School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.
Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, Seattle, WA, USA.
Glob Chang Biol. 2021 Jun;27(11):2328-2342. doi: 10.1111/gcb.15551. Epub 2021 Mar 22.
Anthropogenic climate change will impact nutrient cycles, primary production, and ecosystem structure in the world's oceans, although considerable uncertainty exists regarding the magnitude and spatial variability of these changes. Understanding how regional-scale ocean conditions control nutrient availability and ultimately nutrient assimilation into food webs will inform how marine resources will change in response to climate. To evaluate how ocean conditions influence the assimilation of nitrogen and carbon into coastal marine food webs, we applied a novel dimension reduction analysis to a century of newly acquired molecular isotope data derived from historic harbor seal bone specimens. By measuring bulk δ C and δ N values of source amino acids of these top predators from 1928 to 2014, we derive indices of primary production and nitrogen resources that are assimilated into food webs. We determined coastal food webs responded to climate regimes, coastal upwelling, and freshwater discharge, yet the strength of responses to individual drivers varied across the northeast Pacific. Indices of primary production and nitrogen availability in the Gulf of Alaska were dependent on regional climate indices (i.e., North Pacific Gyre Oscillation) and upwelling. In contrast, the coastal Washington and Salish Sea food webs were associated with local indices of freshwater discharge. For some regions (eastern Bering Sea, northern Gulf of Alaska) food web-assimilated production was coupled with nitrogen sources; however, other regions demonstrated no production-nitrogen coupling (Salish Sea). Temporal patterns of environmental indices and isotopic data from Washington state varied about the long-term mean with no directional trend. Data from the Gulf of Alaska, however, showed below average harbor seal δ C values and above average ocean conditions since 1975, indicating a change in primary production in recent decades. Altogether, these findings demonstrate stable isotope data can provide useful indices of nitrogen resources and phytoplankton dynamics specific to what is assimilated by food webs.
人为引起的气候变化将影响世界海洋的营养循环、初级生产力和生态系统结构，尽管这些变化的幅度和空间变异性存在相当大的不确定性。了解区域尺度海洋条件如何控制营养物质的可利用性，并最终将营养物质同化到食物网中，将有助于了解海洋资源将如何应对气候变化而发生变化。为了评估海洋条件如何影响氮和碳被同化到沿海海洋食物网中，我们应用了一种新的降维分析方法，对从历史悠久的港口海豹骨骼标本中获得的一个世纪的新分子同位素数据进行了分析。通过测量这些顶级捕食者在 1928 年至 2014 年间的源氨基酸的总 δC 和 δN 值，我们得出了反映初级生产力和氮资源同化到食物网中的指标。我们发现，沿海食物网对气候模式、沿海上升流和淡水排放做出了响应，然而，对个别驱动因素的响应强度在东北太平洋地区有所不同。阿拉斯加湾的初级生产力和氮可利用性指数取决于区域气候指数（即北太平洋环流振荡）和上升流。相比之下，华盛顿和萨利什海的沿海食物网与当地的淡水排放指数有关。对于一些地区（东白令海、北阿拉斯加湾），食物网同化的生产力与氮源有关；然而，其他地区没有表现出生产力与氮的耦合关系（萨利什海）。华盛顿州的环境指数和同位素数据的时间模式以长期平均值为中心波动，没有明显的趋势。然而，阿拉斯加湾的数据显示，自 1975 年以来，海豹的 δC 值低于平均值，海洋条件高于平均值，这表明最近几十年初级生产力发生了变化。总之，这些发现表明，稳定同位素数据可以提供有用的氮资源指标和特定于食物网同化的浮游植物动态指标。
