Australia | Falling ocean oxygen levels may play a role in reef death at Great Barrier Reef

In March, Australia’s Great Barrier Reef suffered its most widespread bleaching event to date. Sixty percent of the reef underwent moderate to severe bleaching, and some corals may never recover.

The cause of this bleaching event was climate change, which brought unusually warm waters to the Great Barrier Reef in February, and disrupted the delicate, symbiotic relationship between the corals and their life-sustaining algae. In general, when sea temperatures rise, corals become stressed and expel algae from their tissues. Without this algae, the corals turn ghostly white and slowly starve.

https://news.mongabay.com/2020/04/ocean-deoxygenation-could-be-silently-killing-coral-reefs-scientists-say/