At a Glance
Four facts to hold on to.
Where
Mostly in tropical waters, about 30°N to 30°S.
Top three
Australia, Indonesia, Philippines: over one-third.
Phyla
About 32 of 34 animal phyla live on reefs.
Hotspot
The Coral Triangle.
In this lesson
Three Confirmed Facts About Coral Reefs
Mostly tropical, and the three-country share
- Most of the world’s coral reefs occur in tropical waters.
- More than one-third lie in the territories of Australia, Indonesia and the Philippines.
- One estimate gives Indonesia about 18%, Australia about 17% and the Philippines about 9% of global reef area.
- Sources: Southeast Asian coral reefs.
More phyla than rainforests
- A phylum is a major group of animals with a shared body plan.
- Coral reefs host more animal phyla than tropical rainforests. This marks their biodiversity value.
- In UPSC’s official key for 2018, all three statements are correct. The answer is option (d).
True or False: Coral reefs host more animal phyla than tropical rainforests.
Where Coral Reefs Concentrate
The Coral Triangle and the Great Barrier Reef
- Indonesia, Malaysia, Papua New Guinea, the Philippines, Solomon Islands and Timor-Leste form the Coral Triangle, a global biodiversity hotspot.
- Australia hosts the world’s largest coral reef system, the Great Barrier Reef.
- Source: Coral Triangle.
A latitude band
- Reefs thrive roughly between 30°N and 30°S.
- They need warm, clear, shallow water.
- The Coral Triangle sits within this band.
True or False: Coral reefs thrive roughly between 30 degrees North and 30 degrees South latitude.
Previous Year Questions
UPSC 2018 tested three statements about coral reefs.
- UPSC 2018The statements were: most reefs occur in tropical waters; over one-third lie in Australia, Indonesia and the Philippines; reefs host more animal phyla than rainforests. UPSC’s official key marks all three as correct. The answer is option (d). View the question.
- UPSC Mains 2019Impact of Global Warming on the Coral Life System.
True or False: UPSC 2018’s official key accepted the claim that over one-third of the world’s coral reefs lie in Australia, Indonesia and the Philippines.
Why Reefs Host So Many Body Plans
The phylum count and structural complexity
- Of roughly 34 recognised animal phyla, about 32 have members on coral reefs.
- Free-living tropical rainforests host only about 9. Counting freshwater and parasitic forms, rainforests reach about 17.
- A reef’s three-dimensional structure creates countless microhabitats.
- These support many distinct body plans, such as sponges, cnidarians, molluscs and echinoderms.
- Source: Reaka-Kudla, reefs compared with rainforests.
Reefs under threat
- Ocean warming and acidification are causing widespread coral bleaching.
- This threatens reef biodiversity globally.
- For India’s reef zones, see the Indian coral reefs lesson.
Think it through: why can a reef host more animal phyla than a rainforest, even though rainforests are often said to hold more species?
Species count and phylum count measure different things. A rainforest holds huge numbers of species, but most belong to a narrower set of body plans, mainly insects and vertebrates. A reef’s many nooks and crevices support sponges, cnidarians, molluscs, echinoderms and dozens more side by side.
True or False: Of roughly 34 recognised animal phyla, about 32 have members living on coral reefs.
True or False: Tropical rainforests host more animal phyla than coral reefs, even though reefs have more total species.
True or False: Ocean warming and acidification are causing widespread coral bleaching, threatening reef biodiversity globally.
Quick Q&A
Where do most reefs lie?
Tropical waters.
Which three countries hold over a third?
Australia, Indonesia, Philippines.
How many animal phyla on reefs?
About 32 of 34.
Largest reef system?
The Great Barrier Reef.
Latitude band?
About 30°N to 30°S.
🎲 Practice: Coral Reefs: Tropical Waters and Animal Phyla
5 verified questions from this topic.
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