海洋生态与环境科学重点实验室知识库

近年来，全球范围内海洋生态灾害频发，严重影响了海洋生态系统的健康及可持续发展目标。水母暴发作为一种全球性的海洋生态灾害，自上世纪80年代以来呈现出暴发规模越来越大、频率越来越高的趋势。作为生态系统中的“盲端”，大规模水母暴发一方面会大量摄食或杀死水体中的浮游动物，与鱼类等生物竞争饵料，破坏生态系统的结构和功能，影响渔业资源产出；另一方面会堵塞工厂或船舶的冷却水系统，蜇伤游客，影响滨海旅游业发展，给经济社会发展带来严重威胁。

在我国近海暴发的水母主要有海月水母、沙海蜇和白色霞水母等，其中，沙海蜇广泛分布在我国北纬30度以北的渤、黄、东海海域。大型水母的暴发和分布与气候变化、富营养化、栖息地的改变、食物网结构以及物理海洋过程等因素密切相关。大量研究发现，沙海蜇从长江口以北海域萌发到夏季暴发旺盛期的分布均只限于30°N以北的海区，基本未出现在30°N以南的区域。本文基于沙海蜇暴发过程中的地理分布特征，从浮游食物网、海洋环境因子及物理过程的角度对沙海蜇的分布格局进行了关键过程和控制因素的分析和研究。

基于2016年8月和2017年8月两个航次的大面调查，进行了沙海蜇暴发期黄海和东海的食物网分布格局研究。结果表明，浮游植物及浮游动物的丰度和生物量均呈现南高北低的分布格局，东海区浮游植物及浮游动物生物量均高于长江口附近，而长江口附近及东海区浮游动物功能群结构则无明显差异。通过对浮游食物网能量传递、浮游动物种类组成和数量等综合分析结果表明黄、东海海区浮游食物网时空分布格局及结构不足以构成沙海蜇向南不能逾越30°N的主要障碍。

为进一步深入分析沙海蜇分布格局与浮游食物网时空分布及相关环境因子的关系，探究沙海蜇只限于30°N以北海域分布的深层原因，将研究海区选在30°N南北两侧27°N-33°N之间的长江口邻近海域。基于2015年8月-2017年8月3个年度的夏季调查数据，探究沙海蜇分布与浮游生物群落及环境因子之间的关系。基于ZooScan图像扫描技术分析，将浮游动物分为小型桡足类、大型桡足类、大型甲壳类、被囊类、毛颚类和小型水母类六个功能群。小型桡足类在丰度上占据绝对优势，而小型水母类则是体积生物量的优势类群。浮游动物功能群在三年间的变化趋势是先升后降，这可能与海水表层温度的变化有关。三年间，甲壳类功能群基本保持稳定，胶质类功能群波动较大，被囊类和毛颚类在2016年达到高值期，而小型水母类在2017年显著下降；不同浮游动物功能群的分布模式各异，基本的分布高值区集中在福建、浙江沿岸和黄、东海交界线海域，验证了黄东海交汇区小型桡足类、大型桡足类、被囊类和小型水母类功能群在30°N南北两侧海域不具有显著差异性，仅大型甲壳类和毛颚类在2015和2017年具有显著差异。沙海蜇在2015-2017年丰度和生物量都呈上升趋势，且在30°N站位及以南很少或无分布，这与浮游动物功能群丰度及体积生物量不具有明显相关性，只在2017年与小型桡足类和毛颚类存在极显著相关关系。沙海蜇与叶绿素a呈现正相关而与盐度呈现负相关，进而推测沙海蜇在长江口附近的分布模式受该区域的物理海洋过程驱动。

在研究了黄、东海特别是长江口附近浮游食物网结构及环境因子的基础上，将重点放在北纬30度附近的物理过程上。5月底、6月初，沙海蜇碟状体和幼体开始出现在长江口以北海域，到8月，其分布范围和生物量达到一年中的高峰期，随后开始消亡。沙海蜇生物量峰值出现在8-9月。

对物理海洋过程的研究表明，长江冲淡水、东海环流和黑潮对沙海蜇分布起主要影响，其中，长江冲淡水的作用较为明显，冲淡水锋面的存在一定程度上对沙海蜇碟状体或幼体在更大范围的分布起到约束作用，而在夏季北向流动的东海沿岸流、台湾暖流和黑潮作为输送屏障的存在，也阻止了沙海蜇被带向纬度较低海域的可能。

In recent years, marine ecological disasters occur globally, which seriously affect the health of marine ecosystems and sustainable development of the blue economy. As a global marine ecological disaster, jellyfish blooms have been increasing in the scale and frequency since the 1980s. Jellyfish blooms seriously effect on the food web of the marine ecosystem and fish population, because it feed on zooplankton include fish larvae. Jellyfish bloom could block the cooling water system of factories along the coast, affect coastal tourism, and bring great threat to the development of blue economy.

The blooming jellyfish in Chinese waters mainly include Aurelia aurita, Nemopilema nomurai and Cyanea nozakii. Among them, Nemopilema nomurai is widely distributed in the Bohai Sea, Yellow Sea and East China Sea to the north of 30°N. The outbreak and distribution of large jellyfish are closely related to climate change, eutrophication, habitat change, feeding, and physical ocean processes. A large number of studies have found that the distribution of Nemopilema nomurai sprouting from the waters north of the Yangtze Estuary to the summer bloom period is limited to the area north of 30°N in the Yangtze River Estuary, and almost does not appear in the area south of 30°N. Based on the geographical distribution characteristics of the outbreak process of Nemopilema nomurai, the key processes and controlling factors of the unique distribution pattern of Nemopilema nomurai were analyzed and studied from the perspectives of planktic food web, marine environmental factors and physical processes.

Firstly, based on the large-scale survey of two voyages in August 2016 and August 2017, the distribution pattern of food web in the Yellow Sea and East China Sea during the outbreak period of Nemopilema nomurai was studied. The results showed that the abundance and biomass of phytoplankton and zooplankton were higher in the south than in the north, and the biomass of phytoplankton and zooplankton in the East China Sea was higher than that in the Yangtze River Estuary, but there was no significant difference in the structure of zooplankton functional groups between the Yangtze River Estuary and the East China Sea. From the perspectives of energy transfer, quantity and quality of planktonic food web, it is suggested that the spatial and temporal distribution pattern and structure of planktonic food web in the Yellow and East China Seas is not the main reason for the inability of Nemopilema nomurai to distribute southward beyond 30°N in summer.

In order to further analyze the relationship between the distribution pattern of Nemopilema nomurai and the spatial and temporal distribution of plankton-food web, the study area was focused in the waters adjacent to the Yangtze River Estuary between 27°N-33°N around 30°N. Based on the survey data from August 2015 to August 2017, the relationship between the distribution of Nemopilema nomurai and plankton community and environmental factors was checked. zooplankton sample were analyzed with ZooScan image system, zooplankton were divided into six functional groups: small copepods, large copepods, large crustaceans, salps, chaetognaths and small medusae. Small copepods dominated in abundance, while small medusae were the dominant group in biovolume. It was verified that the functional groups of small copepods, large copepods, salps  and small jellyfish in both sides of  30°N did not show significant differences. Only large crustaceans and chaetognaths showed significant differences between 2015 and 2017. The abundance and biomass of Nemopilema nomurai showed an increasing trend from 2015 to 2017, and there was little or no distribution at the 30°N stations and south of  30°N. This was not significantly correlated with the abundance and biovolume of zooplankton functional groups, but only with small copepods and chaetognaths in 2017. There was a positive correlation between chlorophyll-a and Nemopilema nomurai, and a negative correlation between chlorophyll-A and Nemopilema nomurai. It was inferred that the distribution pattern of Nemopilema nomurai in the Yangtze River Estuary area was driven by the physical ocean processes.

On the basis of planktic food web structure and environmental factors in the Yellow Sea and East China Sea, especially in the Yangtze River Estuary area, it is demonstrate that the distribution pattern of Nemopilema nomurai north of 30°N in summer is mainly caused by the physical process. At the end of May and the beginning of June, Nemopilema nomurai larvae began to appear in the waters north of the Yangtze River Estuary. By August, the distribution range and biomass of Nemopilema nomurai reached the peak of the year, and then began to disappear.

Research has shown that the discharge of Yangtze River diluted water, Taiwan warm current and Kuroshio current branch main influence to the distribution of Nemopilema nomurai, the existence of Taiwan warm current, the East China Sea circulation and Kuroshio transport barrier, flowing to the north, prevents Nemopilema nomurai from being carried to lower latitudes.