What is the main factor allowing corals to thrive in certain depths?

Corals primarily thrive in shallow waters due to the availability of sunlight, which is essential for their growth and health. Corals have a symbiotic relationship with photosynthetic algae called zooxanthellae, which live within their tissues. These algae require sunlight to carry out photosynthesis, producing nutrients that both the algae and the corals use for energy.

In deeper waters, the intensity of sunlight diminishes rapidly, limiting the depth at which coral reefs can grow. Most reef-building corals are found in depths less than 60 meters (around 200 feet) because beyond this depth, insufficient sunlight hampers the photosynthesis process necessary for coral survival and growth.

While factors like salinity levels, temperature stability, and water pressure do play roles in the broader habitat conditions where corals are found, they are not the primary limiting factors compared to the availability of sunlight. For instance, corals can adapt to various salinities within acceptable ranges and can withstand a range of temperature changes. However, the crucial dependence on light for photosynthesis makes the availability of sunlight the main factor in determining the depth at which corals can thrive.