Biogeochemical water type influences community composition, species richness, and biomass in megadiverse Amazonian fish assemblages

Abstract

Amazonian waters are classified into three biogeochemical categories by dissolved nutrient content, sediment type, transparency, and acidity—all important predictors of autochthonous and allochthonous primary production (PP): (1) nutrient-poor, low-sediment, high-transparency, humic-stained, acidic blackwaters; (2) nutrient-poor, low-sediment, high-transparency, neutral clearwaters; (3) nutrient-rich, low-transparency, alluvial sediment-laden, neutral whitewaters. The classification, first proposed by Alfred Russel Wallace in 1853, is well supported but its effects on fish are poorly understood. To investigate how Amazonian fish community composition and species richness are influenced by water type, we conducted quantitative year-round sampling of floodplain lake and river-margin habitats at a locality where all three water types co-occur. We sampled 22,398 fish from 310 species. Community composition was influenced more by water type than habitat. Whitewater communities were distinct from those of blackwaters and clearwaters, with community structure correlated strongly to conductivity and turbidity. Mean per-sampling event species richness and biomass were significantly higher in nutrient-rich whitewater floodplain lakes than in oligotrophic blackwater and clearwater river-floodplain systems and light-limited whitewater rivers. Our study provides novel insights into the influences of biogeochemical water type and ecosystem productivity on Earth’s most diverse aquatic vertebrate fauna and highlights the importance of including multiple water types in conservation planning.

The Amazon River microbiome, a story of humic carbon

“…Water type has been shown to be a major driver of the diversity, composition and population genomics of eukaryotic biological communities in Amazonia. This has been shown in a vast array of species including teleosts [44][45][46][47], phyto and zooplankton [48], as well as periphyton communities [49]. There has also been a few studies focused on Amazonian bacterioplankton, although most of them did not sample in different water types [20,[35][36][37][38][50][51][52][53][54].…”

A fossil fish assemblage from the middle Miocene of the Cocinetas Basin, northern Colombia

“…The differences in similarity patterns between the Miocene assemblages and the present-day basins might be due in part to differences in local ecological conditions (e.g., water chemistry; Arbeláez et al . 2008; Bogotá-Gregory et al . 2020) in addition to zoogeographic patterns in space, or faunal turnover in time.…”

Spatial and Long-Term Temporal Changes in Water Quality Dynamics of the Tonle Sap Ecosystem

“…For example, Chea et al [2] showed that spatial patterns of DO, pH, and TP influenced the spatial structure of the fish assemblages in the Lower Mekong River. It is likely that variations in water quality in the TSE drive some of the spatial and temporal variation of fish catch, similarly to what has been found in [78] and in the Amazon River [79]. We recommend spatially distributed water concentration monitoring in the same locations of fisheries monitoring to answer these questions and predict future fish diversity and yield scenarios.…”