Center for Watershed Sciences, University of California, Davis, CA, United States of America.
Department of Wildlife, Fish & Conservation Biology, University of California, Davis, CA, United States of America.
PLoS One. 2021 Oct 28;16(10):e0257444. doi: 10.1371/journal.pone.0257444. eCollection 2021.
Floodplains represent critical nursery habitats for a variety of fish species due to their highly productive food webs, yet few tools exist to quantify the extent to which these habitats contribute to ecosystem-level production. Here we conducted a large-scale field experiment to characterize differences in food web composition and stable isotopes (δ¹³C, δ¹⁵N, δ³⁴S) for salmon rearing on a large floodplain and adjacent river in the Central Valley, California, USA. The study covered variable hydrologic conditions including flooding (1999, 2017), average (2016), and drought (2012-2015). In addition, we determined incorporation rates and tissue fractionation between prey and muscle from fish held in enclosed locations (experimental fields, cages) at weekly intervals. Finally, we measured δ³⁴S in otoliths to test if these archival biominerals could be used to reconstruct floodplain use. Floodplain-reared salmon had a different diet composition and lower δ13C and δ³⁴S (δ¹³C = -33.02±2.66‰, δ³⁴S = -3.47±2.28‰; mean±1SD) compared to fish in the adjacent river (δ¹³C = -28.37±1.84‰, δ³⁴S = +2.23±2.25‰). These isotopic differences between habitats persisted across years of extreme droughts and floods. Despite the different diet composition, δ¹⁵N values from prey items on the floodplain (δ¹⁵N = 7.19±1.22‰) and river (δ¹⁵N = 7.25±1.46‰) were similar, suggesting similar trophic levels. The food web differences in δ13C and δ³⁴S between habitats were also reflected in salmon muscle tissue, reaching equilibrium between 24-30 days (2014, δ¹³C = -30.74±0.73‰, δ³⁴S = -4.6±0.68‰; 2016, δ¹³C = -34.74 ±0.49‰, δ³⁴S = -5.18±0.46‰). δ³⁴S measured in sequential growth bands in otoliths recorded a weekly time-series of shifting diet inputs, with the outermost layers recording time spent on the floodplain (δ³⁴S = -5.60±0.16‰) and river (δ³⁴S = 3.73±0.98‰). Our results suggest that δ¹³C and δ³⁴S can be used to differentiate floodplain and river rearing habitats used by native fishes, such as Chinook Salmon, across different hydrologic conditions and tissues. Together these stable isotope analyses provide a toolset to quantify the role of floodplains as fish habitats.
洪泛区是各种鱼类的重要育雏栖息地，因为它们拥有高度多产的食物网，但目前几乎没有工具可以量化这些栖息地对生态系统水平生产的贡献程度。在这里，我们进行了一项大规模的野外实验，以描述在美国加利福尼亚州中央谷的一个大型洪泛区和相邻河流上饲养鲑鱼的食物网组成和稳定同位素（δ¹³C、δ¹⁵N、δ³⁴S）的差异。该研究涵盖了不同的水文条件，包括洪水（1999 年、2017 年）、平均（2016 年）和干旱（2012-2015 年）。此外，我们还在每周间隔的封闭地点（实验场、笼子）中饲养鱼类，以确定猎物和肌肉之间的同化率和组织分馏。最后，我们测量了耳石中的 δ³⁴S，以测试这些档案生物矿物是否可用于重建洪泛区的使用情况。在相邻河流中饲养的鲑鱼的饮食组成和 δ¹³C 和 δ³⁴S 较低（δ¹³C = -33.02±2.66‰，δ³⁴S = -3.47±2.28‰；平均值±1SD）与河流中的鱼类（δ¹³C = -28.37±1.84‰，δ³⁴S = +2.23±2.25‰）相比。这些栖息地之间的同位素差异在经历多年极端干旱和洪水的情况下仍然存在。尽管饮食组成不同，但洪泛区上猎物的 δ¹⁵N 值（δ¹⁵N = 7.19±1.22‰）和河流（δ¹⁵N = 7.25±1.46‰）相似，表明相似的营养水平。栖息地之间食物网 δ13C 和 δ³⁴S 的差异也反映在鲑鱼肌肉组织中，在 24-30 天内达到平衡（2014 年，δ¹³C = -30.74±0.73‰，δ³⁴S = -4.6±0.68‰；2016 年，δ¹³C = -34.74 ±0.49‰，δ³⁴S = -5.18±0.46‰）。耳石中连续生长带测量的 δ³⁴S 记录了一个每周的饮食输入变化时间序列，最外层记录了在洪泛区（δ³⁴S = -5.60±0.16‰）和河流（δ³⁴S = 3.73±0.98‰）上度过的时间。我们的结果表明，δ¹³C 和 δ³⁴S 可用于区分在不同水文条件和组织中使用的本地鱼类（如奇努克鲑鱼）的洪泛区和河流饲养栖息地。这些稳定同位素分析共同提供了一种工具集，可用于量化洪泛区作为鱼类栖息地的作用。
