Lihou Reef

Lihou Reef

Lihou Reef (often referred to as Lihou Reef & Cays) is a large, horseshoe-shaped atoll located in the Coral Sea 575 km southeast from the Queensland city of Cairns — far beyond the boundaries of the Great Barrier Reef. It lies in an isolated and remote oceanic environment at the eastern edge of the Coral Sea Shelf.

Most of the reef system — the largest in the Coral Sea at 2,500 km² in area — is submerged, although there are 18 small sand cays scattered around its perimeter, located on the numerous small segments of the reef rim that are emergent. The low-lying cays have a combined area of around 0.91 km² and range in size from 0.7 ha to 0.17 km². They are composed mostly from exposed coral sand, rock and coral rubble — five of them are vegetated with grasses and shrubs. The vegetated cays are Turtle Islet, Lorna Cay, and along the southern arm of the reef Georgina Cay, Nellie Cay and Anne Cay. The lagoon itself is roughly 100 km long and 30 km wide with maximum depths of up to 60 m.

The unvegetated cays on the reef rim include: Juliette Cay, Kathy Cay, Little Margaret Cay, Margaret Cay, Middle Cay, Observatory Cay, Licklick Cay, Betty Cay, Carol Cay, Dianna Cay, Fanny Cay and Helen Cay. Two of the cays of Lihou Reef have scientific installations installed: there is an automatic weather station on Turtle Islet (at the north-western end of the lagoon) and off the eastern tip of the reef a solar-powered navigation beacon has been set up.

The southwestern end of Lihou Reef, although open to the sea, is in fact marked by a deeply submerged rim, or sill, that is not visible in most satellite imagery. Landsat 7 imagery of this region shows the southwestern rim prominently, revealing the classical ring-like strcture of the atoll. Immediatelty opposite the southwestern rim, 23 km to the west, are the reefs and cays of the Diamond Islets and the Tregosse Reefs.

Being so remote and away from the effects of coastal run-off, the waters in and around the reef can be exceptionally clear — with visibility often down to 60 m. With spectacular underwater scenery, fragile sand cays, prolific seabird populations, and Green Turtle nesting sites, Lihou Reef (along with the Herald Cays and Coringa Islets 100 km to the northeast) were designated as strict nature reserves in 1982. The Lihou Reef National Nature Reserve covers 8,440 km².

image: earth sciences and image analysis laboratory, nasa johnson space center