Nile Tilapia (Oreochromis niloticus Linnaeus, 1758) Invasion Caused Trophic Structure Disruptions of Fish Communities in the South China River-Pearl River

Simple Summary Biological invasions have become an important part of global change and result in devastating ecological and economic impacts worldwide. Nile tilapia (Oreochromis niloticus Linnaeus, 1758) have been introduced to at least 100 countries for aquaculture, while it is currently recognized as one of the most dangerous invasive species in the tropical and subtropical regions of the world. This study analyzed how Nile tilapia invasion disrupts the trophic structure of native species. The results showed that Nile tilapia invasion reduced the trophic status, shortened the food chain, and affected the isotopic diversity of native fish species. This study provided clear evidence that invasive Nile tilapia could destroy recipient ecosystem stability by disrupting the trophic structure and food chains of native communities. Widespread introductions of non-native species, including aquaculture and ornamental species, threaten biodiversity and ecosystem functioning by modifying the trophic structure of communities. In this study, we quantified the multiple facets of trophic disruption in freshwater communities invaded by Nile tilapia, by comparing uninvaded and invaded rivers downstream of the Pearl River, China. Nile tilapia invasion reduced the trophic status of native fish species by forcing native herbivores and planktivores to seek new food sources. The food chain was also shortened by decreasing the trophic levels of native invertivores, omnivores, and piscivores, while the total isotopic niche area (TA) of native invertivores, omnivores, piscivores, and planktivores species also decreased. Simultaneously, Nile tilapia invasion affected the isotopic diversity of the fish community. Decreasing isotopic richness (IRic), isotopic evenness (IEve), and increasing isotopic uniqueness (IUni) indicated that Nile tilapia had a high trophic niche overlap with native species and competed with native species for food resources, and even caused the compression of the trophic niche of native species. Understanding the process described in this study is essential to conserve the stability of freshwater ecosystems, and improve the control strategy of alien aquatic organisms in south China.