Multiscale structural complexity assessment of coral reefs using underwater photogrammetry

Area of Science:

• Marine biology
• Geoscience
• Digital photogrammetry

Background:

• Coral reef structural complexity is vital for assessing reef health, biodiversity, and resilience.
• Traditional rugosity index methods, like the chain method, fail to capture the full structural intricacies of coral reefs.
• Digital underwater photogrammetry (UWP) enables detailed 3D modeling of reef structures.

Purpose of the Study:

• To introduce and validate a novel wavelet-based method for multiscale analysis of coral reef structural complexity.
• To differentiate between surface (local) and underlying (historical) reef characteristics contributing to complexity.
• To compare the effectiveness of the new method against traditional approaches.

Main Methods:

• Collected UWP data from six reefs in Cozumel Reefs National Park (6–14 m depth).
• Constructed high-resolution Digital Elevation Models (DEMs) and orthomosaics.
• Applied Maximum Overlap Discrete Wavelet Transform (MODWT) to DEM elevation profiles for multiscale decomposition.

Main Results:

• The wavelet-based method successfully decomposed reef topography into local and underlying complexity components.
• Reconstructed DEMs were statistically equivalent to original data (p > 0.05), validating the method.
• Underlying reef characteristics were the primary contributors to complexity estimates.
• Significant differences in structural complexity were found between reefs (p < 0.05).
• Agariciid and branching corals were key drivers of surface complexity in the study area.

Conclusions:

• The wavelet-based method provides a more thorough assessment of reef structural complexity than the chain method.
• Traditional methods may undervalue the historical context and local characteristics crucial for reef resilience.
• Understanding multiscale complexity is essential for effective coral reef management and conservation.