Eighty years of food-web response to interannual variation in discharge recorded in river diatom frustules from an ocean sediment core

Significance Are plants limited by resources or by consumers? Feeding interactions are difficult to observe in nature, so their impacts are commonly underestimated. A record of freshwater diatom frustules in a sediment core collected off the mouth of the Eel River in northern California correlated positively with algal biomass during years when upstream river reaches were surveyed. Our short-term experiments have suggested that year-to-year variation in river algal biomass during the summer growth season was driven by whether or not armored grazers had been scoured away by winter floods. The marine core record also suggests that over 83 years, controls of summer algal production were mediated more by hydrologic impacts on grazers than by their influence on growth conditions for algae.