Quantifying Coral Reef Flat Vertical Accretion Rate Using Photogrammetry

Abstract Monitoring reef growth is essential for understanding sea-level rise impacts on reef-lined coasts. However, measuring coral reef vertical accretion in the field is challenging and rarely achieved. Here we present a method for measuring reef flat vertical accretion at sub-mm scale using close-range structure-from-motion photogrammetry. Comparison of repeat digital surface models constructed from field-based and lab-based photos reveal that the accuracy and precision of the method is on average 0.42 mm and 0.181 mm, respectively. We provide an example of how this method can be utilized to measure reef vertical accretion on a reef flat in the Kingdom of Tonga, South Pacific region. Results reveal the reef accreted by 8.42 ± 0.601 mm over the one-year study period. We highlight the need for future research to scale up the methodology spatially and extend the timeframe of analysis in order to track reef response to ongoing sea-level rise.