Corals

Corals are animals — specifically, they are colonial cnidarians related to jellyfish and sea anemones. Each coral colony is made up of thousands of tiny individual animals called polyps, each typically just a few millimetres in diameter. Polyps secrete calcium carbonate skeletons that accumulate over centuries to form the massive reef structures we see today. Most reef-building corals have a symbiotic relationship with microscopic algae called zooxanthellae that live within their tissues. These algae photosynthesise, providing up to 90% of the coral's energy needs, and give corals their characteristic colours.

Coral reefs are often called the 'rainforests of the sea' for their extraordinary biodiversity. A single reef system can support thousands of species of fish, invertebrates, algae and microorganisms, all interconnected in complex food webs. Reefs provide essential services: they protect coastlines from wave erosion, provide nursery habitat for commercially important fish species, support tourism industries worth billions of dollars annually, and are a source of compounds used in medicines. The Great Barrier Reef alone supports over 1,500 fish species, 4,000 mollusc species and 240 bird species.

Coral bleaching occurs when corals are stressed — most commonly by elevated water temperatures — causing them to expel their zooxanthellae. Without these algae, corals turn white (bleach) and, if the stress persists, die. Mass bleaching events have become more frequent and severe as ocean temperatures rise due to climate change. The Great Barrier Reef experienced unprecedented mass bleaching events in 2016, 2017, 2020, 2022 and 2024. While corals can recover from bleaching if conditions improve quickly, repeated events prevent recovery and lead to permanent reef degradation. Scientists project that at 2°C of global warming, 99% of coral reefs will bleach annually.

Protecting coral reefs requires action at multiple scales. Locally, reducing direct pressures — overfishing, coastal pollution, destructive fishing practices and physical damage — gives reefs the best chance of surviving climate stress. Marine protected areas, when properly enforced, can significantly improve reef resilience. Globally, reducing greenhouse gas emissions is the only way to prevent the ocean warming and acidification that threatens reefs at their foundation. Innovative conservation approaches include coral gardening (growing and transplanting coral fragments), assisted evolution (breeding heat-tolerant corals) and reef restoration. However, these interventions cannot substitute for addressing the root cause of climate change.