For more than a decade it has featured on the world's maps. Viewed from Google Earth, Sandy Island appears as a dark, tantalising sliver, set amid the shimmering vastness of the Pacific Ocean.

But when marine scientists arrived at the island in the Coral Sea off Australia they were in for something of a shock: it didn't exist. Where there was supposed to be a sandy outcrop complete with palm trees, a few coconuts and maybe a turtle there was merely blue undulating water