Onchorynchus mykiss alter nutrient dynamics in high-altitude headwater streams in Boyacá, Colombia through displacement of the native fish community

Abstract

A primary global threat to aquatic ecosystem conservation and biodiversity is the introduction of fish species, both deliberate and unintentional. Much of the research conducted on large predatory fish introductions has focused primarily on top-down controls that regulate the abundance and composition of native species assemblages, yet exotic species that alter ecosystem structure and function may pose an even greater threat. The objective of this study was to examine whether an introduced piscivorous fish alters nitrogen cycles in high elevation freshwater streams in the tropics by displacing the native species community through predation. To test this, we measured biomass and ammonium (NH4+-N) remineralization rates for introduced Onchorynchus mykiss and the two native species found in the area; Trichomycterus bogotensis and Grundulus bogotensis in six study sites along an elevation gradient in the Pómeca River Basin in Boyacá, Colombia. Nonnative O. mykiss populations remineralized ammonium at a rate that was 20 times higher than native G. bogotensis and 47 times higher than T. bogotensis. Our results indicate that high biomass of an introduced predatory fish species can have important implications in nutrient dynamics in freshwater streams through reduction in native species biomass when combined with differential nutrient remineralization rates.