---
source: https://iinventedlight.com/library/notes/coral-reefs-basics.md
title: "Corals and coral reefs: what they are and what threatens them"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NOAA, How does climate change affect coral reefs?, US government work, public domain; NOAA, Corals Tutorial: What are corals?, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: oceans and ecology"
tags: science, ocean, coral, ecology, climate
sources:
  - id: S1
    title: "How does climate change affect coral reefs?"
    publisher: NOAA
    url: https://oceanservice.noaa.gov/facts/coralreef-climate.html
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Corals Tutorial: What are corals?"
    publisher: NOAA
    url: https://oceanservice.noaa.gov/education/tutorial_corals/coral01_intro.html
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Corals and coral reefs: what they are and what threatens them

## Short answer
Corals are animals: colonies of tiny polyps. Hard (stony) corals build reefs from calcium carbonate skeletons, and the reefs support thousands of species and millions of people. Climate change is the greatest global threat to them. [S1][S2]

## Key points
- Most coral polyps feed at night, catching tiny animals with stinging cells called nematocysts. [S2]
- Soft corals do not build reefs, though they live on them. [S2]
- Warmer water brings more mass bleaching and disease outbreaks. [S1]
- The ocean absorbs carbon dioxide, which acidifies it and slows reef building. [S1]

## Claims
- id: C1
  claim: Hard corals produce a rigid calcium carbonate skeleton.
  source: S2
  evidence: "produce a rigid skeleton made of calcium carbonate (CaCO3)"
- id: C2
  claim: Most coral polyps feed at night.
  source: S2
  evidence: "Most coral polyps feed at night."
- id: C3
  claim: Climate change is the greatest global threat to coral reefs.
  source: S1
  evidence: "Climate change is the greatest global threat to coral reef ecosystems."
- id: C4
  claim: Rising temperatures make mass bleaching events more frequent.
  source: S1
  evidence: "mass coral bleaching events and infectious disease outbreaks are becoming more frequent"

## Sources
- [S1] How does climate change affect coral reefs?. NOAA. https://oceanservice.noaa.gov/facts/coralreef-climate.html . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Corals Tutorial: What are corals?. NOAA. https://oceanservice.noaa.gov/education/tutorial_corals/coral01_intro.html . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).