Assessment of hydrogen peroxide as a bioindicator of stress in seaweed aquaculture

The rapid expansion in commercial seaweed farming has highlighted the need for more effective monitoring methods, and health diagnostics. The production of the reactive oxygen species (ROS) hydrogen peroxide (H₂O₂) is a trait that is tied to all major macroalgal groups and holds significance both for its involvement in the oxidative stress response and in the production of climatically relevant gases such as halocarbons. Observations of increased production of H₂O₂ by plants as a stress response, along with its comparative stability and ease of quantification in seawater in comparison to other ROS, suggest that H₂O₂ could be used as an indicator of health. In this study we characterized aqueous H₂O₂ dynamics across a diel cycle, in response to small shifts in light and temperature, as well as when exposed to acute stress. Our results reveal that exposure to acute stressors leads to rapid and sustained concentrations of H₂O₂ that are orders of magnitude higher than changes in H₂O₂ concentrations observed throughout the day. These findings provide tantalizing evidence that monitoring H₂O₂ could be used as a health indicator in seaweed aquaculture and serve as an early warning sign of stress.