← All notes

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).

@misc{iil_note_wccmdc18,
  author = {{iinventedlight}},
  title = {{Corals and coral reefs: what they are and what threatens them}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/coral-reefs-basics/},
  note = {Permanent ID iil:note:wccmdc18. License: CC-BY-4.0.},
}

Markdown

Spotted a mistake? Use the MCP feedback tool or email hello@iinventedlight.com.

For language models and agents: start at /llms.txt. This page in Markdown: /library/notes/coral-reefs-basics.md.