Lower rainfall linked to simpler river food webs

A four-year study of nine rivers in South Texas found that sites with less annual rainfall had less complex food webs and different distributions of animal biomass. Researchers sampled fish, snails, algae and other organisms along a natural rainfall gradient. ^[1]

The drier-stream sites had twice the secondary production—the growth of new animal tissue over time—and biomass turnover rates of the wetter sites, according to the study report. Researchers also described a shift toward a bottom-heavy biomass pattern, with a greater share of animal mass lower in the food web. ^[1]

The findings show an association across these South Texas rivers, not proof that rainfall alone caused the differences or that the same patterns occur elsewhere. The report says more field data and improved models are needed to understand rainfall’s effects across ecosystems. ^[1]