Associations between Benthic Cover and Habitat Complexity Metrics Obtained from 3D Reconstruction of Coral Reefs at Different Resolutions

Atsuko Fukunaga,Randall K Kosaki,John H R Burns,Kailey H Pascoe

doi:10.3390/rs12061011

Abstract

Quantifying the three-dimensional (3D) habitat structure of coral reefs is an important aspect of coral reef monitoring, as habitat architecture affects the abundance and diversity of reef organisms. Here, we used photogrammetric techniques to generate 3D reconstructions of coral reefs and examined relationships between benthic cover and various habitat metrics obtained at six different resolutions of raster cells, ranging from 1 to 32 cm. For metrics of 3D structural complexity, fractal dimension, which utilizes information on 3D surface areas obtained at different resolutions, and vector ruggedness measure (VRM) obtained at 1-, 2- or 4-cm resolution correlated well with benthic cover, with a relatively large amount of variability in these metrics being explained by the proportions of corals and crustose coralline algae. Curvature measures were, on the other hand, correlated with branching and mounding coral cover when obtained at 1-cm resolution, but the amount of variability explained by benthic cover was generally very low when obtained at all other resolutions. These results show that either fractal dimension or VRM obtained at 1-, 2- or 4-cm resolution, along with curvature obtained at 1-cm resolution, can effectively capture the 3D habitat structure provided by specific benthic organisms.

Highlights

Scleractinian corals are ecosystem engineers that play an important role in coral reef ecosystems by providing a three-dimensional (3D) habitat structure that alters the physical environments and increases the availability of habitat for reef organisms [1]
The present study was built on our previous work that investigated the behavior of different habitat metrics calculated from digital elevation models (DEMs) at 1-cm resolution, which were generated from 3D reconstructions of the same coral reef habitats in the Northwestern Hawaiian Islands (NWHI) [20]
Fractal dimension combines information obtained at various spatial scales (1 to 32 cm in our case), and while applying the concept of fractal dimension to quantifying the surfaces of coral heads or colonies [33,34] or to estimating the structural complexity of coral reefs [17,35] is not new, our results demonstrate that this multiscale metric obtained from DEMs is superior to either surface complexity or slope in terms of capturing the structural complexity of reef organisms

Summary

Introduction

Scleractinian corals are ecosystem engineers that play an important role in coral reef ecosystems by providing a three-dimensional (3D) habitat structure that alters the physical environments and increases the availability of habitat for reef organisms [1]. Coral growth forms affect the distribution of reef fish, with morphologically complex corals (e.g., branching forms) supporting more diverse and abundant fish assemblages [4,5,6]. Quantifying the 3D habitat structure of coral reefs is, important when assessing the status of biological communities of coral reefs, as these data allow researchers to evaluate the effects of structural complexity on associated reef organisms [3]. Bleaching events often result in a loss of morphologically complex corals and overall reef structural complexity [13] These detrimental shifts in coral assemblage structure highlight the importance of continuous monitoring efforts that assess the status of coral reef communities and how changes in reef architecture affect the abundance and diversity of associated organisms

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