Trophic response of fishes to rainfall variability in a temperate estuarine system of Korea: A stable isotope approach

To assess the basal resources supporting food webs impacted by rainfalls, we compared stable isotope ratios (δ13C and δ15N) of fish consumers and organic matter sources between up- and down-sites in an estuary between seasons (June and September) and years (2018 and 2019) that showed different patterns of summer monsoon. Our study showed seasonal differences in the δ13C and δ15N values of basal resources and fish consumers in both years. At the up-site, significant differences of δ13C values of fish consumers were found between years, resulting from changing rainfall period, thereby causing a shift in food availability from terrigenous organic matter to periphyton. In contrast, at the down-site, the consistent isotopic values of fishes were observed in both years, suggesting that rainfall shift has a negligible impact on resources for fishes. Overall, the annual shift in resources for fishes in the estuary may be controlled by contrasting rainfall events. •Rainfall effects on the fish trophic structure of an estuarine system were assessed.•Fish δ13C and δ15N examined at up- and down-sites between pre- and post-monsoon.•Spatial and temporal differences in consumer resources were continually observed.•Basal resources for fishes were significantly affected by altered rainfalls.•Our findings highlight estuarine trophic modification impacted by changing rainfalls.