Dataisotopes from Small birds, big effects: the little auk (Alle alle) transforms high Arctic ecosystems

In some arctic areas, marine-derived nutrients (MDN) resulting from fish migrations fuel freshwater and terrestrial ecosystems, increasing primary production and biodiversity. Less is known, however, about the role of seabird-MDN in shaping ecosystems. Here, we examine how the most abundant seabird in the North Atlantic, the little auk (Alle alle), alters freshwater and terrestrial ecosystems around the North Water Polynya (NOW) in Greenland. We compare stable isotope ratios (δ15N and δ13C) of freshwater and terrestrial biota, terrestrial vegetation indices and physical–chemical properties, productivity and community structure of fresh waters in catchments with and without little auk colonies. The presence of colonies profoundly alters freshwater and terrestrial ecosystems by providing nutrients and massively enhancing primary production. Based on elevated δ15N in MDN, we estimate that MDN fuels more than 85% of terrestrial and aquatic biomass in bird influenced systems. Furthermore, by using different proxies of bird impact (colony distance, algal δ15N) it is possible to identify a gradient in ecosystem response to increasing bird impact. Little auk impact acidifies the freshwater systems, reducing taxonomic richness of macroinvertebrates and truncating food webs. These results demonstrate that the little auk acts as an ecosystem engineer, transforming ecosystems across a vast region of Northwest Greenland.

在部分北极区域，鱼类洄游所产生的海洋源营养盐（marine-derived nutrients, MDN）可滋养淡水与陆地生态系统，提升初级生产力与生物多样性。然而，学界对于海鸟介导的海洋源营养盐在生态系统塑造中的作用仍所知甚少。
本研究聚焦北大西洋最为丰富的海鸟——小海雀（Alle alle），对格陵兰岛北冰间湖（North Water Polynya, NOW）周边淡水与陆地生态系统的改造作用。我们对比了存在与缺失小海雀群落的汇水区中，淡水与陆地生物的稳定同位素比值（δ¹⁵N与δ¹³C）、陆地植被指数，以及淡水生态系统的理化性质、生产力与群落结构。
小海雀群落的存在会通过输入营养盐并大幅提升初级生产力，深刻改变淡水与陆地生态系统。基于海洋源营养盐中升高的δ¹⁵N信号，本研究估算得出：在受海鸟影响的生态系统中，海洋源营养盐支撑了超过85%的陆地与水生生物量。此外，通过采用不同的海鸟影响替代指标（群落距离、藻类δ¹⁵N），可识别出生态系统响应海鸟影响强度递增的梯度变化。
小海雀的活动会使淡水系统酸化，降低大型无脊椎动物的分类丰富度并简化食物网。上述结果表明，小海雀作为生态系统工程师，改造了格陵兰西北部广袤区域内的生态系统。