High impact of low-trophic-position invaders: nonnative grazers alter the quality and quantity of basal food resources

Abstract

AbstractLow-trophic-position animals, such as herbivorous and detritivorous fishes, mollusks, and crustaceans, have been introduced and become established in aquatic ecosystems throughout the globe. After introduction, they have the potential to change community structure and ecosystem processes fundamentally. Armored catfishes (Siluriformes:Loricariidae) are grazing fishes that have an extensive nonnative distribution. High population densities of nonnative loricariids have been linked to the decline of freshwater fisheries in invaded habitats, but the mechanisms underlying declines are poorly understood. We coupled the results of 2 loricariid exclosure experiments with a comparison of invaded and uninvaded sites to measure the effects of loricariids on the quantity and quality of food resources in a tropical stream. Loricariid grazing reduced the standing stock of benthic organic matter and algal biomass in experimental manipulations and in the site comparison. Moreover, grazing by loricariids significa...