Environmental Stress Responses in the Size-Fractionized Phytoplankton in the Yalu River Estuary Waters
Marine phytoplankton are encountering novel challenges due to climate and environmental changes.Various indicators suggest that the imbalances in seawater nutrient concentrations,along with seawater warming and acidification,can cause a transition towards smaller-sized phytoplankton in marine ecosystems.However,this trend lacks direct confirmation and in-depth exploration in natural marine environments.This study established 16 sampling stations at the Yalu River Estuary,located in the northern Yellow Sea,and collected samples(including environmental DNA samples of phytoplankton and seawater)monthly from March to December 2020.A comprehensive analysis was conducted on size-fractionated phytoplankton and environmental indicators,including nitrogen,phosphorus,and silicon nutrients,water temperature,dissolved oxygen(DO),pH value,and chemical oxygen demand(COD).Non-metric multidimensional scaling(NMDS)correlation analysis was used to identify stations with varying gradients of different environmental factors.High-throughput sequencing and laboratory microscopic examination were combined to classify and quantify size-fractionated phytoplankton,aiming to assess their response to environmental variations in the Yalu River Estuary.The results show that the annual average concentrations of nitrogen nutrients in the Yalu River Estuary area are higher in the eastern and western estuarine regions and relatively lower in the central sea area.The distribution trends of phosphorus and silicon nutrients follows a similar pattern to nitrogen.pH values and DO levels are relatively low in the western estuarine region,while COD is relatively high in this area.Water temperature exhibits an inverted U-shaped trend from March to December,peaking in July.The verification results indicate that the concentrations of nitrogen,phosphorus,and silicon nutrients concentrations in seawater are negatively correlated with the biomass of smaller-sized phytoplankton,meaning that lower nutrient concentrations are associated with a higher biomass proportion of smaller-sized phytoplankton.Additionally,rising water temperatures also promote the growth of smaller-sized phytoplankton,further increasing their biomass proportion.Furthermore,it was found that smaller-sized phytoplankton demonstrate higher utilization efficiency of organic matter compared to larger-sized phytoplankton and show some tolerance to hypoxic conditions.This is evident in the increase in the proportion of biomass of smaller-sized phytoplankton with rising COD levels and a decrease with increasing DO levels.This study indicate that declining concentrations of nitrogen,phosphorus,and silicon nutrients,rising water temperatures,and increasing hypoxia in coastal sea areas collectively drive a shift towards smaller-sized phytoplankton in marine ecosystems.This shift could pose potential risks to ecosystem stability and the sustainable development of marine shellfish aquaculture.Therefore,in the context of global climate change,we recommend timely adjustments to policies regulating terrestrial nitrogen and phosphorus inputs in estuarine areas to support the health of marine ecosystems and promote sustainable marine economies.
phytoplanktonhigh-throughput sequencingsize-fractionatedenvironmental differenceYalu River Estuary waters
万方数据
维普
