Which of the following are the necessary conditions for the growth of coral reefs ? 1. Photic conditions 2. Clean and sediment free water 3. Sea salinity of 6% 4. Tropical sea water with temperature of 20DC to 21°C Select the correct answer using the code given below :

Coral reefs require specific environmental conditions for survival. Statement 1 is correct as corals need photic conditions (light) for the photosynthesis of symbiotic zooxanthellae, typically restricting growth to the upper 30 meters [2]. Statement 2 is correct because sediment-free, clear water is essential; silt can smother polyps and block sunlight [3]. Statement 4 is correct as reef-building corals thrive in tropical waters where temperatures do not fall below 20°C to 21°C [3]. However, statement 3 is incorrect; corals require high salinity, but the optimal range is approximately 32 to 42 parts per thousand (3.2% to 4.2%), not 6% [1]. A salinity of 6% (60 parts per thousand) would be too hypersaline for most coral species. Therefore, only conditions 1, 2, and 4 are necessary and accurate.

Sources

1. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 4: BIODIVERSITY > corAl reefs. > p. 54
2. [3] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 11: Islands and Coral Reefs > Sample Objective O,uestions > p. 103
3. [1] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 11: Islands and Coral Reefs > Coral Reefs > p. 99