The Great Barrier Reef runs for several thousand kilometres up the east coast of Queensland and, out from Port Douglas, sits neatly on the edge of the Australian continental shelf. It’s at this point that the continental shelf falls sharply away into Outer Barrier Reef and the Continental Shelfthe Coral Sea, in places forming an underway cliff that can drop up to 1,000 metres.

The ‘outer reef’, as it is known, benefits from