Metrics of Coral Reef Structural Complexity Extracted from 3D Mesh Models and Digital Elevation Models

TLDR

Underwater photogrammetry is increasingly used to generate 3D reconstructions whose extracted habitat metrics can link reef structural complexity to organism distribution. The study aimed to assess how various habitat metrics behave when extracted from Digital Elevation Models and 3D mesh models of simulated bare surfaces and coral morphologies. Simulated 3D models of bare surfaces and coral morphologies were reconstructed, and metrics were extracted from both DEMs and mesh models to evaluate their comparative performance. Results showed that DEM‑derived metrics such as vector ruggedness and fractal dimension consistently ranked structural complexity, with vector ruggedness capturing differences across coral morphologies at multiple resolutions, while profile and planform curvature better captured wall and ledge complexity; overall, DEM metrics are suitable for large overhead plots, whereas vector dispersion is preferable for small, multi‑angle colony plots.

Abstract

Underwater photogrammetry has been increasingly used in coral-reef research in recent years. Habitat metrics extracted from resulting three-dimensional (3D) reconstructions can be used to examine associations between the structural complexity of the reef habitats and the distribution of reef organisms. We created simulated 3D models of bare surface structures and 3D reconstructions of coral morphologies to investigate the behavior of various habitat metrics that were extracted from both Digital Elevation Models (DEMs) and 3D mesh models. Analyzing the resulting values provided us with important insights into how these metrics would compare with one another in the characterization of coral-reef habitats. Surface complexity (i.e., reef rugosity), fractal dimension extracted from DEMs and vector dispersion obtained from 3D mesh models exhibited consistent patterns in the ranking of structural complexity among the simulated bare surfaces and coral morphologies. The vector ruggedness measure obtained from DEMs at three different resolutions of 1, 2, and 4 cm effectively captured differences in the structural complexity among different coral morphologies. Profile curvature and planform curvature, on the other hand, were better suited to capture the structural complexity derived from surface topography such as walls and overhanging ledges. Our results indicate that habitat metrics extracted from DEMs are generally suitable when characterizing a relatively large plot of a coral reef captured from an overhead planar angle, while the 3D metric of vector dispersion is suitable when characterizing a coral colony or a relatively small plot methodically captured from various angles.