海洋生态与环境科学重点实验室知识库

摘 要

       本研究以长江口及其邻近海域重要无脊椎动物—三疣梭子蟹为研究对象，依 据长江口渔业资源监测数据和调查数据探究其资源时空变动特征，分析其资源变 动影响因素，依据 LBB 方法对长江口三疣梭子蟹群体生物资源进行有效评估， 依据分子生态学研究方法探讨长江口三疣梭子蟹群体遗传结构，解析增殖放流是 否影响其遗传多样性，研究成果将为科学合理的规划开发利用三疣梭子蟹的生物 资源和实施生态修复提供理论基础和科学依据。研究结果如下： （1）全国及长江口附近海域三疣梭子蟹历年捕捞产量数据结果显示：过去 三十余年，三疣梭子蟹捕捞产量快速增长，捕捞压力逐年升高。三疣梭子蟹历年 捕捞产量年际波动显著，各地均在 2014 年达到最大渔获产量，2014 年至 2020 年国内三疣梭子蟹渔获产量显著下滑。长江口及其邻近海域梭子蟹产量稳定占据 全国产量的 50%左右，其中浙江近海的捕捞量又占该调查海域的一半以上，江苏 省梭子蟹捕捞量占比略低且年际变化不太显著，上海市捕捞产量在调查海区的占 比长期低于 10%，且有持续走低的趋势。2003 年起全国梭子蟹养殖产量显著升 高，并于 2016 年达到最高值，之后五年出现持续的小幅回落。梭子蟹养殖产量 远低于同期捕捞产量，是后者的有益补充，也为后续资源修复提供了可能。自 2003 年以来，作为梭子蟹传统产区的浙江近海，虽然其单位面积养殖产量远高 于长江口及全国水平（P＜0.01），但随着养殖面积的逐渐缩小，浙江省海水养 殖产量在长江口海区及全国的份额持续下跌，且已逐渐被江苏省赶超。 （2）依据 1998 年至 2018 年 10 个春季航次和 12 个秋季航次长江口及其邻 近海域三疣梭子蟹野外调查数据，分析其生物量及丰度时空分布特征。研究结果 显示，长江口春秋两季该海域三疣梭子蟹资源密度年际波动显著。春季生物量和 丰度的最大值出现在 2014 年，分别为 84.71±33.86kg/km2 及 2.66±2.86kN/km2， 最小值出现在 2018 年，分别为 0.47±0.67kg/km2 和 0.02±0.04 kN/km2，年际间存 在显著性差异（P＜0.01）；长江口三疣梭子蟹秋季生物量和丰度的峰值出现在 2013 年 11 月，达到 512.73±115.34kg/km2 及 9.40±2.83kN/km2，最低值出现在 2003 年，分别为 11.30±5.96 kg/km2 及 0.05±0.03kN/km2，年际波动较为剧烈且差异显 著（P＜0.01）。2000 年左右，长江口及其邻近海域三疣梭子蟹资源较上世纪 90 年代出现明显的衰退，在该水域几近绝迹，其生物量常年维持在低位；经过 2010 年至2014年的快速恢复之后再次出现锐减，至2018年达到最低点后有小幅反弹， 总体变化与全国和长江口渔业产量变化趋势一致。空间分布分析结果显示，春季 和秋季调查海域南部三疣梭子蟹资源量低于北部，这可能与其越冬洄游、生殖洄游活动以及栖息水域南部外海存在的高温高盐水团相关。群体生物学特征分析表 明，2014 年后该海域三疣梭子蟹出现明显的小型化趋势。 （3）依据三疣梭子蟹群体生物特征数据，包括三疣梭子蟹胸甲宽度及在各 个宽度范围内个体的分布频率等，运用 LBB 模型评估三疣梭子蟹渔业资源开发 利用情况，首次将 LBB 法应用于无脊椎动物群体资源评估。研究结果显示，捕 捞死亡率/自然死亡率（F/M）（1.79）、捕捞死亡率/生长速率（F/K）（2.61） 的比值均大于 1，表明在目前的捕捞压力下，三疣梭子蟹的自然繁殖能力不足以 保障群体的可持续发展。平均宽度/最佳宽度（Wmean/Wopt）=0.89，开捕宽度/最佳 开捕宽度（Wc/Wc_opt）= 0.72，表示当前的开捕宽度和渔获物的平均甲宽都要小 于理想值，三疣梭子蟹处于过度捕捞的状态中。95%体宽/渐进体宽（W95th/Winf）、 现存生物量/初始生物量（B/B0）和现存生物量/可产生最大可持续产量的生物量 （B/BMSY）分别为 0.91、0.18 和 0.50，证实三疣梭子蟹的生物资源在目前的捕捞 压力下面临衰退甚至枯竭的危险。 （4）依据 2013 年至 2017 年长江口渔业资源和环境调查数据，解析三疣梭 子蟹群体分布与环境因子的关系。结果显示，总氮、温度、深度、盐度和溶解氧 影响春季长江口及其邻近海域三疣梭子蟹生物量及丰度分布，总氮和溶解氧制约 秋季长江口及其邻近海域三疣梭子蟹生物量及丰度分布，盐度、总氮、深度和总 磷驱动 2018 年长江口及其邻近海域三疣梭子蟹生物量与丰度季节内分布。 （5）长江口海域三疣梭子蟹系统发育分析结果显示，对比 2019 年长江口海 域三疣梭子蟹二代测序与日本学者一代测序结果，分析显示二者 mtDNA 基因组 序列具有 99.56%的一致性，表明长江口区域三疣梭子蟹与日本近海标本具有相 同的进化地位。 （6）通过微卫星技术物解析三疣梭子蟹野外捕获群体和增殖放流群体遗传 多样性差异，样本来自长江口及其邻近海域的 13 个调查站位和 2019 年参加当年 增殖放流任务的南通、舟山两地人工养殖厂，共计 15 个三疣梭子蟹群体的 225 个样本完成了测序分析。结果显示：15 个群体的个体虽然均具有较高的遗传多 样性水平，部分群体间存在中等程度的遗传分化，多数群体间遗传分化不明显， 且普遍存在近交现象；系统发育及 Structure 分析表明：13 个三疣梭子蟹野生群 体及 2 个增殖放流群体可分为沿经度线分布的 4 个亚群，除部分亚群存在一定程 度的遗传分化外，多数亚群间存在广泛的基因交流，遗传距离较小，不存在明显 的系统发育分化；Bottleneck 分析显示除采样量较低的 14 号站位外，其他群体均 未出现遗传瓶颈效应。研究结果证实，长江口增殖放流群体对野生群体的遗传多 样性水平未产生显著影响。

Abstract

This study focused on the Portunus trituberculatus, which is the most important invertebrate economic species in the Yangtze River Estuary and its adjacent waters. We searched for the spatio-temporal variation characteristics of its resources from the fishery survey data and monitoring data over the past decades, and analyzed the factors affecting its resources changes. We evaluated the biological resources of population of Portunus trituberculatus in the Yangtze River Estuary effectively based on the LBB method. The genetic structure of populations of P. trituberculatus in the Yangtze River Estuary was analyzed according to the research methods of molecular ecology to explore the impacts of stock enhancement and releasing on the genetic diversity of swimming crabs. The research results will provide theoretical and scientific basis for planning, development and utilization of biological resources of Portunus trituberculatus and implementation of ecological restoration. The research results are as follows: （1）By analyzing the annual data of marine fishing output, we found that: Over the past 30 years, the P.trituberculatus from national sea area and the waters surrounding the Yangtze Estuary had faced severe fishing pressure, with rapid growth in fishing yields and significant inter-annual fluctuations. The maximum fishing output came out in 2014 in the surveyed waters. From 2014 to 2020, the yield of P.trituberculatus decreased significantly. The output of swimming crabs in the Yangtze Estuary accounts for about 50% of the national output, while the fishing yields in the coastal waters of Zhejiang accounts for more than half of the surveyed area. In Jiangsu Province, the proportion of crab fishing was slightly lower and the inter-annual variation was not so significant. In Shanghai, the proportion was less than 10% with a trend of continuous decline. From 2003, there was a significant increase in the national production of the swimming crab in mariculture, and it reached the highest production in 2016, then fell slightly in the following five years. The yield of crab cultured in mariculture was much lower than that caught from the sea at the same period, which is a beneficial supplement to the latter and also provides the possibility for resource restoration. As the traditional producing area of the crab, although the yield per unit area of Zhejiang Province was much higher than that of the Yangtze Estuary and the national level (P< 0.01), with the gradual reduction of its breeding area, the share of its mariculture yield in the Yangtze Estuary and in the nations continued to decline, and it had been gradually overtaken by Jiangsu Province. （ 2 ） The spatio-temporal distribution characteristics of its biomass and abundance of P.trituberculatus were analyzed in the Yangtze River Estuary and its adjacent waters based on survey data of 10 voyages in spring and 12 in autumn from 1998 to 2018. The results showed that the annual fluctuation of the resources was significant. The maximum biomass and abundance in spring appeared in 2014, which were 84.71±33.86 kg/km2 and 2.66±2.86 kN/km2 , respectively. While the minimum biomass and abundance appeared in 2018 and the corresponding values were 0.47±0.67 kg/km2 and 0.02±0.04 kN/km2 , with significant differences among years(P<0.01). The maximum biomass and abundance of swimming crabs in autumn were 512.73±115.34 kg/km2 and 9.40±2.83 kN/km2 in November 2013, however, the lowest values were respectively 11.30±5.96 kg/km2 and 0.05±0.03 kN/km2 in 2003. The inter-annual fluctuations were fiercely, meanwhile, differences between the maximum and minimum values were significant (P<0.01). In the early 21st century, compared with the 1990s, the resources of P.trituberculatus in the Yangtze Estuary showed obviously decline and almost extinct in the waters. Its biomass remained at a low level all the years round, and after a rapid recovery from 2010 to 2014, it sharply decreased again, reaching the lowest point in 2018 and then recovering slightly， whereas the trend was consistent with fishery statistic data of national and the Yangtze Estuary. In most years, the resources of P.trituberculatus captured from southern sampling locations were lower than those of the northern sites in spring and autumn, which may be related to the overwintering and reproductive migration of the crab and the presence of water masses with high temperature and high salinity in the southern offshore waters of the habitat area. Studies on biological characteristics of the populations showed that after 2014, Portunus trituberculatus in the sea area showed a significant trend of miniaturization. （3）In this study, LBB analysis was firstly applied to the evaluation of invertebrate population resources. By measuring the width of the carapace of P.trituberculatus and the distribution frequency of individuals in each width range, the current situation of development and utilization of the fishery germplasm resources for swimming crab was evaluated: The ratios of F/M (1.79) and F/K (2.61) were both greater than 1, indicating natural reproduction capacity of the crab was not enough to guarantee the sustainable development of its population under current fishing pressure. Wmean/Wopt=0.89 and Wc/Wc_opt= 0.72，meant that carapace width at first fishing and average carapace width of the catch were both less than ideal value, and the crab was overfished. W95th/Winf (0.91), B/B0 (0.18) and B/BMSY (0.50) indicated that the biological resources of the P.trituberculatus were facing the risk of decline or even depletion under current fishing pressure. （4）The relationship between the distribution of Portunus trituberculatus and environmental factors were analyzed based on the survey data of fishery resources and environment in the Yangtze River Estuary from 2013 to 2017. The results showed total nitrogen, temperature, depth, salinity and dissolved oxygen were the main environmental factors affecting the biomass and abundance of P.trituberculatus in spring. However, total nitrogen and dissolved oxygen restricted the distribution of the biomass and abundance of the swimming crab in the Yangtze Estuary in autumn. Salinity, total nitrogen, depth and total phosphorus were the driving factors for the seasonal distribution of Portunus trituberculatus in this sea area in 2018. （5）In 2003, Yamauchi et al. conducted Sanger sequencing on the full length of mitochondrial DNA of P.trituberculatus collected from Tokyo waters. In this study, Next-Generation Sequencing was carried out on the samples collected from the Yangtze Estuary in 2019. 99.56% of the two mitochondrial DNA sequences were identical by nucleotide alignment, indicating that the swimming crabs caught from the Yangtze Estuary and coastal waters of Japan share the identical evolutionary status. （6）6 pairs of microsatellite primers were used to conduct sequencing analysis on 225 samples from 15 populations of P.trituberculatus, which including specimens from 13 survey locations in the Yangtze Estuary and 2 artificial breeding plants in Nantong and Zhoushan participated in the stock enhancement and releasing of that year in 2019. The results were as follows: Although the individuals of the 15 populations had a good level of genetic diversity，moderate genetic differentiation had been found between some populations. Inbreeding was common and serious among them. The phylogenetic and genetic structure analysis showed that 13 wild populations and 2 stock enhancement and releasing populations could be divided into 4 subpopulations distributed along the longitude line. Except for some sub populations with moderate genetic differentiation, most sub populations have extensive gene exchange, small genetic distance, and no obvious topological isomerism. Bottleneck analysis showed that other populations did not suffer genetic bottleneck effect except for locility No. 14, which had a low sampling volume. In 2019, a large number of individuals released from the two artificial breeding plants in Nantong and Zhoushan did not reduce the genetic diversity of the wild population in Yangtze Estuary and its adjacent sea area.