Coral

Corals are marine invertebrate animals, usually colonial, whose polyps secrete calcium-carbonate skeletons. Reef-building corals often host photosynthetic algae that supply much of their energy.

Coral polyp: A small individual coral animal with tentacles surrounding a central mouth. Polyps build coral colonies and secrete the skeleton that supports them.
Cnidaria: An animal phylum containing corals, jellyfish, sea anemones, and hydrozoans, characterized by stinging cells. Corals belong to this phylum and share its distinctive stinging cells.
Coral reef: A marine ecosystem built chiefly from the accumulated skeletons of reef-building corals and other organisms. Coral colonies create the framework that supports reef ecosystems.
Ocean acidification: The decline in ocean pH caused mainly by seawater absorbing carbon dioxide from the atmosphere. Acidification can make it harder for corals to form calcium-carbonate skeletons.
Brain coral: A group of massive corals with winding surface ridges that resemble a brain. Its ridged skeleton shows one of the many growth forms built by coral colonies.
Coral–algal symbiosis: A partnership in which photosynthetic algae live within coral tissue and transfer energy-rich compounds to their hosts. These algae help many reef-building corals meet their energy needs.
Anthozoa: A class of cnidarians that includes corals and sea anemones and has no medusa stage. All corals are anthozoans, though the class also includes non-coral animals.
Coral aquaculture: The cultivation of corals in controlled settings for restoration, research, or the aquarium trade. Cultivated fragments and larvae can supply coral restoration projects.
Marine heatwave: A prolonged period of unusually warm ocean temperatures relative to a region's normal conditions. Heat stress can cause widespread coral bleaching and mortality.
Elkhorn coral: A branching Caribbean reef-building coral with broad antler-like branches. This fast-growing coral contributes complex structure to shallow Caribbean reefs.

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