Patterns of Distribution and Spatial Indicators of Ecosystem Change Based on Key Species in the Southern Benguela
Patterns of Distribution and Spatial Indicators of Ecosystem Change Based on Key Species in the Southern Benguela
复制标题
基于南本格拉主要物种的生态系统变化分布模式和空间指标
作者：
Katherine E Watermeyer;L. Hutchings;A. Jarre;L. Shannon
在过去几十年中，本格拉南部几个具有重要商业和生态价值的物种的分布经历了向南和向东的转移，最著名的是小型中上层鱼类沙丁鱼、沙丁鱼和凤尾鱼。了解这些变化及其影响对于对本格拉南部渔业采取生态系统办法并试图了解未来环境变化的潜在影响至关重要。为了研究这些转变在生态系统一级的可能影响，根据渔获量和调查数据，绘制了小型中上层鱼类转变之前(1985-1991年)、转变期间(1997-2000年)和转变后(2003-2008年)的14个关键物种的分布图，并用于计算空间指标，包括阿古拉斯角以东和以西的比例、生物量和面积的相对重叠、多样性指数、连接性。还比较了南海岸和西海岸的潜在相互作用。对于几个物种(红眼鱼、鳕鱼、金枪鱼、朱卡乌贼、黄尾鱼)，以前未查明的阿古勒斯角以东生物量比例的增加与小型中上层鱼类的增加是同一时期发生的，尽管没有达到同样的程度。平均而言，与小型中上层鱼类的重叠随着时间的推移而增加，总体系统连通性在中期最低，这可能表明系统正在转型。随着时间的推移，西海岸的连通性下降，而东海岸的连通性增加。随着时间的推移，其他物种的分布也发生了变化，阿古拉斯角以东的区域在潜在的营养相互作用方面变得越来越重要。生物量分布和结构复杂性的变化影响营养结构，从而影响系统的功能，在试图确定当前和未来系统一级变化可能对生态系统造成的影响时，应考虑其影响。
Several commercially and ecologically important species in the southern Benguela have undergone southward and eastward shifts in their distributions over previous decades, most notably the small pelagic fish sardine Sardinops sagax and anchovy Engraulis encrasicolus. Understanding these changes and their implications is essential in implementing an ecosystem approach to fisheries in the southern Benguela and attempting to appreciate the potential impacts of future environmental change. To investigate possible impacts of these shifts at an ecosystem level, distribution maps for before (1985–1991), during (1997–2000) and after (2003–2008) the shift in small pelagic fish were constructed for 14 key species from catch and survey data, and used to calculate spatial indicators including proportion east and west of Cape Agulhas, relative overlap in biomass and area, index of diversity, connectivity. Potential interactions on the south and west coasts were also compared. For several species (redeye; chub mackerel; kingklip; chokka squid; yellowtail), previously unidentified increases in the proportion of biomass east of Cape Agulhas were shown to have occurred over the same period as that of small pelagic fish, although none to the same degree. On average, overlap with small pelagic fish increased over time and overall system connectivity was lowest in the intermediate period, possibly indicating a system under transition. Connectivity declined over time on the west coast while increasing on the east coast. Distributions of other species have changed over time, with the region east of Cape Agulhas becoming increasingly important in terms of potential trophic interaction. Variations in distribution of biomass and structural complexity affect the trophic structure and hence functioning of the system, and implications should be considered when attempting to identify the possible ecosystem impacts of current and future system-level change.