Abstract
We assess 90 years of change on a Low Wooded Island (Low Isles, Great Barrier Reef), employing drones and topographic profiling to accurately survey ramparts, mangroves, the reef flat and the sand cay. A comparison with maps from the 1928–1929 Great Barrier Reef Expedition revealed the redistribution of an outer rampart and inward movement of shingle ridges. Remarkable lateral expansion of the mangrove woodland some 400 m has occurred as carbonate sand deposition has increased reef flat elevation, obscuring coral microatolls. The sand cay has stayed relatively constant in size, moving approximately 44 m in a northeasterly direction and rotating slightly. We conclude that the existing configuration of landforms probably represents an equilibrium with local biophysical conditions, including sea level, wave dynamics, vegetation growth, storms and cyclones. The variable nature of ramparts and the presence of a trough that prevents the continuous spread of mangroves across a uniformly flat colonization surface precludes the interpretation of landform changes with respect to a geomorphic evolutionary sequence. Moreover, longer-term implications of environmental change for these landforms can only be evaluated once the specific nature of the local carbonate budget, including the relative contribution of corals, foraminifera and Halimeda has been elucidated.
Highlights
No coral island in the world has been so intensively studied over so long a time as Low Isles, the southernmost low wooded island of the Great Barrier Reef [1].First described by Cook in 1770, with subsequent descriptions by King in 1819 and MacGillivray in 1848, Low& 2019 The Authors
The main changes observed over the 90-year period of assessment at Low Isles include the redistribution of outer ramparts on the eastern reef flat between transects 4 and 5, suggesting royalsocietypublishing.org/journal/rsos R
(2) The mangrove forest occupying the windward side of the reef flat known as ‘Woody Island’ 17 expanded laterally some 400 m as the reef flat has become elevated through carbonate sand deposition, with notable mangrove colonization around the periphery of the area known as Porites Pond
Summary
No coral island in the world has been so intensively studied over so long a time as Low Isles, the southernmost low wooded island of the Great Barrier Reef [1]. 1. Physiographical sketch map of ‘Low Islands’ made by EC Marchant in 1928 for the purpose of discussing island formation using a plane table during the 1928– 1929 Great Barrier Reef Expedition. 2. Coloured map of Low Isles surveyed by M Spender, Mrs TA Stephenson and EC Marchant in 1929 initially at scale of 1 : 2400 and published in the Geographical Journal in 1930 at scale of 1 : 5000 as fold-out map
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