Effects of inorganic nutrients on the phytoplankton community in the sea surface microlayer of Daya Bay, South China Sea

摘要

The sea surface microlayer (SML), which is the uppermost layer of the water column between the ocean and atmosphere, has unique physicochemical and biological properties and plays a significant role in biogeochemical processes. Water samples were collected from the SML of Daya Bay in Southern China between June and August of 2013. Algal growth potential (AGP) tests were conducted following the addition of different concentrations of inorganic nitrogen (N), phosphorus (P) and silicate (Si) under laboratory conditions. The purpose of this study was to evaluate the effects of nutrient enrichment on phytoplankton in the SML. Chl a increased significantly after nutrient addition, and the biggest increase occurred in test groups with the addition of three nutrient elements. Nutrient concentrations decreased sharply, along with the growth of phytoplankton. Photoprotective carotenoids (PPCs) generally decreased after nutrient addition, while photosynthetic carotenoids (PSCs) became prominent after nutrient addition. Phytopigments were dominated by zeaxanthin (Zea), which contributed to 36.7%-79.4% of the total accessory pigments (TAcc). The next most abundant pigment was fucoxanthin (Fuco), with proportions of 15.2%-39.3%. Percentages of Zea decreased significantly after nutrient addition, and those of Fuco increased accordingly. The results suggest that the phytoplankton in the SML in Daya Bay is dominated by cyanobacteria followed by diatoms but that nutrient addition (i.e. eutrophication) might lead to a switch in dominance.