B4.1.5—Coral reef formation conditions

Coral reef formation depends on warm, shallow, clear, sunlit, saline water and is limited by temperature, light, pH and carbon dioxide.

Exam analysis

Chance of appearing1%of analysed past papers

Latest appearanceMay 2017

Most common paperPaper3

Typical marks1

Common command terms

Outline
Describe
State

Scoring notes

Common mistake: Saying higher temperature alone proves coral decline without acknowledging correlation limits.

Recent exam appearances

May 2017Paper3 ["SL"] · TZ113(c)[ 1 ]B4.1.5—Coral reef formation conditions

Coverage 2017–2017 · Updated 15 Jul 2026

Reef-building corals depend on warm, shallow, clear, well-lit seawater with suitable salinity and carbonate chemistry. Photosynthetic symbionts supply much of the energy supporting calcification.

Coral reef system diagram showing shallow sunlit water, coral polyps with zooxanthellae, clear water column, saline seawater, and side arrows indicating limiting factors such as sediment, reduced light, cold upwelling, and lower pH.

greater depth or turbidity → less light
thermal stress → bleaching risk
lower pH → harder CaCO₃ deposition
sediment/nutrient disturbance → damaged or shaded coral

measure environment → locate tolerance limits and optimum → predict possible distribution → test abundance in the field → explain how adaptations change performance

microhabitat: local moisture, light and temperature
species range: interacting tolerance, adaptation and dispersal limits
biome: long-term climate filters whole communities; similar pressures can produce convergent forms

[ 2 ]

Outline one way in which reef-building corals are affected by increasing atmospheric carbon dioxide.

Concept essentials

Reef-building corals need light because their zooxanthellae photosynthesise.
Calcium carbonate skeleton formation is affected by pH and carbonate availability.
High temperature can cause coral bleaching through loss of zooxanthellae.
Temperature, light, salinity, carbon dioxide and pH can limit reef formation.