What at first appears to be a blanket of fine snow on the sea bed is actually a patch of bleached coral off the northern shore of Papua New Guinea. As sea temperatures rise, this scene is becoming more and more common in coral reefs around the globe. Rising temperatures make corals expel their zooxanthellae (algae with which corals have a symbiotic relationship), leading to starvation.
This is particularly bad news because once a reef dies, it turns to rubble, making it impossible for new coral to grow on top of it. This essentially turns what was once a flourishing biodiversity mini-hotspot into a sort of ecological deadzone.