Phytoplankton Functional Groups In The Yellow Sea And The East China Sea

Phytoplankton is the main component of primary producers in the ocean, which triggers the energy flow and material flow of marine ecosystem, and initiates the pelagic food web. Food web from end to end is the core target of 973 key project―Key processes and sustainable mechanism of food output in Chinese coastal pelagic ecosystem‖. Trophic dynamics of plankton functional groups is one of the key scientific issues. Therefore, it is critical to study the composition and ecological characteristics of phytoplankton functional groups (PFGs) in the Yellow Sea (YS) and the East China Sea (ECS).From April 2006 to June 2008, nine cruises were conducted in the YS and the ECS. Based on phytoplankton data by Unterm?hl method, composition and ecological characteristics of PFGs were investigated. Relationships between PFGs and environmental factors were analyzed by CCA, and influences of hydrodynamic processes on PFGs were taken in account as well.According to trophic function, phytoplankton is divided into 12 functional groups, i.e. pico-phytoplankton (PicoPl), nano-diatom (NanDiat), autotrophic nano-flagellate (NanAutFl), autotrophic micro-dinoflagellate (MAutFl), mixotrophic micro-dinoflagellate (MMixFl), heterotrophic micro-dinoflagellate (MHetFl), unicellular micro-diatom (MUniDiat), hair-shaped micro-diatom (MHairDiat), branch-shaped micro-diatom (MBranDiat), toxic phytoplankton (ToxPl), inedible phytoplankton (InedPl), and other phytoplankton (Others).Phytoplankton integrated biomass in spring was much higher than that in autumn in the southern YS. High biomass distributed in the coastal water of Shandong Peninsula in spring, whereas, in the coastal water of Cheju Island in autumn. Phytoplankton integrated biomass showed evident seasonal variation in the Yangtze River Estuary (YRE) and its adjacent waters, i.e., in summer > in spring > in autumn > in winter. Biomass in the coastal waters of YRE and Zhejiang Province was much higher than that in off-shore sites with salinity > 31. Vertically, phytoplankton biomass decreased with depth from surface to bottom.Composition of PFGs varied spatially and temporally in the YS and the ECS. MHairDiat was the most dominant group in the southern YS in spring and autumn. MHetFl-dominant dinoflagellate groups were most important, in addition, ToxPl was also important in the YRE and its adjacent waters in late spring. Diatom groups replaced dinoflagellate, and MHairDiat and MBranDiat were dominant in the YRE and its adjacent waters in the middle of summer. Diatom groups accounted for 95% of phytoplankton biomass in the YRE and its adjacent waters in late summer. Diatom groups, MHairDiat > MUniDiat > MBranDiat, were dominant in the continental shelf water of ECS in autumn and winter. Dinoflagellate groups, MMixFl > MAutFl > MHetFl, were dominant in the YRE and the coastal ECS in May of 2007, while MHetFl > MMixFl > MAutFl in June of 2008.MHairDiat was most abundant in the YS Trough water near Shandong Peninsula in spring. Its biomass in the YRE and the coastal ECS increased from late spring to late summer, and decreased from autumn to winter. MHairDiat showed extremely low biomass in the Yellow Sea Cold Water Mass (YSCWM) area in autumn. Distribution of MUniDiat was similar to that of MHairDiat in spring. Its biomass in the YRE and the coastal ECS increased from August to October. MUniDiat was more abundant in the ECS than in the southern YS in autumn. MUniDiat biomass in winter was lower than that in autumn in the ECS, and was densely distributed near the YRE. In spring, MBranDiat was abundant in the YS water near the YRE, while scarce in the ECS. MBranDiat biomass increased from June to October, and decreased from autumn to winter in the ECS. Late spring peak value appeared in coastal water of Hangzhou Bay, while autumn peak value in the open sea. In autumn MBranDiat was densely distributed in the coastal water of YS. High density of MHetFl located in coastal water of Shandong Peninsula and the area near the YRE and Hangzhou Bay in spring. MHetFl biomass was much low in the YS and the ECS from summer to winter. MMixFl biomass was highest in late spring among four seasons, and its peak value occurred in the YRE and the coastal ECS. MMixFl biomass was higher in the ECS than in the YS in spring, while lower in the ECS than in the YS in autumn. MMixFl biomass was extremely low in the continental shelf water of ECS in winter. Maximum MAutFl biomass occurred in the YRE adjacent YS in late spring, and high biomass decreased in summer. MAutFl was in low abundance in the continental shelf water of ECS in autumn and winter. ToxPl was abundant in the middle of southern YS, in the YRE and the coastal ECS in spring, and showed peak biomass, which disappeared in late summer, in the YRE adjacent YS in the middle of summer. InedPl was most abundant in the YRE adjacent YS in late summer. Generally, its biomass was high in open sea.Succession of keystone species was evident in survey area. Keystone species were mainly diatoms in the southern YS. Keystone species were Thalassiosira pacifica and Corethrom hystrix in spring, and Guinardia striata and Coscinodiscus sp. in autumn. In the YRE and the ECS, dinoflagellates, such as Noctiluca scientillans, Prorocentrum dentatum, Karenia mikimotoi, became keystone species in May and June, besides toxic phytoplankton Pseudo-nitzschia delicatissima showed high biomass as well. Diatom, i.e. Dactyliosolen fragilissimus, Chaetoceros curvisetus, Rhizosolenia crassipina, Lauderia annulata, replaced dinoflagellate and became keystone species in summer. Diatoms, such as Coscinodiscus sp., Thalassiosira rotula, Guinardia striata, became keystone species again in autumn. Keystone species in winter was mainly unicellular diatom, such as Coscinodiscus sp.. Noctiluca scientillans, Prorocentrum dentatum, and Karenia mikimotoi could bloom in the YRE and its adjacent water in spring, so could Thalassiosira pacifica in the southern YS in spring.Correlations between PFGs and environmental factors were highly variable in spatial and temporal scale. MHairDiat was well correlated with salinity and temperature in survey area, however, it could be limited by nutrients during cruise LST-I and cruise QYQ-II. Distributions of MUniDiat were mainly influenced by nutrients, but also correlated with salinity during cruise LST-I. Distributions of MBranDiat could be influenced by nutrients in spring and summer, while by temperature and salinity in late summer, autumn and winter. Phosphate was the key factor that influenced the distributions of MAutFl during cruise LST-I, while ammonia in the Yangtze River Estuary, and nutrients during cruise ZLJ-I, and temperature and salinity during other cruises. MMixFl well correlated with temperature and salinity, whereas correlated with nitrogen during cruise LST-I and cruise ZLJ-I. MHetFl mainly distributed in upper layers of coastal waters, however, it could show high biomass in open sea as well. ToxPl was mainly influenced by nitrogen during cruise LST-I, cruise QYQ-II, and cruise ZLJ-II. Distributions of InedPl were mostly controlled by temperature and salinity, in addition, InedPl positively correlated with nutrient during cruise ZLJ-I and cruise ZLJ-II.Phytoplankton biomass was extremely low in the YSCWM in autumn, where the strong thermocline stopped the upward transport of nutrients from bottom water. There was mainly phosphate limitation in surface water, where MMixFl and MHetFl were dominant, and illumination limitation below surface, where MUniDiat was dominant. High phytoplankton biomass in the YRE was supported by rich nutrients transported by Yangtze River Dilute Water. Phytoplankton biomass front appeared in the waters where nutrients and illumination stroke a balance. Phytoplankton biomass was generally low in Kuroshio and Taiwan Warm Current, characteristic of high salinity and low nutrients.Cluster analysis of survey sites of every cruise was conducted based on PFGs composition. According to cluster analysis and phytoplankton biomass, the YS and the ECS were divieded into several provinces. The southern YS were divided into 4 provinces in spring, while 3 provinces in autumn. The YRE and its adjacent YS and ECS was divided into 2 provinces in late spring, and 4 provinces in the middle of summer, and 3 provinces in late summer. The continental shelf water of ECS was divided into 2 provinces in both autumn and winter. The YRE and the coastal ECS were divided into 2 provinces in spring and 3 provinces in late spring.PFGs provinces were similar to zooplankton functional groups provinces in the southern YS in spring and autumn, however, they were quiet different in distribution of biomass. Biomass and composition of PFGs was closely correlated with grazing, metabolism, and reproduction of Calanus sinicus. High biomass of MHairDiat and MBranDiat could be a key factor in formation of hypoxia in the YRE in summer.Based on carbon biomass, the composition and distributions of PFGs were reported in the YS and the ECS, so was the distribution of keystone species. Correlations between PFGs and environmental factors were analyzed, and PFGs provinces were divided as well. This dissertation provides for the food output model in the YS and the ECS. To understand the PFGs comprehensively, multi-method should be employed in the analysis of phytoplankton samples. Furthermore, interdisciplinarity study should be conducted to get insights into trophic structure of pelagic food web in the YS and the ECS.