Quantifying The Effects of Colony Size, Morphology, and Bleaching on Growth Rates of the Coral Montipora Capitata Using 3D Structure-From-Motion Photogrammetry
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Lawlor, Colleen Marie
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Marine Science
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Coral growth plays a vital role in forming the structural complexity that supports reef biodiversity, but can vary widely across species and locations, with Hawaiian corals reported to be among the slowest growing. Here we follow 103 individual colonies of the Hawaiian scleractinian coral Montipora capitata over 21 months to quantify growth using 3D models created using Structure-from-Motion (SfM) photogrammetry. Colony size, rugosity, and bleaching occurrence were significant predictors of coral growth rate, which increased colony size by an average of 180% (planar area) to 210% (3D surface area). Both measures of area were significantly correlated (r=0.98), highlighting the utility of either measure, even in a species with highly plastic growth morphology like M. capitata. Total growth was positively correlated with colony size such that larger colonies grew more than smaller ones, but proportional growth was highest (up to ~3% / day) in small colonies. Rugosity was negatively correlated with growth rate, as colonies with plating morphologies grew faster than branching morphologies. The relationship between rugosity and size is complicated, however, because rugosity increased significantly throughout the study with smaller colonies showing the greatest increase in rugosity through time. Corals that experienced bleaching during the 2019 heat wave (35 of 103) showed significantly lower growth (1.67 fold) than colonies that did not bleach, despite 100% recovery of bleached colonies. This study highlights some of the complexity in estimating and comparing coral growth rates and documents a long-term impact of non-lethal bleaching on subsequent coral growth rate.
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Hawaii Pacific University