Comparing Coral Colony Surveys From In-Water Observations and Structure-From-Motion Imagery Shows Low Methodological Bias

As the threats to coral reefs mount, scientists and managers are looking for innovative ways increase scope, scale, efficiency of reef monitoring. Monitoring changes in communities demographic features provides key information about ecosystem function resilience reefs. While most monitoring programs continue rely on in-water visual survey methods, exploring 3D imaging technologies such as photogrammetry, also known Structure-from-Motion (SfM), enhance precision monitoring, logistical field, generate a permanent record reef. Here, we quantitatively compare data generated from surveys SfM-derived metrics assessing demography, bleaching, diversity main Hawaiian Islands part NOAA’s National Coral Reef Program. Our objectives were between-method error within-method error, test bias between identify strengths weaknesses both methods. Colony density, average colony diameter, partial mortality, prevalence species richness, recorded using methods within same areas. For all metrics, magnitude was comparable method significantly higher than SfM one seven metrics. results reveal that majority do not vary nor did observe significant interaction habitat type or depth. Exceptions include estimates bleaching prevalence, Porites juvenile density–though differences generally small. study highlights offers unique opportunity more rigorously quantify mitigate inter-observer by providing observers unlimited “bottom time” work together resolve difficult annotations. However, necessary investment equipment expertise does present substantial up-front costs, time associated with curating imagery, photogrammetric modeling, manual image annotation can reduce timeliness reporting. powerful tool reimagine how manage reefs, this first quantified methodological comparison validate transition standard colony-level surveys.