Wide field-of-view daytime fluorescence imaging of coral reefs

Coral reefs globally are experiencing rapid rates of decline associated with both local and global stressors. Improved monitoring tools are urgently needed to understand the changes that are occurring at appropriate temporal and spatial scales. Coral fluorescence imaging tools have the potential to improve both ecological and physiological assessments. Although fluorescence imaging is regularly used for laboratory studies of corals, it has not yet been used for large-scale in situ assessments. One of the obstacles to effective fluorescence surveying is the need for nighttime deployment, as reflectance from ambient light veils the fluorescence signal. In this paper we describe a method for effective daytime fluorescence imaging with an off-the-shelf camera. The method is based on subtracting an additional image of the ambient light from the daytime fluorescence image. This system enables wide field-of-view fluorophore surveying during the day, opening the possibility for extensive fluorescence surveys with consumer cameras. We also demonstrate the possibility of using a shroud to filter out sunlight in calm water.