Close-range underwater photogrammetry for coral reef ecology: a systematic literature review

Close-range underwater photogrammetry, hereafter referred to as photogrammetry, is rapidly emerging as a new standard in measuring and monitoring coral reefs due to its potential to record colony- and habitat-scale metrics in two and three dimensions at sub-centimetre scales. Despite the recent popularisation of photogrammetry, a comprehensive assessment of its applications to coral reefs seascape ecology has not yet been conducted. We systematically reviewed 125 publications on coral reef photogrammetry to assess: 1) its global trends and use; 2) how benthic community data is extracted from imagery; 3) the range of metrics derived and their ecological applications; and 4) key limitations of the approach. Results indicate that development and application of photogrammetry to coral reef ecology has accelerated rapidly in the last 15 years. In total, 55 metrics derived from photogrammetry, grouped in 10 categories, have been used to inform ecological studies on benthic assemblage, habitat structural complexity, and ecosystem condition and trajectory. The high level of effort required to quantify benthic assemblages was identified as a primary workflow bottleneck. We highlight the versatility of photogrammetry to study and monitor coral reef ecosystems and its capacity to quantify benthic community dynamics, habitat, and trajectories, which are vital to inform coral reef conservation and restoration.