Digital Reef Rugosity Estimates Coral Reef Habitat Complexity

Abstract

Ecological habitats with greater structural complexity contain more species due to increased niche diversity. This is especially apparent on coral reefs where individual coral colonies aggregate to give a reef its morphology, species zonation, and three dimensionality. Structural complexity is classically measured with a reef rugosity index, which is the ratio of a straight line transect to the distance a flexible chain of equal length travels when draped over the reef substrate; yet, other techniques from visual categories to remote sensing have been used to characterize structural complexity at scales from microhabitats to reefscapes. Reef-scale methods either lack quantitative precision or are too time consuming to be routinely practical, while remotely sensed indices are mismatched to the finer scale morphology of coral colonies and reef habitats. In this communication a new digital technique, Digital Reef Rugosity (DRR) is described which utilizes a self-contained water level gauge enabling a diver to quickly and accurately characterize rugosity with non-invasive millimeter scale measurements of coral reef surface height at decimeter intervals along meter scale transects. The precise measurements require very little post-processing and are easily imported into a spreadsheet for statistical analyses and modeling. To assess its applicability we investigated the relationship between DRR and fish community structure at four coral reef sites on Menjangan Island off the northwest corner of Bali, Indonesia and one on mainland Bali to the west of Menjangan Island; our findings show a positive relationship between DRR and fish diversity. Since structural complexity drives key ecological processes on coral reefs, we consider that DRR may become a useful quantitative community-level descriptor to characterize reef complexity.

Utilizing Underwater Three-Dimensional Modeling to Enhance Ecological and Biological Studies of Coral Reefs

“…The field of coral reef ecology has recognized complexity to be a critical component of ecosystem diversity and productivity (Goreau 1959, Knudby and LeDrew 2007, Walker et al 2009, Dustan et al 2013), yet there are few methods capable of quantifying intricate 3D features of underwater environments.…”

Reef flattening effects on total richness and species responses in the Caribbean

“…Harborne, Mumby & Ferrari ). Maximum octocoral height (‘ octocoral max height ’) has been used to describe octocoral communities (Lasker & Coffroth ) and was recorded in each plot because soft corals may contribute to structural complexity (Dustan, Doherty & Pardede ). Maximum sponge height in the plot (‘ sponge max height ’) was included because sponges can also act as ecosystem engineers and provide biogenic structures in otherwise low relief habitats (e.g.…”

Measuring coral reef terrain roughness using ‘Structure-from-Motion’ close-range photogrammetry

“…It is easy to calculate and accounts for both horizontal and vertical scales of roughness (Bertuzzi et al, 1990). It is also commonly referred to as "rugosity" within the coral reef literature (e.g., Brock et al, 2004;Knudby and LeDrew, 2007;Friedman et al, 2012;Harborne et al, 2012;Dustan et al, 2013) and has values equal to or greater than one (flat, smooth area), with a typical value of four corresponding to rougher surfaces. The last parameter calculated to characterise surface roughness was the scale-invariant fractal dimension (D).…”

“…Coral reef roughness has been traditionally measured using the chain-method for ecological applications (McCormick, 1994). This technique measures rugosity at a fixed resolution (chain-link size) and is a labour-intensive and time-consuming task (see Dustan et al, 2013 for an improvement on the method). This opposes Hobson's (1972) view of a useful measurement of surface roughness which was characterised as easily measured and comparable across different scales.…”