Comparison of shadow rugosity versus chain-tape rugosity values from 3D coral reef models

Abstract

Structural complexity of coral reefs has been shown to be correlated with important ecological parameters such as fish abundance and diversity, and reef health. It is usually measured through getting a one dimensional index called linear rugosity or an area based metric surface rugosity from 3D models created with structure-from-motion. In this paper, shadow rugosity, which is a faster alternative that makes use of shadow cues from reef features and has previously shown positive correlation with linear rugosity obtained from simulated reefs, is applied on 3D coral reef models. We show that shadow rugosity values are positively correlated with surface rugosity and can be used to rapidly derive representative values of structural complexity from existing underwater digital images.