Evolution of Coral Rubble Deposits on a Reef Platform as Detected by Remote Sensing

Amelia Shannon,Jody Webster,Ana Vila-Concejo,Hannah Power

doi:10.3390/rs5010001

Abstract

An investigation into the evolution of coral rubble deposits on a coral reef platform is assessed using high-resolution remote sensing data and geospatial analysis. Digital change detection analysis techniques are applied to One Tree Reef in the southern Great Barrier Reef by analysing aerial photographs and satellite images captured between 1964 and 2009. Two main types of rubble deposits were identified: (1) rubble flats that are featureless mass accumulations of coral rubble; and, (2) rubble spits that are shore-normal linear features. While both deposits prograde in a lagoon-ward direction, rubble spits move faster (~2 m/yr) than rubble flats (~0.5 m/yr). The volume of rubble, the underlying substrate, the energy regime, and storm frequency control the rate of progradation. Rubble flat occurrence is restricted to the high-energy (windward) margin of the coral reef platform, while rubble spits are distributed reef wide, both in modal high energy and modal low energy regions of the reef. Rubble spit deposition is considered to be a result of enlarged spur and groove morphology of the forereef, whereby wave energy is focused through the enlarged groove formations causing the preferential deposition of coral rubble in particular zones of the adjacent reef flat. One last control is thought to be the elevation of the reef crest whereby lower areas are more prone to rubble flat development. A vertical and ocean-ward accumulation of rubble is occurring on the windward margin of the reef leading to a build-up and build-out of the reef, governing the expansion of the reef footprint. This study shows for the first time the evolution of a coral reef rubble flat and rubble spits over decadal time scales as detected through remotely sensed images spanning 45 years.

Highlights

Coral reefs are highly complex systems where biological, physical, and chemical processes continually interact over a broad range of spatial and temporal scales [1]
The first is characterised by the southern part of the Eastern Rubble Flat (Sth RF, Figure 1(b)), which corresponds to a featureless evolution with no spits
The second style of evolution is dominated by the formation and progradation of rubble spits, which occurs in the northern part of the eastern rubble flat

Summary

Introduction

Coral reefs are highly complex systems where biological, physical, and chemical processes continually interact over a broad range of spatial and temporal scales [1]. The concept of stability depends largely on the spatio-temporal domain used for analysis, as reefs can appear both as resilient landforms over geological timescales, or fragile systems due to rapid changes over ecological timescales [6]. In this context, the need for an understanding of reef evolution at geomorphological scales is vital as it can bridge the temporal and spatial gap between long-term geological and short-term ecological processes [6,7]. Geomorphological processes within coral reefs usually act over 101–103 m and 101–103 yrs, i.e., the ―planning‖ or

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