1-hydroxyethane-1,1-diphosphonic acid (HEDP) is accumulated in coastal waters because of its massive industrial consumption, continuous emission and high resistance Gracilariopsis lemaneiformis, a red alga extensively cultured nearshore, is the world's principal biological source of agar and therefore holds substantial economic value. In addition to this commercial role, the alga possesses a remarkable ability to absorb nutrients, making it a promising candidate for bioremediation. This study aims to explore whether large-scale cultivation of G. lemaneiformis can be leveraged to remove HEDP from seawater while concomitantly boosting agar yield. Results show G. lemaneiformis can accumulate agar while metabolizing HEDP. At low concentrations (3.75 mg L-1), HEDP boosts agar content by 25.19 %, reaching 15.84 %, accompanied by upregulated photosynthetic pigment contents, lower starch levels and higher ascorbic acid. The analysis of transcriptome results revealed that the expression of enzymes related to the carrageenan synthesis pathway was significantly upregulated, especially phosphoglucomutase (PGM). However, in comparison to the control (8.72 g), high HEDP concentrations (30 mg L-1) inhibited G. lemaneiformis growth, reducing biomass by 10.37 % (to 7.82 g) on day13. Meanwhile, the rETR was significantly decreased. Importantly, G. lemaneiformis effectively absorbs nutrients and HEDP from the surrounding seawater. Overall, this work establishes an integrated strategy for simultaneously producing premium-quality G. lemaneiformis and efficiently removing HEDP. By integrating seaweed farming with environmental remediation, the approach advances both ecological sustainability and economic profitability.