- marine biome built from calcium carbonate skeletons secreted by coral polyps
- the rainforest of the sea: hosts 25% of all marine species on less than 1% of ocean floor
- symbiosis between coral and zooxanthellae algae drives reef productivity through photosynthesis
- three types: fringing, barrier, and atoll (formed around subsiding volcanoic islands)
- Great Barrier Reef is the largest living structure visible from space
- reef growth requires warm, clear, shallow water with specific climate zone conditions
- threatened by ocean warming (bleaching), acidification (from carbon cycle disruption), and pollution
- provides coastal protection, fisheries, tourism, and pharmaceutical compounds
- evolution of scleractinian corals spans 240 million years
- recovery from bleaching events takes decades if conditions stabilize
- essential for marine ecology and the livelihoods of 500 million people