Trophic linkage of a temperate intertidal macrobenthic food web under opportunistic macroalgal blooms: A stable isotope approach

•Trophic effects of Ulva blooms on intertidal macrobenthic food web were evaluated.•Biomasses of Ulva increased at the macroalgae-bloom from March to September.•δ13C and δ15N values of consumers differed with feeding strategy and season.•Trophic significance of blooming macroalgae varies with feeding strategies of consumers.•Ulva blooms play a significant role as a basal resource supporting the intertidal food web.

The effects of blooms of opportunistic green macroalgae, Ulva prolifera, on the trophic structure of the macrobenthic food web in a temperate intertidal zone on the western coast of Korea were evaluated using carbon and nitrogen stable isotopes. Biomasses of Ulva and microphytobenthos (MPB) increased significantly at the macroalgae-bloom and the non-bloom sites, respectively, from March to September 2011. The δ13C values of most the consumers were arrayed between those of MPB and Ulva at both sites, and differed according to feeding strategies at the macroalgae-bloom site. Seasonally increasing magnitudes in δ13C and δ15N values of consumers were much steeper at the macroalgae-bloom site than at the non-bloom site. Our findings provide evidence that blooming green macroalgae play a significant role as a basal resource supporting the intertidal macrobenthic food web and their significance varies with feeding strategies of consumers as well as the resource availability.