Ocean warming exacerbates growth inhibition and alters antioxidant enzyme responses under acute high-level BPA exposure in the commercial red alga Gracilaria lemaneiformis.

Bisphenol A (BPA) is a widely distributed emerging contaminant in coastal waters, yet its interactive effects with ocean warming on commercially important macroalgae Gracilaria lemaneiformis remain poorly understood. To investigate how elevated temperature modulates the physiological responses of the red macroalga G. lemaneiformis to BPA stress, we cultured thalli at two temperatures (20 and 24 ℃) across a gradient of BPA concentrations (0, 1, 2.5, 5, and 10 mg L-1) under controlled laboratory conditions. BPA exerted a strong, concentration-dependent inhibition on growth, photosystem II efficiency, and soluble carbohydrate reserves in thalli. However, low-to-moderate BPA concentrations (1-5 mg L-1) slightly increased photosynthetic pigment content, while high BPA concentration (10 mg L-1) caused a sharp inhibition. Furthermore, warming (24 ℃) exacerbated the negative effects of BPA exposure especially at the highest concentration (10 mg L-1) on G. lemaneiformis but enhanced soluble protein accumulation, indicating respiratory carbon reallocation to support acclimation to thermal stress and BPA exposure. Soluble protein content increased at low-to-moderate BPA levels but declined under high BPA exposure, paralleling the complex regulation of antioxidant enzymes. These findings demonstrate that ocean warming critically exacerbates BPA phytotoxicity in G. lemaneiformis and impairs productivity of this economically valuable seaweed in coastal aquaculture areas facing concurrent pollution and climate warming.