Which of the following factors are needed for the growth of corals? 1. Freshwater 2. Clear shallow salt water 3. Plenty of sunlight for photosynthesis 4. Warm water between 23°C and 25°C Select the correct answer using the code given below.

Coral reefs require specific environmental conditions for optimal growth. They thrive in clear, shallow salt water, typically at depths not exceeding 50–60 meters, to ensure maximum sunlight penetration [3]. This light is vital for the photosynthetic activities of symbiotic zooxanthellae algae, which provide corals with essential nutrients and energy [4]. Regarding temperature, reef-building corals are generally confined to tropical waters, growing optimally between 23°C and 29°C; they cannot tolerate temperatures below 18°C [3]. While corals require saline water (32–42 parts per thousand), freshwater is actually detrimental to their growth [3]. Large influxes of freshwater from rivers or heavy rainfall can lower salinity levels and increase sedimentation, both of which stress or kill coral polyps. Therefore, factors 2, 3, and 4 are necessary, while factor 1 (freshwater) is a limiting or harmful factor.

Sources

1. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 11: Islands and Coral Reefs > Coral Reefs > p. 99
2. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.9. CORAL REEFS > p. 50
3. [4] https://www.sciencedirect.com/science/article/abs/pii/S0272771410001952