Grassroots reserves rescue a river food web from cascading impacts of overharvest

Abstract

Intensive fishing is altering the functioning of aquatic ecosystems worldwide, threatening both biodiversity and food security. No‐fishing reserves have proven effective at restoring food‐web structure and enhancing fisheries in marine ecosystems, but remain virtually untested in freshwater systems. Using experiments inside and outside of community‐created riverine reserves in Thailand, we describe a trophic cascade across six trophic levels, from humans to algal responses to nutrient availability. Protection from fishing profoundly reconfigures fish communities – greatly increasing biodiversity, biomass, and body size – yet mean trophic position was unaffected. Cascade dynamics from fish to algae were observed regardless of protection status, although fishing intensified trophic interactions through strong effects on grazing insect behavior. The marked effectiveness of these small, grassroots reserves offers an important conservation‐planning model for protecting food webs and augmenting fishery yields in biodiverse tropical rivers.