPP models may require refinement for accurate predictions in similar marginal sea environments, particularly regarding light-related parameters.