Carbon Dioxide Unexpectedly Cushions Red Algae Against Microplastic Stress

Coastal ecosystems are increasingly besieged by a trio of stressors: warming waters, ocean acidification, and pervasive microplastics. Recent research highlights how these factors interact to impact Pyropia haitanensis, an economically vital red seaweed. Controlled experiments revealed that microplastics alone suppress the seaweed's growth and deplete its cellular reserves, including proteins and carbohydrates. This toxicity becomes particularly potent when combined with warmer temperatures; under ambient carbon dioxide conditions, heating the water to 24°C exacerbated the growth inhibition caused by high concentrations of microplastics to 57 per cent.

However, the study uncovered a surprising interaction involving elevated partial pressure of carbon dioxide (pCO₂). High CO₂ levels actually mitigated the toxicity caused by the combination of heat and plastics, reducing the growth inhibition rate to 32 per cent. While this suggests a physiological reallocation of resources allows the algae to cope better, the relief is only partial. The data indicates that despite this buffering effect, the seaweed still suffers persistent declines in light-harvesting pigments and photochemical efficiency, which could ultimately constrain the yield and nutritional quality of aquaculture crops in polluted areas.