Pressure on the world’s largest living structure keeps mounting. The coral reef, stretching 2,300km along Australia’s north-eastern coast, has suffered two consecutive years of bleaching due to rising sea temperatures. Two-thirds of it is blanched deathly white, having expelled the colourful algae it needs to photosynthesise. Now a plague of reef-munching crown-of-thorns starfish is ravaging its healthier southern end as well. Outbreaks of the venomous invertebrates may be fuelled by nutrients washing into the water, and were responsible for about 40% of lost coral cover before 2012. To prevent even more destruction, scientists are planning a cull in the affected area this month. Mercifully, that area is not already weakened by bleaching, so they hope it will recover. Yet the future looks increasingly bleak. A recent study of 100 reefs showed that bleaching now occurs on average every six years—giving coral little time to regenerate.