Macroalgal ecosystem provides a scalable solution to coastal herbicide pollution via macroalga–microbiome synergy

The increasing discharge of land-derived phytotoxic herbicides threatens oceanic primary production by inhibiting phytoplankton photosynthesis. Macroalgae also contribute significantly to ocean productivity, yet their responses to herbicides remain poorly understood. Here, using the annual Ulva prolifera green tide in the Yellow Sea as a natural model, we show that large-scale macroalgal blooms act as an effective multi-pathway bioremediation system for herbicides. U. prolifera reduced triazine herbicide concentrations by 32–89% across coastal waters, with some compounds becoming undetectable. The macroalgae displayed strong tolerance to atrazine and achieved high removal efficiency through direct bioaccumulation (bioconcentration factor >5,000 L/kg) coupled with synergistic interactions with associated bacteria. Moreover, U. prolifera enriched key degrader taxa (Rhodobacteraceae, Methylophagaceae, Methylophylus, Alteromonas), enhancing atrazine degradation 2.5-fold via complementary metabolic pathways including dichlorination and dealkylation. These findings reveal a previously overlooked role of macroalgal ecosystems in sustaining coastal resilience and underscore their potential as scalable, nature-based solutions to mitigate herbicide pollution in global oceans. Ulva macroalgal ecosystem is a highly efficient natural bioremediation system, reducing coastal triazine herbicides by up to 89% through pathways involving macroalga-microbiome synergistic functions, according to a field investigation combined with designed simulation conducted in Yellow Sea, China.