What are reasons coral reefs are disappearing?

The reasons are; warming waters, pollution, ocean acidification, overfishing, and physical destruction are killing coral reefs around the world.

Can corals protect itself from these pollutants as I have read it can live for 5,000 years?

The coral reef structure acts as buffer and protect shorelines against waves, storms, and floods, helping to prevent loss of life, property damage, and erosion.
In turn, this enhances the clarity and quality of the ocean’s waters. Clean and clear water makes our beaches more beautiful and also allows coral reefs to continue to live longer.