The worst coral bleaching event on record has caused havoc to the world's reef systems, with scientists calling for urgent action against climate change to reverse the damage caused to the underwater ecosystems.

Pictures from the XL Catlin Seaview Survey show the devastating impact of unusually warm water on corals around the Japanese islands of Okinawa. Corals are seen "fluorescing" in bright colours – an indicator that they are stressed and losing their vitality.

"If ever there was a wake-up call to the threat of climate change, this is it," the not-for-profit Ocean Agency says. "We are seeing an entire ecosystem in a rapid state of collapse. It is a dire warning we can't afford to ignore."