Updated by: Arabinda Naik
The coral reefs grow best at a depth of about 30 metres or less and normally in warm water up to about 20°C. Light and amount of sediment also limit the reef forming corals. They also fail to grow in dark shaded areas, and they completely die in total darkness. Below 50 metres no reef building corals are found though some solitary corals exist up to 8000 metres.
Most coral reefs were created following the Last Glacial Period when rising sea levels from melting ice flooded continental shelves. Most coral reefs are under 10,000 years old. The reefs expanded higher as settlements grew, keeping pace with the sea level rise. Reefs that climbed too slowly could drown if there wasn’t enough light. Coral reefs can also be found in the deep ocean, next to oceanic islands and atolls, distant from continental shelves. Most of these islands were formed by volcanic activity. Others stem from tectonic plate movements that raised the deep ocean floor.
Warm, clear, and shallow water: Coral polyps prefer warm, clear, and shallow waters where sunlight can penetrate and reach the algae that live within them. These algae, called zooxanthellae, provide corals with essential nutrients through photosynthesis. Optimal water temperatures for coral growth range from 73° to 84° Fahrenheit (23° to 29° Celsius).
Salinity: Coral reefs require saline water with salinity levels between 32 to 42 parts per thousand (ppt). This salinity range is crucial for maintaining the physiological processes of coral polyps and their symbiotic algae.
Stable water conditions: Coral reefs are sensitive to sudden changes in water temperature, salinity, and turbidity. Stable water conditions are essential for coral growth and survival.
Limited nutrient runoff: Coral reefs are susceptible to nutrient runoff from land-based sources, such as agriculture and sewage. Excessive nutrient enrichment can lead to algae overgrowth, which can smother corals and disrupt the delicate balance of the reef ecosystem.
Protection from sedimentation: Coral reefs are also vulnerable to sedimentation, which occurs when fine particles like silt and sand settle on the reef surface. Sedimentation can block sunlight from reaching zooxanthellae and can smother coral polyps.
Limited exposure to storms and waves: While some coral species can withstand moderate wave action and storms, prolonged exposure to strong currents and extreme weather events can damage coral reefs and hinder their recovery.