Assessing reef island response to environmental conditions on the GBR

Reef island cays form through the deposition of sediment as a result of wave trains converging across

reef platforms and, at the regional scale, are influenced by a range of oceanographic and physical environmental

factors. Preliminary results of a spatial modeling exercise applied to 103 reef islands are presented,

demonstrating that variation in island area and volume can be accurately expressed as a function of latitudinal

and cross-shelf gradients in regional oceanographic factors (exposure to incident waves, tidal range and the

frequency of tropical cyclones) and local physical factors (position on the shelf, area of supporting reef platform,

area of vegetative cover). This morphometric autoregressive model reveals important differences in the

response of unvegetated cays, vegetated cays and low wooded islands to their local environmental conditions.

The empirical relationships defined could further be used to simulate future island accretionary and erosional

dynamics, and consequent vulnerability given information on anticipated environmental changes.