Institutional Repository of Key Laboratory of Marine Ecology & Environmental Sciences, CAS
|Alternative Title||Impacts of Kuroshio intrusion and its variation on harmful algal blooms in the sea area adjacent to the Changjiang River estuary|
|Place of Conferral||中国科学院海洋研究所|
|Keyword||长江口邻近海域 黑潮东海分支 原绿球藻 有害藻华|
长江口邻近海域是我国近海有害藻华高发区之一，有害藻华的发生不仅与陆源营养物质过量输入有关，也受到该海域复杂的水文、动力环境调控。以往研究认为，黑潮东海底层近岸分支 (Nearshore Kuroshio Branch Current, NKBC，以下简称黑潮东海分支)会影响到长江口邻近海域，有可能改变海域水文条件、水体结构和营养盐结构，进而影响浮游植物群落组成和分布状况，乃至有害藻华的发生过程。然而，目前对于黑潮分支调控有害藻华的过程和机理认识不足。本研究通过中国科学院海洋先导专项执行期间的野外调查，系统调查了黄、东海海域浮游植物类群组成和分布状况，重点分析了长江口邻近海域有害藻华发生情况及其与黑潮分支的关系，得到以下科学认识。
1. 调查分析了黄、东海海域微型与微微型浮游植物类群的丰度、分布状况及其季节变化特征，查清了几种典型有害藻华藻种在黄、东海海域的分布情况，明确了原绿球藻对东海黑潮分支输入的指示意义。应用流式细胞仪分析了2014~2015年间采自黄、东海的微型和微微型浮游植物样品 (粒径<20 mm)，结果表明各浮游植物类群存在不同的分布特点。微型真核藻类 (Photosynthetic nanoeukaryotes)主要分布在近岸海域。微微型真核藻类 (Photosynthetic picoeukaryotes)在近岸和外海均有高值分布区，但其类群组成存在明显差别。聚球藻(Synechococcus, Syn)在近岸和外海同样都有高值分布区，可能由不同生态型的聚球藻形成。原绿球藻(Prochlorococcus, Pro)主要分布在东海，在黑潮主干区丰度最高。聚类分析结果显示黄、东海浮游植物群落组成存在显著差异，在夏季更为明显。东海原甲藻 (Prorocentrum donghaiense)、米氏凯伦藻 (Karenia mikimotoi)等典型赤潮藻种主要分布在东海长江口邻近海域，尤以春季丰度最高，是有害藻华的高发时段。研究发现春季东海区原绿球藻的分布状况与黑潮东海分支路径基本一致，在近岸海域也有较高丰度的原绿球藻分布，表明黑潮东海分支能够将藻种从外海输入到长江口邻近海域。
2. 系统调查了黑潮东海分支的季节变异状况及其对长江口邻近海域微型与微微型浮游植物的潜在影响，发现春季是黑潮东海分支影响长江口邻近海域的重要时段。2015年2月至2016年1月在长江口邻近海域进行了周年逐月调查，水文数据 (温度、盐度)和微型、微微型浮游植物丰度的结果显示，黑潮东海分支自春季 (3月)在长江口邻近海域底部出现，夏季 (6月)强度最高，秋季减弱，冬季基本消失。原绿球藻和暗型聚球藻丰度的逐月动态特征与黑潮东海分支的强弱变化具有相关性和同步性。通过对比浮游植物和水团的关系，结合对台湾暖流影响过程的认识，确认了黑潮东海分支对长江口邻近海的影响在春季最为突出，初步揭示了黑潮东海分支对长江口邻近海域春季大规模有害藻华发生过程的潜在影响。
3. 对长江口邻近海域有害藻华发生情况进行了分析，初步揭示了黑潮东海分支及其变异对该海域甲藻赤潮发生过程的调控作用。研究发现，2015年长江口邻近海域的东海原甲藻在4月中旬即形成赤潮，比往年明显提前，同时伴有海链藻 (Thalassiosira spp.)赤潮，赤潮规模较往年明显偏小。米氏凯伦藻和亚历山大藻 (Alexandrium spp.)均未形成大规模的赤潮。调查期间，东海原甲藻在长江口邻近海域赤潮暴发时的温度约为14—18℃，明显低于往年东海原甲藻赤潮暴发时的海水温度。东海原甲藻赤潮的提前发生，应当与2015年黑潮东海分支较早出现并影响长江口邻近海域有关。黑潮东海分支的年际变异会对有害藻华发生过程、时间和规模等产生影响。
The sea area adjacent to the Changjiang River estuary is one of the most notable red-tide zone in the coastal water of China. Harmful algal blooms (HABs) occurred in this area are not only affected by the input of terrestrial materials, but also the hydrological conditions and hydrodynamical processes. Previous studies suggested that Nearshore Kuroshio Branch Current (NKBC) will influence the sea area adjacent to the Changjiang River estuary and hydrological, physical and chemical conditions, which will further affect the distribution and dynamics of phytoplankton communities and harmful algal blooms (HABs) in this area. However, the knowledge of Kuroshio intrusion on HABs is still quite limited. In this study, four seasonal cruises were conducted in the East China Sea (ECS) and the Yellow Sea (YS) from 2014 to 2016 to investigate distribution and composition of the phytoplankton in this area, and monthly cruises were organized at the same period in the sea area adjacent to Changjiang River estuary to study the impacts of NKBC variation on the occurrence of HABs. The major findings are as follows.
1. The abundance, distribution pattern and seasonal variation of pico-sized and nano-sized phytoplankton assemblages in the ECS and the YS were analyzed. Distributions of major HABs species were revealed, and the significance of Prochlorococcus as the indicator of NKBC was addressed. Four major pico-sized and nano-sized phytoplankton assemblages (diameter less than 20 mm), which were analyzed by flow cytometry, exhibited different distribution patterns in the ECS and YS. Photosynthetic nanoeukaryotes mainly distributed in the coastal waters. High abundance of picoeukaryotes were found in both coastal waters and subsurface offshore waters, which were composed of different groups of pico-sized microalgae. Cyanobacterium Synechococcus distributed in both coastal waters and offshore subsurface waters, resulting from at least two subgroups (ecotypes) of Synechococcus with different adaptive strategies. The distribution of Prochlorococcus was mainly confined in the ECS, and the abundance was the highest in the main stream of Kuroshio. Phytoplankton communities in the ECS and the YS showed distinct difference based on the results of cluster analysis, particularly in the summer. Cells of Prorocentrum donghaiense, Karenia mikimotoi and other typical causative species of HABs were mainly discovered in the sea area adjacent to Changjiang River estuary, and formed intensive HABs mainly in spring. The distribution pattern of Prochlorococcus in the ECS during investigation in spring well depicted the intrusion route of NKBC. High abundance of Prochlorococcus cells presented in the coastal waters in spring reflected the significance of NKBC in transporting the oceanic microalgae into the coastal waters adjacent to the Changjiang River estuary, one of the most significant red-tide zone in China.
2. Seasonal variation of NKBC and pico-sized and nano-sized phytoplankton assemblages were investigated in the sea area adjacent to Changjiang River estuary, and spring was considered as the most important season for NKBC to influence this area. Investigations were conducted every month from February, 2015 to January, 2016 in the sea area adjacent to Changjiang River estuary. Hydrological parameters indicated that high-salinity seawater at the bottom of the sea area adjacent to the Changjiang River estuary representing NKBC appeared in spring (March), peaked in summer (June), and almost disappeared in late autumn at the end of October. The dynamics of Prochlorococcus and the “dim” type Synechococcus abundance correlated well with the variation of NKBC. Water mass analysis further illustrated that spring was the critical season for NKBC to influence phytoplankton communities in the sea area adjacent to the Changjiang River estuary. The results further suggested that NKBC intrusion will impact the dynamics of HABs in this area.
3. Dynamics of HABs in the sea area adjacent to Changjiang River estuary were analyzed, and its relationship with variation of NKBC was discussed. In 2015, the dinoflagellate bloom of Prorocentrum donghaiense occurred in the sea area adjacent to Changjiang River estuary in mid-April, accompanied with the diatom bloom of Thalassiosira spp.. The intensity of the P. donghaiense bloom occurred much earlier than previous years, and the intensity of the bloom was also smaller. Abundance of dinoflagellates Karenia mikimotoi and Alexandrium spp. were fairly low and did not develop into large scale HABs. The temperature of seawater during the bloom of P. donghaiense was in a range of 14–18℃, which was significantly lower than the seawater temperature in other years during the bloom of P. donghaiense. The early occurrence of P. donghaiense was supposed to be relevant to the inter-annual variation of NKBC.
This study revealed the potential impacts of Kuroshio intrusion on the sea area adjacent to Changjiang River estuary, as well as the seasonal variation pattern of its impacts. Cyanobacterium Pro can be considered as an indicator for the intrusion of NKBC. The results also revealed the potential impacts of NKBC on dinoflagellate blooms in the sea area adjacent to Changjiang River estuary and the mechanisms. The results will offer strong evidence for a better understanding on the mechanisms of HABs in the sea area adjacent to Changjiang River estuary and for the development of sound prediction and forecasting strategies.
|MOST Discipline Catalogue||工学 ; 工学::环境科学与工程（可授工学、理学、农学学位）|
|赵越. 黑潮东海分支及其变异对长江口邻近海域有害藻华的影响研究[D]. 中国科学院海洋研究所. 中国科学院大学,2019.|
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