Coral: Key Facts & Natural History

Quick answer

Corals are small marine animals in the class Anthozoa, related to sea anemones and jellyfish, that often live in vast colonies of individual polyps. Reef-building corals secrete hard calcium carbonate skeletons that, over thousands of years, form the largest living structures on Earth. Many depend on algae living in their tissue for food and color, and a single colony can live for decades or longer.

By Kaiser Khan , Founder Last reviewed July 10, 2026 How we research & review

Key takeaway

Overview

Biology

Coral (Anthozoa) is classified as Invertebrate with conservation status Least Concern. Typical weight about 1 kg; lifespan around Colonies can live decades to centuries.

Ecology

Diet: Filter feeder plus algae symbionts. Habitat: Warm, shallow tropical seas worldwide. Movement and social systems reflect those pressures.

People and this species

Learn before you travel or keep related pets. Wild individuals are not toys; captive care needs species-specific husbandry.

Tiny animals, giant reefs

Each coral is built from many small animals called polyps, soft cup-shaped bodies ringed with stinging tentacles. Reef-building corals secrete hard skeletons of calcium carbonate beneath them, and as generations stack up over thousands of years they form reefs. The Great Barrier Reef, made by countless coral colonies, is so large it can be seen from space.

A partnership with algae

Many corals host tiny algae called zooxanthellae inside their tissue, which photosynthesize and supply much of the coral's food and its bright color. In return the coral gives the algae shelter and nutrients, a partnership that lets reefs thrive in clear, sunlit, nutrient-poor tropical waters. Corals also catch plankton and tiny animals using their stinging tentacles, especially at night.

Reproduction and growth

Corals can reproduce both by budding, where polyps clone themselves to expand a colony, and by spawning, releasing eggs and sperm into the water. On many reefs, mass spawning events see corals release their eggs and sperm together on the same few nights of the year. Growth is slow, with many corals adding only a few centimeters or less per year.

Bleaching and conservation

When water becomes too warm or polluted, corals expel their algae and turn white, an event called bleaching that can kill them if conditions do not improve. Climate change, ocean acidification, pollution, and destructive fishing all threaten reefs worldwide. Because reefs support a quarter of all marine species, their protection is a major global conservation priority, and the status of individual coral species varies widely.

Research notes

Figures for corals (Anthozoa) come from field studies, museum records, and conservation assessments that do not always agree on exact averages. Prefer ranges over single-point claims, and check whether a source describes wild, captive, or mixed populations.

Practical takeaways

If you encounter corals in the wild, prioritise distance and local guidance. If you care for related domestic or captive animals, match diet and housing to species needs rather than generic pet advice. Share accurate status information (Least Concern) when discussing conservation.

Sources

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