Horseshoe Bay far west

Like all coastlines, Horseshoe Bay has telltale signs of its history of sea level change.

When the last Ice Age was at its deepest, about 20 000 years ago, sea levels were more than 100 m below present levels. At this time the Great Barrier Reef would have existed as a broken line of low limestone hills, covered in vegetation, overlooking the coast, which would have been at the edge of the continental shelf. The sea level rose again after the Ice Age, it fluctuated about 1-2 m above current levels (about 6000 years ago) before settling back to the present level.

Horseshoe Bay's coastal dune features have developed since that time and are a record of those fluctuations and the extremes of cyclones and coast-building climatic events. The high inland dune, 6-8 m above sea level, built up by a combination of wave and wind action, blocks most of the creeks and gullies draining the bay and encloses the Horseshoe Bay Lagoon. At the western end, Gorge Creek and the larger Endeavour Creek, which have cut and maintained an opening through this dune, bank up behind the dune during the wet season until the waters finally break through and deliver a load of granitic sand from the Island hinterland into the bay.

This sand, and a small amount of coral sand from the eroding reef flat, is constantly reworked and distributed along the beach by wave action, slowly building the shoreline outwards. Occasionally, cyclones catastrophically alter the distribution of dunal sand and beaches, but the sand is basically trapped in Horseshoe Bay and, as the shoreline slowly advances, minor dunes are left as relics of previous shorelines.

These coastal processes have developed a comprehensive dune/swale formation with open woodland of Moreton Bay ash (Corymbia tessellaris) and bloodwoods (Corymbia clarksoniana) on the older higher dunes, blue gum (Eucalyptus tereticornis) woodland-favoured lowland food of the koala (Phascolarctos cinereus)-on the lower swale country, and weeping paperbark (Melaleuca leucadendra) forests in the base of the swales.

A riparian closed forest follows the banks of Endeavour Creek with the occasional weeping paperbark and Moreton Bay ash as an emergent and dense vine thicket species underneath.

Apart from the lagoon wetland in the east of the bay, another wetland associated with the vegetation along Endeavour Creek contains a diverse mosaic of plant communities. It contains extensive areas of saltwater wetland (Sporobolis spp. and Paspalum spp.) grassland and smaller areas of freshwater and brackish habitat (Paspalum spp. and Brachiara spp.) grassland. This wetland provides important seasonal habitat and food for wildlife and is of high conservation value.

The unique vegetation of the older, higher dunes reflects the soil and water conditions that have resulted from the changing landforms.