Monitoring water quality from space: Benthic light as a new indicator of water quality for corals and seagrasses of the Great Barrier Reef

Reduced light due to poor water quality is a driver of chronic stress for corals, seagrasses, and the habitats that they create. We have developed a new water quality index to monitor the amount of light stress experienced by corals and seagrasses in any part of the GBR over the course of each year. We use satellite ocean colour observations to estimate the amount of light reaching benthic habitats across the whole GBR each day and relate this to the habitat requirements of corals and seagrasses. The new index is sensitive to interannual and regional variations in water quality. After accounting for variations due to acute stress from bleaching and CoTS outbreaks, it explains a greater proportion in change in coral condition over time than previously used river discharge or satellite water quality metrics. Benthic light is also effective as an input to models that predict the distribution and community composition of seagrasses. We therefore conclude that the new index is suitable for use as an ecologically relevant indicator of water quality in the GBR.