Center for Ecological Research, Kyoto University, 2-509-3, Hirano, Otsu, Shiga, 520-2113, Japan.
Faculty of Environmental Earth Science, Hokkaido University, N10W5, Sapporo, Hokkaido, 060-0810, Japan.
Oecologia. 2022 Feb;198(2):493-505. doi: 10.1007/s00442-022-05119-6. Epub 2022 Feb 14.
Animals affect element cycling in ecosystems by consumption and excretion. Amphidromous shrimps frequently dominate low-mid altitude streams, where downstream connectivity to oceans is sustained. Although shrimps' direct influence on benthic communities has been studied, little is known about their influences on nutrient cycling. Here, we hypothesized that the dominance of shrimps alters nutrient mineralization by benthic macroinvertebrates in streams due to the difference in the quality and quantity of excretion between shrimps and aquatic insects. We tested this hypothesis through a field manipulative experiment, excretion measurements of animals, and field surveys. In the field manipulative experiment, the presence of shrimps slightly decreased the biomass of aquatic insects but tripled total benthic macroinvertebrate biomass directly through their own biomass. The mass-specific NH excretion rate by shrimps was similar to aquatic insects, and the areal NH excretion by benthic macroinvertebrates was increased by 2.5 times in the presence of shrimps. In contrast, shrimps excreted significantly less soluble reactive phosphorus (SRP) than aquatic insects, and the presence of shrimps did not affect areal SRP excretion by benthic macroinvertebrates. The field survey showed a positive correlation of NO concentration with the shrimp density, inferring the excess NH was nitrified. Although the nutrient concentration of stream water is frequently attributed to watershed conditions, the results of this study indicate that downstream connectivity to oceans may also influence nutrient dynamics of the stream through the density of amphidromous shrimps.
动物通过摄食和排泄影响生态系统中的元素循环。洄游性虾类经常在中低海拔溪流中占据优势地位，这些溪流与海洋的下游连通性得以维持。尽管已经研究了虾类对底栖群落的直接影响，但它们对养分循环的影响却知之甚少。在这里，我们假设由于虾类和水生昆虫排泄物的质量和数量的差异，虾类的优势会改变底栖大型无脊椎动物在溪流中的养分矿化作用。我们通过野外操纵实验、动物排泄测量和野外调查来验证这一假设。在野外操纵实验中，虾类的存在略微降低了水生昆虫的生物量，但通过自身生物量直接将底栖大型无脊椎动物的总生物量增加了两倍。虾类的比氨排泄率与水生昆虫相似，而在有虾类存在的情况下，底栖大型无脊椎动物的氨排泄面积增加了 2.5 倍。相比之下，虾类排泄的可溶解性反应磷（SRP）明显少于水生昆虫，而虾类的存在并不影响底栖大型无脊椎动物的 SRP 排泄面积。野外调查显示，NO 浓度与虾类密度呈正相关，这表明过量的 NH 被硝化了。尽管溪流水中的养分浓度通常归因于流域条件，但本研究的结果表明，与海洋的下游连通性也可能通过洄游性虾类的密度影响溪流的养分动态。
