Nitrogen and Isotope Flows Through the Costa Rica Dome Upwelling Ecosystem: The Crucial Mesozooplankton Role in Export Flux
Nitrogen and Isotope Flows Through the Costa Rica Dome Upwelling Ecosystem: The Crucial Mesozooplankton Role in Export Flux
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DOI：
10.1029/2018gb005968
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发表时间：
2018-12
影响因子：
5.2
通讯作者：
M. Stukel;M. Décima;M. Landry;K. Selph
中科院分区：
文献类型：
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作者：
M. Stukel;M. Décima;M. Landry;K. Selph
哥斯达黎加穹顶(CRD)是一个公海上升流生态系统，浮游微藻(特别是聚球藻)、中浮游动物生物量高，营养水平高。为了阐明在这个独特的生态系统中支持营养结构和碳输出的食物网路径，我们使用马尔科夫链蒙特卡罗技术将来自四个独立实现的δ15N和浮游生物速率的数据同化到稳态、多室生态系统箱模型(线性逆模型)中。模型结果提供了生态系统氮和稳定同位素通量的良好约束快照。新的产量是由上升的硝酸盐支持的，而不是固氮。原生动物(而不是食草动物)是中游动物最重要的摄食方式，它们严重依赖于微型浮游动物的猎物。中游动物在垂直氮出口中发挥核心作用，主要是通过主动运输表层消耗的氮和深层排泄的氮，平均占总出口的36%-46%。碎屑或聚集摄食也是中游动物获取资源和在真光层内再生营养物质的重要方式。因此，在CRD中，被动下沉颗粒输出与浮游植物产量的比率非常低。与附近赤道太平洋数据约束的类似模型的比较表明，垂直迁徙对生物泵的主导作用是CRD的一个独特特征。然而，尽管原生动物是浮游植物的主要捕食者，但这两个地区都显示出从中游动物到较高营养水平的有效转移(如预期的那样，在鱼类、鲸目动物和海鸟种群较多的地区)。
The Costa Rica Dome (CRD) is an open‐ocean upwelling ecosystem, with high biomasses of picophytoplankton (especially Synechococcus), mesozooplankton, and higher trophic levels. To elucidate the food web pathways supporting the trophic structure and carbon export in this unique ecosystem, we used Markov Chain Monte Carlo techniques to assimilate data from four independent realizations of δ15N and planktonic rate measurements from the CRD into steady state, multicompartment ecosystem box models (linear inverse models). Model results present well‐constrained snapshots of ecosystem nitrogen and stable isotope fluxes. New production is supported by upwelled nitrate, not nitrogen fixation. Protistivory (rather than herbivory) was the most important feeding mode for mesozooplankton, which rely heavily on microzooplankton prey. Mesozooplankton play a central role in vertical nitrogen export, primarily through active transport of nitrogen consumed in the surface layer and excreted at depth, which comprised an average 36–46% of total export. Detritus or aggregate feeding is also an important mode of resource acquisition by mesozooplankton and regeneration of nutrients within the euphotic zone. As a consequence, the ratio of passively sinking particle export to phytoplankton production is very low in the CRD. Comparisons to similar models constrained with data from the nearby equatorial Pacific demonstrate that the dominant role of vertical migrators to the biological pump is a unique feature of the CRD. However, both regions show efficient nitrogen transfer from mesozooplankton to higher trophic levels (as expected for regions with large fish, cetacean, and seabird populations) despite the dominance of protists as major grazers of phytoplankton.