Benthic and terrestrial invertebrates support fish communities of amazonian streams

Abstract

The Amazonian stream network is impressive not only for its vastness but also for harboring a great diversity of fish species. Despite their high diversity, little is known about key ecological aspects of Amazonian streams such as energy flow and the carbon sources that sustain their species-rich fish assemblages. In this study we use carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotopes to evaluate the trophic structure and to identify the key food resources sustaining the ichthyofauna of Amazonian streams. We collected fish assemblages and a wide range of resources available in streams, including macrophytes, riparian vegetation, filamentous algae, organic matter, grasses, benthic and terrestrial invertebrates, periphyton, and suspended matter. We then estimated the trophic structure of the assemblages, including diversity metrics, trophic niches, positions, assimilated resource proportions, and biomass. Fish biomass was primarily supported by terrestrial invertebrates (31%–55%) and benthic invertebrates (22%–40%). Shrimps represented the third most important resource for fish biomass (9%–22%). Together, these three resources accounted for 79%–90% of the total fish biomass in the studied streams. The trophic structure and trophic diversity metrics were similar across all sampling sites, as evidenced by the substantial overlap in the isotopic niche of the assessed fish assemblages. Although trophic positions varied to some extent among sites, most species fed at intermediate trophic levels. Our results highlight the importance of both aquatic and terrestrial invertebrates in supporting fish trophic dynamics in Amazonian streams, reinforcing the interconnections between small streams and their surrounding landscapes. It also underscores the role played by forests in maintaining the integrity of Amazonian aquatic environments by providing food resources that sustain fish assemblages. Therefore, our study provides essential insights into the carbon flow and isotopic ecology in small Amazonian streams, which are vital for understanding their functioning, guiding conservation efforts, and ensuring the sustainable management of natural resources.