Most wave protection by an animal structure

The physical structure of coral reefs is largely provided by stony corals - calcium carbonate skeletons made by colonies of animal polyps (order: Scleractinia). These marine structures, which take hundreds of thousands of years to form, attenuate about 97% of incoming wave energy (86% by the reef crest alone), providing protection to some 100 million people around the world who live in coastal zones with offshore reefs. Along with wave energy attenuation by seagrass beds, mangrove swamps and salt marsh vegetation, they are considered nature’s "sea walls".

By area, coral reefs also create the most species-rich habitat on the planet (25% of marine biodiversity in 1% of the ocean). Coral reefs are threatened by climate change (bleaching and ocean acidification), coastal pollution and over-exploitation (over-fishing of species that keep the corals free of overgrowing algae etc, and dynamiting).

The world's longest reef system is the Great Barrier Reef off Queensland, north-eastern Australia, a series of reefs that stretches for some 2,027 km (1,260 mi).