长江口及邻近海域凤鲚生境履历重建

利用X-射线电子探针微区技术(EPMA)对长江口崇明和邻近吕四凤鲚(Coiliamystus)耳石Sr和Ca的微化学进行了分析。定量线分析和Sr含量面分布图谱显示,凤鲚耳石核区的Sr/Ca比值存在Sr/Ca3、3Sr/Ca7和Sr/Ca7这3种类型,分别对应的耳石核心面分布同心环区域颜色为蓝色、绿色和黄-红色,据此推断长江口及邻近海域凤鲚孵化场存在3种,即淡水孵化场、河口半咸水孵化场及海水孵化场。凤鲚个体耳石从核心到边缘的Sr/Ca比值变化波动极为显著,有对应淡水生活的低值阶段(Sr/Ca3,最小为2.04±0.87),也有对应海水生活的高值阶段(Sr/Ca7,最大为7.81±0.91),可将凤鲚的生境履历类型分为4种类型:淡水–河口半咸水型、河口半咸水定居型、河口半咸水–海水型和淡水–河口半咸水–海水型。长江口邻近海域吕四凤鲚有淡水和河口半咸水孵化个体,其生境履历类型包括淡水–河口半咸水型、河口半咸水–海水型和淡水–河口半咸水–海水型,而长江口崇明岛海域有海水及河口半咸水孵化个体,其生境履历类型包括淡水–河口半咸水型、河口定居型及淡水–河口半咸水–海水型,这反映了长江口崇明岛及邻近海域吕四2个海域凤鲚个体间的共性以及差异性。通过本次研究,首次证明了长江口及邻近海域凤鲚存在3种孵化场及4种生境履历类型,准确反映了凤鲚个体组成及其生活史的多样性和复杂性。

Habitat history reconstruction of Coilia mystus from the Yangtze River Estuary and its adjacent sea area

As an important fishery resource in the Yangtze Estuary, Coilia mystus has high nutritional value and delicious taste. Because of overfishing, environmental pollution, and habitat degradation in recent years, the resources of C. mystus have declined sharply. As a type of migratory fish, the growth, development, and reproduction of C. mystus are affected by the freshwater, estuarine brackish water, and seawater environment. Therefore, exploring the habitat history of C. mystus is of great importance in the protection and management of this resource. To study the habitat history of C. mystus in the Yangtze Estuary and its adjacent sea area, otolith microchemical analysis of 10 C. mystus from Chongming Island in the Yangtze Estuary and its adjacent Lvsi sea area was conducted using X-ray electron probe microanalysis techniques. Quantitative line analysis and surface distribution of Sr content showed that Sr/Ca ratios in the otolith core area of C. mystus existed in Sr/Ca<3, 3C. mystus could be divided into three types:the freshwater incubation field, estuarine brackish water incubation field, and sea water incubation field. The variation in Sr/Ca ratios in the individual otoliths from the core to the edge was highly significant, including low-ratio freshwater habitat (Sr/Ca<3, minimum 2.04±0.87) and high-ratio seawater habitat (Sr/Ca>7, maximum 7.81±0.91). Thus, the habitat history types of C. mystus could be divided into four types:freshwater-estuarine brackish water type, estuarine brackish water settlement type, estuarine brackish water-seawater type, and freshwater-estuarine brackish water-seawater type. There were freshwater and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type, estuarine brackish water-seawater type, and freshwater-estuary brackish water-seawater type in the adjacent sea area of the Yangtze Estuary. There were sea water and estuarine brackish water hatching individuals whose habitat types included freshwater-estuarine brackish water type, estuarine brackish water settlement type, and freshwater-estuary brackish water-seawater type in the Chongming Island sea area of the Yangtze Estuary. This reflected the similarities and differences between the individuals in Chongming Island and the Lvsi sea area in the Yangtze Estuary. Through this study, it is proved for the first time that there are three incubation sites and four habitat types in the Yangtze Estuary and its adjacent sea area, which accurately reflect the diversity and complexity of the individual composition and life history of C. mystus.