Coral Reefs and Marine Ecosystems
Reefs host a quarter of marine species but are threatened by warming and acidification.
About this topic
Coral reefs are built by tiny coral polyps, which live in symbiosis with algae (zooxanthellae) that photosynthesise and give the coral food and colour. Reefs cover less than 1% of the ocean floor but support about 25% of marine species. They protect coasts and support fishing and tourism.
Polyps secrete calcium carbonate skeletons, which build up over centuries into reefs such as the Great Barrier Reef. Reefs need warm, clear, shallow, sunlit water with the right salinity. The ocean as a whole also includes open water plankton, kelp forests, deep sea and estuaries, each with their own food webs based on phytoplankton.
Threats include warming seas, which cause bleaching: stressed coral expels its algae, turns white and may die. Ocean acidification, caused by CO₂ dissolving in seawater, makes it harder to build skeletons. Pollution, runoff, overfishing and destructive practices like blast fishing add to the damage.
Protection includes marine reserves, sustainable fishing, reducing emissions and restoring reefs by growing coral fragments. A common misconception is that coral is a plant or rock; it is an animal. Bleached coral is not yet dead and can recover if conditions improve quickly.
Key ideas
- Corals live with algae in symbiosis
- Bleaching occurs when water is too warm
- Reefs protect coasts
Quick check
Use cases: where Coral Reefs and Marine Ecosystems helps
- Homework: review the key idea behind Coral Reefs and Marine Ecosystems before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Coral Reefs and Marine Ecosystems without notes.
- Visual learning: play with the interactive lab to see how Coral Reefs and Marine Ecosystems changes when you adjust its inputs.
- Teaching a friend: explain Coral Reefs and Marine Ecosystems in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Coral Reefs and Marine Ecosystems?
Reefs host a quarter of marine species but are threatened by warming and acidification.
What will I learn in Coral Reefs and Marine Ecosystems?
Corals live with algae in symbiosis. Bleaching occurs when water is too warm. Reefs protect coasts.
Is Coral Reefs and Marine Ecosystems part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Coral Reefs and Marine Ecosystems lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Coral Reefs and Marine Ecosystems?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.