Which sea separates Papua New Guinea from Australia?

The Coral Sea, and it holds the Great Barrier Reef along its western edge - 2,300 kilometres of it, the largest structure built by living organisms and visible from orbit.

It was also the site of a battle that changed naval warfare. In May 1942 an American and a Japanese fleet fought for several days without ever seeing each other; every attack was made by carrier aircraft against ships over the horizon. It was the first naval battle in history in which the opposing ships never came within sight, and it ended the era in which fleets closed and fired at each other.

The reef's condition is now the region's defining fact. Mass bleaching events - 1998, 2002, 2016, 2017, 2020, 2022, 2024 - have arrived faster than the ten or so years a damaged reef needs to rebuild. Australia has spent heavily on water quality and crown-of-thorns starfish control and has lobbied hard against UNESCO listing the reef as in danger, which is a diplomatic argument about a scientific question.