Linking Coral Reef Remote Sensing and Field Ecology: It’s a Matter of Scale

Announcing recent publication in the Journal of Marine Science and Engineering (JMSE). The full text is available open-access online: Lucas and Goodman, JMSE, 2015, vol. 3(1): 1-20.

Authors: Matthew Q. Lucas and James Goodman

Abstract: Remote sensing shows potential for assessing biodiversity of coral reefs. Important steps in achieving this objective are better understanding the spectral variability of various reef components and correlating these spectral characteristics with field-based ecological assessments. Here we analyze >9400 coral reef field spectra from southwestern Puerto Rico to evaluate how spectral variability and, more specifically, spectral similarity between species influences estimates of biodiversity. Traditional field methods for estimating reef biodiversity using photoquadrats are also included to add ecological context to the spectral analysis. Results show that while many species can be distinguished using in situ field spectra, the addition of the overlying water column significantly reduces the ability to differentiate species, and even groups of species. This indicates that the ability to evaluate biodiversity with remote sensing decreases with increasing water depth. Due to the inherent spectral similarity amongst many species, including taxonomically dissimilar species, remote sensing underestimates biodiversity and represents the lower limit of actual species diversity. The overall implication is that coral reef ecologists using remote sensing need to consider the spatial and spectral context of the imagery, and remote sensing scientists analyzing biodiversity need to define confidence limits as a function of both water depth and the scale of information derived, e.g., species, groups of species, or community level.

Keywords: coral reefs; remote sensing; field spectra; scale; ecology; biodiversity; conservation coral reefs; remote sensing; field spectra; scale; ecology; biodiversity; conservation

Figure 8. Estimates of biodiversity

Figure 8. Estimates of biodiversity calculated using the exponential of Shannon entropy, exp(H′), illustrating influence of increasing spectral similarity amongst reef species as a function of increasing water depth: 0* is biodiversity obtained from photoquadrats, 0** is biodiversity calculated using only those species considered prevalent or sizable enough to significantly influence the remote sensing signal (i.e., species included in the spectral measurements for this study area), and 0–10 is biodiversity calculated with consideration for optical similarities amongst species (i.e., based on hierarchical clustering of reflectance spectra as influenced by the overlying water column).

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