Fish Abundance and Functional Composition Are Associated With Water Type and Climate Across Amazonian Wetlands

Abstract

Aim

We evaluate how Amazonian water types and broad-scale climatic and productivity-related proxies are associated with fish abundance and functional composition across wetlands.

Location

Amazon Basin, South America.

Taxon

Freshwater fishes.

Methods

We analysed fish assemblage data from 85 wetlands distributed across whitewater, blackwater and clearwater systems. Sampling effort was standardized using gillnet-effort metrics (m²·h) across comparable sampling protocols, and abundance was expressed as catch per unit effort (CPUE). We evaluated the relative influence of water type, climatic and productivity-related proxies and spatial structure on fish abundance and functional composition using generalized linear mixed models and multivariate analyses of community-weighted traits.

Results

Fish abundance was higher in whitewater than in blackwater wetlands, with whitewater wetlands supporting approximately 2.1 times higher abundance. Fixed effects explained 23% of the variation in fish abundance. Functional composition also differed among water types, although the effect size was modest (permutational multivariate analysis of variance [PERMANOVA], R² = 0.082). Blackwater wetlands showed higher relative contributions of piscivores and intermediate strategists, whereas clearwater wetlands were associated with periodic-small and piscivores. Whitewater wetlands showed relatively higher contributions of intermediate strategists and piscivores. Overall, differences among water types were more evident for trophic guilds and life-history strategies than for body-size or reproductive traits. Climatic and productivity-related proxies, water type and spatial structure jointly explained 17.8% of the variation in functional composition (adjusted R² = 0.178), with environmental variables accounting for the largest pure fraction of explained variation.

Main Conclusions

Climatic and productivity-related proxies, together with water type and spatial structure, were associated with broad-scale variation in fish assemblage structure. By integrating environmental proxies and functional traits, our study highlights how large-scale environmental heterogeneity is associated with variation in fish abundance and functional strategies across the world's largest tropical wetland system.