南黄海苏北浅滩及邻近海域浒苔微观繁殖体越冬机制研究

The large-scale green tide has been prevailing in the western Yellow Sea for over ten years, resulting in substantial economic losses and serious social impacts. Years of research revealed an early development process of the green tide, in which the floating Ulva prolifera biomass was consistently initiated from Subei Shoal and the adjacent coastal water of southwestern Yellow Sea. Whereas, it remains unclear about the invisible pre-bloom process of the green tide in this origin region. Micropropagules, as the important seed source for the green tide, are widespread in Subei Shoal and the adjacent coastal waters, and are hypothesized playing important functions during the pre-bloom process. However, the underlying mechanism for this pre-bloom process needs further investigation, including what cell types those micropropagules are, how the Ulva prolifera micropropagules tolerate the advent environmental conditions in winter and maintain its population. Therefore, this research project is proposed to study the overwintering strategies of U. prolifera micropropagules in Subei Shoal and the adjacent coastal water, including cell forms, spatial and temporal distribution of micropropagules, the recruitment process and the special ecological and environmental conditions in this region that could influence and regulate this process etc. This work is going to help fully eliminate the formation mechanism of the consecutive large-scale green tide, and further assist developing prevention and controlling measures in the source region of the green tide.

大规模浒苔绿潮在黄海西部连年爆发，造成重大经济损失和显著社会影响。目前，对于黄海绿潮的早期发生发展过程已形成较为统一的认识，南黄海苏北浅滩及其邻近海域是黄海绿潮起源与形成的重要区域；然而，对于绿潮在该海域不可见的孕育过程还存在较多的分歧。微观繁殖体在浅滩及邻近海域普遍存在，被认为是绿潮浒苔越冬的重要方式，并在绿潮的孕育与形成中发挥重要作用。但浒苔微观繁殖体在该海域具体以何种方式越冬、如何越冬、维持种群，为翌年春季爆发提供种源，这些问题还未有全面、深入的研究，这也是解析黄海绿潮连年在该海域起源与形成的关键所在。本项目拟对苏北浅滩及邻近海域浒苔微观繁殖体越冬的主要方式、细胞形态、时空分布特征、萌发过程和条件进行现场调查和模拟实验，并结合该海域特殊的生态环境条件，阐明浒苔微观繁殖体在浅滩及邻近海域的越冬机制，以期深入揭示黄海浒苔绿潮连年爆发的内在原因，并为黄海绿潮源头防控提供理论指导和技术支撑。

黄海浒苔绿潮已连续暴发十余年。目前我国对于黄海绿潮的发生发展过程和暴发机制已开展详细的调查研究，并取得丰富的研究成果，但浒苔微观繁殖体以何种方式越冬、如何越冬、维持种群，为翌年春季爆发提供种源，这些问题还未有全面、深入的研究，这也是解析黄海绿潮连年在该海域起源与形成的关键所在。项目通过历史资料对比分析、现场调查和实验研究等手段，研究了南黄海浒苔微观繁殖体分布规律及其影响要素，探索了浒苔微观繁殖体主要细胞形式、底栖昌螺和附生钩虾对微观繁殖体库的贡献，并研究开发了浒苔微观繁殖体快速检测方法。研究发现不同时期和不同区域，浒苔微观繁殖体分布及其影响要素有所不同。浒苔绿潮暴发期，微观繁殖体在南黄海广泛分布，主要集中在水深30米以浅的表层水体中，其丰度与漂浮浒苔密度呈正相关，而与漂浮铜藻呈反比关系；非浒苔绿潮暴发期，南黄海水体中微观繁殖体较少，主要集中在近岸海域。对山东-江苏近岸调查发现，苏北浅滩微观繁殖体丰度始终较高，浒苔（尤其是是“漂浮型”浒苔）占比高。对苏北浅滩海域的精细化调查研究表明，筏架是浒苔微观繁殖体分布的主要影响因素，繁殖体丰度与筏架的距离呈显著负相关，秋冬季潮沟底部微观繁殖体丰度高于表层。附生钩虾啃食对微观繁殖体库有明显的贡献，浅滩底栖昌螺对微观繁殖体库及其萌发有一定的作用。浒苔微观繁殖体存活率受所处环境类型、温度和光照条件的影响较大。在水体中，浒苔微观繁殖体在弱低温（5°C）和低光照条件下，可保持较高的存活率；在沉积物中，微观繁殖体在低光照条件下能保持一定的存活率（1个月存活率可达50%左右），光照强度增加，存活率下降；浒苔微观繁殖体最适萌发温度为15-20°C。综上所述，苏北浅滩越冬浒苔微观繁殖形式多样，以藻体碎片为主，浅滩筏架周围存在高值区，可在潮沟底层、沉积物中存活越冬；项目研发了定量PCR检测浒苔微观繁殖体的方法，为浒苔绿潮监测和防控提供有力的技术支撑。