River reach types as large-scale biodiversity proxies for management: The case of the Greater Mekong Region

Large-scale development projects such as hydropower dams in the Greater Mekong Region (GMR) exert high pressure on freshwater resources. Environmental impact assessments in the region can help to understand the possible impacts of these projects, yet these assessments typically require biodiversity data that can be both costly and time-intensive to acquire. As a substitute, researchers often assume that river or ecosystem classes based on geophysical characteristics can be used as biodiversity proxies in large-scale assessments to account for a lack of biodiversity data. However, only limited research exists that compares the spatial distribution of river classes and fish species, and therefore it remains unclear how well river classes can represent fish assemblages or, more generally, biodiversity. To address this question, we here compared a new river reach classification, which used regional expert knowledge to build the classes, with a dataset of fish species distribution in the GMR. We conducted a Redundancy Analysis to estimate how much variability in the fish species data can be explained by the river reach types. The results show a moderate correlation between the datasets (adjusted R2 of 0.44). Based on these findings, we elaborate on the role of spatial hierarchy in fish species distribution and discuss possible implications for management and policies in the GMR.