Damming, lost connectivity and the historical role of anadromous fish in freshwater ecosystem dynamics

Recent research has demonstrated the important role that high-biomass species play in the transfer of energy and nutrients across habitat boundaries, as well as the ecosystem consequences of their loss. To contrast the historical and current biomass of historically abundant anadromous forage fish, we combined historical records of habitat loss from damming with contemporary freshwater productivity of alewives and diet data of freshwater predator fish. Significant declines in production occurred by 1850 in the northeastern United States, long before any direct abundance data were available, which would have had significant effects on freshwater prey resources for the numerous predators directly affected by the transfer of nutrients across the freshwater–marine nexus. Current freshwater systems operate at approximately 6.7% of historical capacity of anadromous alewife biomass and abundance. This provides an example of habitat-mediated changes in connectivity limiting nutrient flux and energy flow among populations and species that alter ecosystem function at multiple scales.

近期研究已证实，高生物量物种在跨生境边界的能量与营养盐传递过程中发挥着关键作用，同时明确了其种群消失对生态系统造成的连锁影响。为对比历史上曾大量存续的溯河洄游饵料鱼类（anadromous forage fish）的历史与当前生物量水平，本研究整合了大坝营建导致的生境丧失历史记录、当前美洲西鲱（alewife）的淡水种群生产力数据，以及淡水捕食性鱼类的食谱数据。美国东北部的美洲西鲱种群生产力早在1850年就已出现显著下降，彼时尚未有可获取的直接种群丰度数据——这一变化会对众多捕食者的淡水猎物资源造成显著影响，而这些捕食者正直接受到淡水-海洋交汇带营养盐传递过程的作用。当前淡水生态系统中的溯河洄游美洲西鲱生物量与种群丰度，仅约为历史水平的6.7%。本研究案例揭示了生境介导的连通性变化如何限制种群与物种间的营养盐通量与能量流动，进而在多个尺度上改变生态系统功能。