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Why does sunlight affect the growth of coral reefs?
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coral reef
The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.
Sunlight is essential for the growth of coral reefs primarily because of the symbiotic relationship between reef-building corals and zooxanthellae, which are photosynthetic, single-celled algae living within the coral's tissues.123
These algae require sunlight to perform photosynthesis, a process that provides several critical benefits for reef development:
- Skeletal Formation: Zooxanthellae accelerate the formation of the coral's calcium carbonate skeleton by rapidly removing carbon dioxide produced during the coral's metabolism.23
- Metabolic Efficiency: By consuming metabolic byproducts like nitrogen, phosphorus, and sulfur, the algae help the coral manage waste that would otherwise be excreted.2
- Growth Requirements: High light intensity and radiant energy are necessary for this coral-algae complex to function effectively and secrete the calcium carbonate matrix that builds the reef.23
Because of this dependence on light for photosynthesis, reef-building corals are restricted to the photic zone, where water depth and clarity allow sufficient light penetration. Factors such as water turbidity can reduce this light, thereby limiting the growth and distribution of the reef.14