Masthead Island

Masthead Island Queensland
IUCN category II (national park)
Masthead Island shoreline
Masthead Island
Nearest town or city	Gladstone
Coordinates	23°32′20″S 151°43′36″E / 23.53889°S 151.72667°E / -23.53889; 151.72667Coordinates: 23°32′20″S 151°43′36″E / 23.53889°S 151.72667°E / -23.53889; 151.72667
Area	50 ha (124 acres)
Managing authorities	Queensland Parks and Wildlife Service
Website	Masthead Island
See also	Protected areas of Queensland

Masthead Island is a coral cay located in the southern Great Barrier Reef, 60 kilometres northeast of Gladstone, Queensland. The island is a protected area and forms part of Capricornia Cays National Park. Masthead Island is one of the most undisturbed cays in the national park because human and feral animal impacts have been rare. The cay covers an area of 0.45 square kilometres (0.17 sq mi) and is surrounded by a coral reef that is partially exposed at low-tide. It is part of the Capricornia Cays Important Bird Area.

The island is closed to the public from mid-October to Easter to protect nesting seabirds and turtle hatchlings. At other times the island is open for camping, however there are no facilities provided.

Masthead Island was the shooting location for the 2010 film Uninhabited.

Beach rock is well developed along the southern beach and an occurrence of older beach rock is situated some distance from the beach on the north western corner of the cay. Vegetation is similar to that occurring on Heron island.

The vegetation and tree heights and trunk diameters can be used to interpret coral cay dynamics and thus the growth of the cay. It is postulated that the 'nucleus' old growth Pisonia grandis forest pattern (with trees up to 23m high and 2.4m trunk diameter) is in the central western part of this cay and is able to provide identification of the older forested sections of the island.

The Capricorn and Bunker Cays form part of a distinct geomorphic province at the southern end of the Great Barrier Reef. The cays and their reefs lie on the western marginal shelf, and are separated from the mainland by the Curtis Channel. The cays are not generally visible from the mainland, although Masthead Island may be viewed from Mount Larcom on a clear day.

Geologically the cays are young, having developed during the Holocene period, they are mostly around 5000 years old. The sea level was much lower during the last Ice Age (at the end of the Pleistocene period) and the coastal plain on which today’s reefs and cays developed was completely exposed. Early in the Holocene (around 10,000 years ago) the sea level began to rise, until it stabilised at its present level around 6000 years ago. Once the sea level stabilised, it was possible for reef flats to expand and provide potential sites for the formation of cays.