An increasing number of studies describe the ecological influence of semelparous and iteroparous fish migrations on spawning streams. This influence consists of not only the carcasses of spent adults, but also the nutrients that they excrete subsidising stream communities. Given the complex food‐web structure of stream communities, which includes aquatic insects from various functional feeding groups, resource subsidies provided by migratory fishes should influence stream communities through multiple pathways. We evaluated the ecological influence of an iteroparous three‐lips fish (Opsariichthys uncirostris uncirostris) in a alluvial stream by treating fish weirs as large‐scale manipulative field experiments. Between fish‐bearing and fish‐free areas, we compared concentrations of nutrients and fine particulate organic matter (FPOM), and compared densities and stable isotopes of periphyton and benthic macroinvertebrates. The presence of the three‐lips increased the concentrations of ammonium, soluble reactive phosphorus, particulate organic carbon and nitrogen, and chlorophyll‐a densities by up to 2.7‐fold. The δ15N of FPOM and macroinvertebrates during the migratory season were 2.8–7.0‰ higher in the fish‐bearing area, indicating a greater contribution of fish‐derived organic matter. Three‐lips subsidised stream macroinvertebrates through multiple pathways: consumers fed on (1) periphyton increased by the fish nutrient subsidy, (2) fish‐derived organic matter (such as fish carcasses and eggs), and (3) FPOM with fragmented periphyton and fish‐derived organic matter constituents. Results showed that, given the complex food‐web structures in alluvial streams, migratory fish influence stream ecosystems in complex ways. Further studies of the ecological influence of migratory fishes in alluvial streams are needed.
Animals effect 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 massspecific NH4 + excretion rate by shrimps was similar to aquatic insects, and the areal NH4 + 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 NO3 − concentration with the shrimp density, inferring the excess NH4 + was A Self-archived copy in Kyoto University Research Information Repository https://repository.kulib.kyoto-u.ac.jp 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.
Not only through species interactions but also through excretion of nutrients, consumers can have profound effects on the ecosystem structure. While many studies in lentic ecosystems address both effects in combination, little is known about their linkages in lotic ecosystems. By a combination of field manipulative experiment, excretion measurements of consumes, and field surveys, we evaluated biochemical effects of amphidromous shrimps on stream ecosystems. The field manipulative experiment showed that the presence of shrimp suppressed the total aquatic insect biomass by 9% but increased the total benthic macroinvertebrate biomass including the shrimps by 196%. The biomass-specific NH4+ excretion rate by shrimp was similar to aquatic insects, and the calculated mean NH4+ excretion by benthic macroinvertebrate assemblage was 144% higher in the presence of shrimps. On the other hand, shrimps excreted much less PO43− than aquatic insects, and the PO43− excretion by the benthic macroinvertebrate assemblage did not change by the presence of shrimps. The field survey showed a positive correlation between NO3− concentration in stream water and shrimp density, suggesting that the excess NH4+ was nitrified and raised NO3− concentration. In contrast, PO43− concentration in stream water was negatively associated with the shrimp density, indicating that the dominance of shrimps that excrete little PO43− decreased the PO43− concentration. While nutrient concentration of stream water is often attributed to the condition of the watershed area, the results of this study indicate downstream connectivity to the ocean can also influence the nutrient dynamics of the stream through the density of amphidromous shrimps.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.