| In this research, the composition and distribution characteristic of the phytoplankton pigments in Changjiang Estuary and East China Sea were investigated. HPLC-CHEMTAX method was applied to assess phytoplankton taxonomic composition of Changjiang Estuary and East China Sea in 2009-2010, and the effects of environmental factors on phytoplankton pigment and community composition are studied as well. The purposes of this study were to offer some basic data for further exactly evaluating the eutrophication of Changjiang Estuary and East China Sea based on phytoplankton composition and pigments indicators. 21 kinds of pigments were detected in Changjiang Estuary and East China Sea. The major pigments were chlorophyll a, chlorophyll b, peridinin, fucoxanthin, 19'-butanoyloxyfucoxanthin, 19'- hexanoyloxyfucoxanthin, diadinoxanthin, alloxanthin and zeaxanthin. Chlorophyll a was the most abundant of all pigments, followed by fuxoxanthin and peridinin. The results show that the composition and distribution of phytoplankton pigments were influenced by light, temperature nutrients and many other environmental factors. The Chl a content was high in 122.5~123.5°E region, where the high concentration of fucoxanthin and peridinin were also observed in three cruise, indicating blooms of diatoms and dinoflagellates. Thus, in comparios with other regions, eutrophication level is serious in 122.5~123.5°E region. The mean Fp value of the studied waters was 0.76 (ranging from 0.16 to 0.98), which indicated the Changjiang Estuary was under medium eutrophication condition. Despite the higher nutrient concentrations, Fp value were lower in Turbidity Maximum zone than in the adjacent sea. However, with the further increase of the distance offshore, F_p value decreased significantly. The phytoplankton community, as determined by biomarker pigment concentration using HPLC and CHEMTAX, was composed mainly of diatoms, dinoflagellates, cryptophytes, chlorophytes, cyanobacteria, prymnesiophytes, chrysophytes and prasinophytes. The method was capable of detecteding algal groups generally underestimated or overlooked when using standard microscopic techniques. The distribution of mian phytoplankton groups had obvious regional characters, and it was mainly affected by dilute water. The phytoplankton community was characterized by high contribution of diatoms, cryptophytes and chlorophytes, and the abundances of prymnesiophytes, chrysophytes and cyanobacteria were increasing from inshore to open sea region.Preliminary in situ nutrient enrichment experiments were conducted in May and November, 2009 in the Changjiang River Estuary and adjacent areas to investigate phytoplankton composition response to nutrient addition. Results showed that the response of phytoplankton to nutrient was closely related to the nutrient limitation status of phytoplankton at sampling. Nutrient additions to natural water not only stimulate phytoplankton growth but also potentially alter the phytoplankton community structure. Due to the rapid growth rate of diatoms in nutrient replete conditions, diatom has more sensitivity response to nutrient input than other phytoplankton groups, shifting the community composition toward higher relative abundance of diatoms during the early stage of incubation. However, with the nutrient consumed by phytoplankton algal groups growing better in the condition with lower nutrients concentrations will comprise more portion of the total community biomass (μg Chl a / L) at the end of incubation. The results suggest that the effect of changing concentrations of nitrate and phosphate depend on the initial phytoplankton community present at the time of nutrient addition.Responses of growth, cellular total protein, carbohydrates and pigment composition in batch cultures of the marine dinoflagellate, Prorocentrum donghaiense, isolated from the Changjiang Estuary were studied in relation to different nutrient concentrations. The relationship between the nutrient concentrations and the physiological and biochemical responses were analyzed in order to provide some biological indicators for further exactly evaluating the eutrophication. Our laboratory data demonstrated that the nutrient concentration in the medium not only affected the growth, but also had a strongly effect on the biochemical composition of P. donghaiense. Protein content was significantly correlated with N concentration. P concentration did not have an obvious effect on protein. Cellular carbohydrates significantly accumulated in both N-limited and P-limited conditions. There was a significant negative correlation between cellular carbohydrates and the specific growth rate. The relationship between these biochemical parameters and initial nutrient concentrations showed the potential ability of specific ratios including cellular protein / carbohydrate, cellularβ-carotene / Chlorophyll a, cellular carbohydrate / cellular total P and protein / cellular total P as indicators of physiological status of phytoplankton.
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