Australia’s Great Barrier Reef suffered the worst coral bleaching on record. Both the northern and southern branches of the reef have been battered lately by tropical storms and the encroachment of invasive coral-eating crown-of-thorns starfish, but heat stress driven by warming oceans is the primary cause, scientists told the BBC.
Coral reefs are the most diverse ecosystems in the ocean, holding an estimated 25% of all marine species. They become stressed at high temperatures and expel the symbiotic algae which give coral its iridescent colors: Bleached coral can recover, but if temperatures remain high for long periods or if it faces too many bleaching events in quick succession, it will die.