Photogrammetric Analysis of Porites lobata and Pocillopora spp. Live Coral Cover at Devil's Crown, Galapagos Islands, Ecuador

Photogrammetric Analysis of Porites lobata and Pocillopora spp. Live Coral Cover at Devil's Crown, Galapagos Islands, Ecuador

Alvin Sherman Library

Porites lobata and Pocillopora spp. are predominant scleractinian corals at Devil's Crown, Galápagos Islands, Ecuador that have been monitored for 48 years. Fluctuations in colony abundance and live tissue surface area of both taxa are associated with environmental variability driven by El Niño-Southern Oscillation. To better quantify colony number and live tissue cover of the two taxa, photogrammetry was utilized during a research expedition in May 2025. Two GoPro cameras were used during snorkel transects in the northwest (Porites) and northeast (Pocillopora) sectors of the shallow (2-3 m depth), elliptical submerged caldera to produce overlapping digital images. These images were processed in Agisoft Metashape to generate high-resolution photomosaics followed by quantification of planar live tissue cover with TagLab. There were 269 P. lobata colonies within the surveyed area with planar live tissue surface area totaling 65.2 m², representing 19.3% of the total mapped area of 338.4 m². Of these, 235 possessed 100% live tissue cover, while 34 had various amounts of damage. Of the damaged colonies 46.8% was live tissue and 53.2% was dead. Within the area containing Pocillopora spp., all 145 colonies were observed with 100% live tissue surface area, which was 16.0 m², 18.2% of the 88.0 m² area. These spatial metrics provide an improved quantitative assessment of the condition of Porites lobata and Pocillopora spp. at Devil's Crown, enabling future high-resolution comparisons to evaluate temporal changes in coral cover, fragmentation, and recovery following environmental disturbances.