Coral: structure, reefs, ecology and conservation

Structure and life cycle

A single polyp has a mouth surrounded by tentacles armed with stinging cells. Corals grow by asexual budding to expand a colony and by sexual reproduction — many species release eggs and sperm in synchronized spawning events. The calcium carbonate skeleton produced by stony corals accumulates over generations into the three-dimensional framework known as a reef.

Symbiosis and ecology

Many reef corals live in partnership with photosynthetic algae (commonly called zooxanthellae) that live inside their tissues. These symbionts provide much of the coral's energy through photosynthesis, enabling rapid calcification and vibrant colors. Coral reefs support diverse communities of fishes, invertebrates and plants and provide ecosystem services such as fisheries and coastal protection.

Threats and conservation

• Climate-driven warming and marine heatwaves cause coral bleaching, when symbiotic algae are lost and corals weaken.
• Ocean acidification reduces calcification, while pollution, overfishing and destructive practices degrade reef health.
• Conservation actions include protected areas, restoration projects, improved land-use practices, and research into resilient strains and assisted gene flow.

Corals are both ancient and dynamic components of marine ecosystems. Some species form massive reef structures that take centuries to develop; others are soft-bodied and do not build reefs. Their diversity and vulnerability make corals focal points for science and conservation. For more background on anatomy, taxonomy and current research see overview materials and further resources.