Environmental DNA reveals anthropogenic impacts on fish diversity in mountain streams and the increasing risk of species invasion

Abstract

Fish diversity and population dynamics are critical to freshwater ecosystem health. However, the direct disturbance of fish communities resulting from human activities and indirect impacts during environmental modifications pose significant risks to fish diversity. In this study, we employed eDNA metabarcoding technology to investigate the diversity and distribution of fish in the main water sources of the Zhejiang Jiulongshan National Nature Reserve. A total of 11 orders, 24 families, 47 genera and 61 species of fish, including 5 exotic species, were identified. The results revealed a greater number of fish species at the lower-elevation sampling sites but greater uncertainty at the higher-elevation sampling sites. However, small numbers of exotic fish species were observed at almost all the sampling sites. Cypriniformes served as biomarkers at the sampling sites with tourism activities, whereas more unique taxonomic units, such as Siluriformes and Gobiiformes, were observed at the sampling sites without tourism activities. Many environmental factors were significantly correlated with fish community differences within and outside the core area. Notably, the mean total organic carbon (TOC) and mean chemical oxygen demand (COD) levels were 8.73 % and 17.51 % greater, respectively, in the core area than outside the core area. In contrast, the phosphate, sulfide, Fe and pH levels were greater outside the core area than inside the core area. Our study revealed anthropogenic disturbances to biological communities in freshwater ecosystems by investigating the distribution and abundance of fish OTUs. Changes in the aquatic environment and biological invasions triggered by the activities of indigenous people, ecotourism and the operation of artificial fishponds may be the main risk factors influencing fish diversity in mountain streams.