【作者】 李云凯；

【导师】 陈立侨；

【作者基本信息】 华东师范大学 ， 水生生物学， 2009， 博士

【摘要】 东海海区作为我国第二大海区,渔业资源丰富,是沿近海重要的渔区。2000年东海海洋捕捞产量达625.4×10~4 t,占全国海洋捕捞产量的42.33%。随着沿海经济的快速发展,各类陆源污染物排放量迅猛增加,东海海洋受污染的态势日益加剧。加之长期以来中国在东海的捕捞力量持续增长,东海底层主要经济鱼类资源显著衰退,渔获物日趋小型化,生命周期短、低营养级渔获物比例增加,渔业资源正在向低值、恶劣转化,资源状况令人担忧。沿岸与近海资源在充分或过度利用下仍处在衰退中,上层鱼类、头足类、小宗经济鱼类资源等潜力已经不足,小型鱼、小虾和杂蟹资源数量虽多,但利用价值不高。东海渔业正处在低值鱼、低龄鱼和小型鱼渔获量居高不下的高产假象中,而实际上海洋生物资源状况在继续恶化。然而,有关东海大陆架污染治理和渔业管理的工作尚未在“生态系统的架构”下统一开展,渔业生产仍然着眼于短期利益,捕捞结构不合理,捕捞强度控制不力,过度捕捞和养殖仍然在加速破坏东海大陆架生态系统的正常结构。为探讨东海大陆架生态健康恶化的成因,解决其环境污染和渔业资源衰退的问题,有关科研单位对东海大陆架的环境、生态、渔业和生物资源等,进行了多次大规模的调查和长期的监测统计工作,相继开展了许多相关的研究,积累了相当全面、系统的基础资料。但是,以往的研究大多只针对生态系统中一种或几种环境和生物因子,未能充分整合有关东海大陆架完备的基础数据和资料。采用基于食物网的生态系统模型,从整个系统的角度,并采用量化的方法来探讨渔业和环境影响的研究在国内尚不多见。本论文运用生态学、水生生物学、生态经济学并紧密结合渔业生态系统模型分析方法的国际前沿和我国的海洋渔业管理中的关键问题和迫切需求进行了系统的分析,得出了可量化和综合的结果,对东海大陆架的渔业和环境决策也具有一定的指导意义。从生态系统发育的角度,指出“幼态化”是东海大陆架生态系统结构的现状特征,其发育的过程是由“成熟态”向“幼态”逆向演替;对东海大陆架生态系统的发育进行了动态模拟,得出了与其发育进程相一致的结果。在对东海大陆架生态系统各功能组以及渔业之间的相互关系进行量化分析的基础上,对相关捕捞结构调整进行了动态模拟,提出了在保护和恢复生态系统正常功能结构的同时,兼顾渔业经济收益和社会效益最佳化的捕捞结构比例;根据生态系统资源保护的关键种理论,首次应用生态系统模型对东海大陆架生态系统的关键种进行了筛选。本文的具体结果及结论如下:1.东海大陆架生态系统结构和功能的Ecopath模型分析应用因子分析聚类分析,构建了一个具有38个功能组的东海大陆架生态系统的能量平衡模型,同时整合6种捕捞方式,并利用其基本分析和网络分析(Network analysis)功能,对1998～2001年间东海大陆架生态系统的结构和特征进行了量化和系统的研究。整个东海大陆架生态系统主要由7个整合营养级构成。其能流、生物量及生产量的分布呈金字塔型,能量流动主要发生在食物网底层部分,营养级Ⅰ的利用效率低下,大量初级生产力未进入更高层次的营养流动,从而造成生态系统营养流动的“阻塞”。主要经济鱼类功能组较高的渔业捕捞死亡率和生态转化效率,表明各功能组生物的渔业捕捞压力较大。混合营养影响(Mixed trophic impacts)研究表明,渔业对整个生态系统的负面影响显著,渔获物平均营养级(Mean trophic level of the catch)从1965年的3.5下降到2001年的3.01,尽管捕捞量不断提高,但来自低营养级的生物比例不断增加,渔获物低质化、小型化严重。过高的净初级生产力(NPP)、初级生产力/呼吸(TPP/R)以及较低的联结指数(CI)、系统杂食指数(SOI)和Finn’s循环指数(FCI)等生态系统参数,则表明东海大陆架生态系统的健康度较差、成熟度和稳定性较低,是一个典型的尚处于“幼态”的生态系统。2.东海大陆架生态系统发育的Ecopath比较研究采用Ecopath构建了东海大陆架1970(1969～1972)和2000(1998～2001)年代的生态系统模型。比较了这2个模型在基本生态参数、系统总体特征、食物网关系以及营养流的分布和循环等方面的差异。模型参数估计表明,东海生态系统结构正由底层系统向中上层系统转变,底层鱼类尤其是大型肉食性鱼类的生物量和流量呈现下降趋势,而中上层小型鱼虾类生物量和流量则显著上升。值得注意的是,水母类的生物量增加了近150%。各种鱼虾类的P/B系数以及捕捞死亡占鱼虾类生产量的比例均显著上升,表明捕捞的压力有日益增强的趋势。初级生产力、总生物量以及系统总输出均显著上升。渔获物平均营养级由1970年代的3.14下降到3.01,在表征生态系统“成熟度”的各项指标中,NPP、NPP/R、ascendency在模拟的两个年代之间急剧增加,而CI、SOI、FCI等指标则显著下降,因沉积而脱离系统的碎屑量增长了8%,食物链路径总数和平均长度也大幅度降低,表明食物网之间的联系减少。此外,营养级Ⅳ、Ⅴ的生物量、生产量以及流量所占的比例显著减小,而营养级Ⅰ、Ⅱ、Ⅲ所占的比例则不断增大。上述指标的变化,恰恰与生态系统的正常发育进程相反,提示东海大陆架生态系统在这30年间的发育过程由成熟态向幼态发生了逆向演替。3东海大陆架生态系统发育和渔业影响的Ecosim动态模拟以1970年代的Ecopath模型作为初始状态,采用Ecosim对东海大陆架生态系统在1969～2000年间的发育动态进行了时间序列分析模拟。结果表明,在捕捞强度的时间强制序列的驱动下,大中型鱼类的生物量均显著下降,小型鱼虾类的生物量和捕捞量则显著上升。大部分鱼虾类捕捞量的模拟结果与统计值吻合较好,并给出了合理的预测趋势。系统总流量和初级生产力急剧增加,终末状态由碎屑沉积而脱离系统的物流增加26%。TPP/R增加了85.9%,FCI和FMPL分别下降了53.1%和14.9%,系统的成熟度显著降低,其预测趋势与东海大陆架生态系统的发育进程相符合。Ecosim的模拟结果较好地解释了东海大陆架生态系统的发育机制,即在不断增强的渔业捕捞压力下,大中型鱼类尤其是顶级捕食者的资源量更易遭到破坏,从而减少了对小型鱼虾类的捕食压力,使得这些r型种取代k型种占据系统的统治地位,这也很好的解释了渔获物中小型鱼虾类比例增加的现状。4.东海大陆架渔业政策的Ecosim模型分析系统的构建以2000年代的Ecopath模型为“核心”,输入时间序列模拟得出动态模拟关键参数vulnerability,应用Ecosim动态模拟建立了目前东海大陆架海区渔业政策模拟系统。通过此系统调节渔业捕捞结构比例,可以模拟分析在经济效益、社会效益和生态效益目标下,系统收入支出、生态系统的结构和功能的变化,从而筛选出最佳渔业捕捞政策。系统模拟输出结果显示,为了最大限度的提高经济效益和社会效益,生态系统受增加的渔业捕捞强的影响显著,系统中各主要功能组的生物量显著降低,生态系统多样性指数、系统成熟度,渔获物平均捕捞营养级显著降低。而单独以生态效益为发展目标时,整个渔业捕捞努力量降低70%,这将会导致严重的经济和社会问题的出现。系统权衡分析表明,对目前东海捕捞结构而言,严格控制捕捞结构比例,可以达到经济增长、社会稳定和保护生态环境的三赢局面。5.东海大陆架生态系统关键种的筛选的研究关键种可以为了最大程度地保护生物多样性而进行优先保护的目标,然而传统的“移除实验”方法在实验室条件下对生态系统中关键种的确定不是一件容易的事情。本节应用Ecopath with Ecosim模型的动态模拟功能,阐述了应用动态模型分析筛选生态系统关键种的全新方法。并以东海大陆架海洋生态系统为例,应用Ecosim动态模拟传统的“移除实验”方法通过4个传统生态学关键种确定指标(community importance,community longevity support,interaction strength index和keystoneness index)对系统关键种进行确定。海龟(Marine turtles)和海鸟(Seabirds)功能组被确定了目前东海大陆架生态系统的关键种,并分析了他们在东海生态系统中的调控作用。应用生态系统模型动态模拟分析功能,将有助于简化传统生态系统关键种的筛选方法并为海洋生态系统资源保护政策的制定提供理论指导。更多还原

【Abstract】 As China’s second-largest large marine ecosystem, the East China Sea Shelf has suffered from overfishing, eutrophication and physical disturbance over several decades. The East China Sea Shelf (ECSS) is also the China’s most productive and has provided valuable fisheries to coastal communities and regional countries (China, Japan, and Korea) for centuries. In the last 50 years, the ECSS has been heavily exploited, and developments in its commercial fisheries have shifted the exploitative focus from top predators in the ecosystem to more abundant species at lower trophic levels. We observed several signs that such "fishing down the food web" has occurred in the ECSS through prolonged and intensive fishing pressure over this 50-year period. As an overall indicator of fishery impacts on the system, biodiversity declined significantly. At the same time, the composition of fishery landings became increasingly dominated by juveniles and relatively small, lower trophic level species with high turn-over rates. The mean trophic level of landings decreased from 3.5 in 1965 to 2.8 in 1990. Many demersal stocks are fully exploited or overexploited, and some pelagic stocks also show overexploitation trends, although some species are still producing high landings. However, despite these clear indications of ecosystem-level consequences arising from current fishing practices, little ecological modeling work has been done for the ECSS, and to date there is still no quantitative assessment of ecosystem dynamics for this region.To properly manage the fisheries resources of East China Sea and address fishery depletion, studies were undertaken on pollution, fishery and ecology. To support these studies, a large quantity of data was collected on fisheries statistics, population parameters, diet compositions, and physical and chemical variables. However, limited efforts were put into the development of an ecosystem-based fisheries resource management strategy. In this study Ecopath with Ecosim, an ecosystem modeling approach based on food-web, was employed to construct both the static and dynamic models and evaluate the ecosystem structures, functioning, keystone species, succession development and the impacts of fishing in ECSS ecosystem. The mechanism of fishery degradation was revealed. Moreover, the optimal strategies of balancing the economic, social and conservation objectives were discussed. The results and conclusions are described in detail as follows:1. Trophic model of the East China Sea Shelf: analysis of ecosystem structureA trophic mass-balance model of this ecosystem was developed in order to characterize the structure and functioning of its food web, quantify the ecological impacts of fishing that it sustained during the early 2000s. Using a multivariate statistical analysis, thirty-eight functional groups were identified, including fish and invertebrate groups targeted and not targeted by fisheries. Strong benthic-pelagic coupling was found present in this ecosystem. In particular, this study highlighted the inter-dependent relationships that exist among plankton, benthic invertebrates, and detritus. Recent fishing activities were characterized by high gross efficiencies and high exploitation rates for various commercially targeted and non-targeted species, leading to the consumption of much of the ecosystem’s fishable production. Overall, the findings give a better explanation of the current problems of eutrophication and fishing-induced evolution in the East China Sea Shelf and highlight the need for developing ecosystem-based fisheries management.2. Interdecadal changes in the East China Sea Shelf ecosystem: a comparison of the 1970s and 2000sI ecosystem models for two time periods (1969-1972 and 1998-2001) constructed and compared them with respect to basic ecological indices, overall system indices, food web and ecosystem structure, energy and nutrient cycling, and trophic flows. The results show that the ecosystem had changed from being dominated by demersal species to a heavily-exploited system dominated by pelagic species with a high turnover rate. Increases in the P/B ratios and fishing mortality levels observed for species groups reveal rapidly intensifying fishery stress over the three decades. Primary production, total biomass, and total throughput decreased throughout this period. Drawing upon Odum’s theory of ecosystem maturity, this study shows that the maturity and stability of the East China Sea Shelf ecosystem has decreased. The structured, web-like ecosystem of the 1970s developed into a less complex and the system’s maturity fell to its lowest observed level. During this period, the successional development of the system occurred in reverse.3. Evaluating ecosystem development stages and the impacts of fishing in the East China Sea Shelf using EcosimAn ecosystem model representing the continental shelf of the East China Sea was fitted to the available time series data from 1969 to 2000. A process-oriented model was used to explore the extent to which changes in marine reources and the ecosystem were driven by trophic interactions and fishing activities. Fishing effort was used to drive the model, while observed catches were compared with the predicted results. A reduction in the sum of the squared deviations of the observed and predicted value of the catch is used as a metric for calibrating and assessing the fit of the model. Trophodynamic indicators were used to explore the ecosystem’s structural and functional changes from 1969 to 2000. The model’s predictions match the catch of most functional groups and trophodynamic indicators suggest a degradation pattern over time: both the mean trophic level of community and a modified version of Kempton’s index of biodiversity decrease with time, while the total flow to detritus and the loss of production due to fishing increase from 1969 to 2000. Additionally, the demersal/pelagic ration decreases due to an overall increase in the abundance of pelagic fish in the ecosystem. Overfishing is blamed for the degradation of the ecosystem development.4. Evaluating ecosystem-based management strategies of the East China Sea Shelf with EcosimUnderstanding the trade-off relationships between economic, social and ecological objectives is important in designing policies to manage or restore ecosystems. As the most productive sea in China, East China Sea ecosystem supports various commercial, recreational, and artisanal fisheries. Many fisheries are now depleted or had experienced substantial decline in productivity. Ecopath with Ecosim was employed to evaluate how the ecosystem may respond to changes in fisheries activities over a period of 20 years and search for the optimal policy considering the economic, social, and ecological objectives. Four fishery management scenarios, which maximized three independent (fishery profits, employment and ecosystem structure) and the combination of the above three objectives were simulated with the vulnerability value estimated from the time-series simulation. Results suggested that socioeconomically driven policy caused the ecosystem to be vulnerable whereas maximized ecological stability and the composition scenarios. To maximize social and economical criteria, the ecosystem structure was shifted to a simplified state where the high trophic level species became depleted and the low trophic level species gained dominance in the landings with the lowest mean trophic level of catch of 2.66. When an ecosystem structure criterion was considered, the model predicted effort should decreases more than 70% for all fishing sectors. A trade-off analysis indicates that the ’best composition’ strategy would be optimal to balance fishery and conservation. This study highlights the conflict between maximizing conservation and social objectives, win-win solutions between conservation and economic objectives may be possible.5. A search for keystones in East China Sea Shelf, using a mass-continuity trophic modelKeystone species play a central role in shaping at least some marine communities in the sense that system-wide phase shifts can be mediated by the presence, absence, or the relative abundance of these key interactions. Identifying keystones is considered crucial for understanding the resilience of ecosystems to exogenous forces because non-linear, or catastrophic, community changes might hinge on the populations of one or a few species. Removal experiments are traditionally the most reliable approach for identifying keystone species, but such experiments can be accomplished only on small scales and with only a few types of species in any given system. I described the results of a series of simulated (functional group) removal experiments using a whole-system food web model of East China Sea Shelf for the period 1998-2001. Four indices were used to rank functional groups, based on the results of these simulated removal experiments: community importance, community longevity support, interaction strength index, and keystoneness index. Marine turtles produced the highest keystone index followed by Seabirds in the present iteration of the Ecopath model of East China Sea Shelf, which would be a good example for the conservational policy searching in the future in East China Sea Shelf ecosystem.更多还原