黄海绿潮消退后漂浮绿藻归宿及其生态效应研究

Large-scale green tides formed by green alga Ulva prolifera occurred consecutively in the Yellow Sea over the last 9 years from 2007. The green tides in the Yellow Sea, which are different from green-tide events in other regions around the world, have huge biomass of green algae about several million tonnes, and impact an extensive area up to 30 thousand square kilometers. The formation and decline of such extensive blooms with huge algal biomass will definitely affect the biogeochemical processes of major biogenic elements such as nitrogen and phosphorus, and probably affect the structure of the phytoplankton community in a specific region, or even lead to the occurrence of derived ecological disasters like red tides or hypoxia. However, there is little knowledge on the fate of large amounts of floating green algae in the Yellow Sea and their impacts on marine ecosystems after the decline of green tides. This project is planed to perform analysis on a specific biomarker for green algae in genus Ulva, 28-isofucosterol, in the sediment to trace the sedimentation region of green algae, and to find out the effects of decomposed green algae on the phytoplankton community and the possibility of derived ecological disasters through field investigations and simulation experiments in the laboratory. The findings of this project will help to fully understand the ecological impacts of green tides, promote our knowledge on the ecosystem changes and their driving forces, and offer important data on the assessment and prevention of marine ecological disasters.

自2007年以来，南黄海海域的大规模浒苔绿潮已经连续9年发生。与世界上其他沿海地区的绿潮不同，黄海海域的绿潮规模大、影响范围广，如此大范围、大规模的藻华现象，会影响黄海海域生源要素的生物地球化学过程，有可能改变局部海域浮游植物现存量和群落结构，甚至引发次生灾害。但是，目前对于黄海绿潮的生态效应，尤其是绿潮后期大量漂浮绿藻的最终归宿及其死亡分解后造成的生态效应缺少科学认知。本项目计划通过对沉积物中石莼属绿藻生物标志物28-异褐藻甾醇的分析，寻找黄海大量漂浮绿藻的沉降区域，并通过对绿藻沉降区特定时段浮游植物群落结构的分析，结合模拟实验，研究绿潮消退后大量绿藻死亡分解对浮游植物群落结构的影响，分析其导致次生灾害的可能性，所得到的结果将有助于全面理解黄海绿潮的生态效应，促进对海洋生态系统演变及其驱动因子的科学认识，也可以为绿潮灾害的评估和防控提供更多的科学依据和支撑。

自2007年以来，由绿藻浒苔(Ulva prolifera)形成的绿潮在南黄海海域连年出现。黄海海域的绿潮规模大、影响范围广，对黄海海域生态系统的影响备受关注。对此，本项目从大量漂浮绿藻的沉降区域追踪入手，探讨了黄海绿潮后期大量绿藻沉降、分解导致的生态环境效应。项目选择28-异褐藻甾醇作为漂浮绿藻的生物标志物，分析了其对我国近海主要有害藻华种类指示的特异性，以及在环境中的稳定性状况，探索了以表层沉积物中28-异褐藻甾醇分布和含量状况追踪漂浮绿藻沉降区的方法。通过在黄海海域连续三年的大面调查，获得了沉积物中28-异褐藻甾醇的含量和变化状况，结合现场底拖网调查和海域沉积物粒度组成与碳、氮含量，推断山东半岛东南部海域（36-36.5°N，121-123°E）为漂浮绿潮藻类的主要沉降区。通过宏基因组学和宏转录组学手段，跟踪分析了沉降区浮游植物群落结构特点及变化特征，发现在绿藻沉降前后浮游植物类群组成与相对丰度有显著变化，海金藻和微型绿藻等浮游植物类群的变化尤为明显，推测与外海水入侵及绿藻沉降分解过程有关。模拟实验结果也发现，与绿藻沉降分解有关的环境变化有可能促进特定浮游植物类群的生长。通过对柱状沉积物的分析发现，沉降区甲藻优势度和底层溶解氧水平存在下降趋势。研究结果有助于深入了解黄海绿潮的生态效应，也将为绿潮灾害评估和防控提供更多的科学依据和理论支撑。