If kelp became over abundant in reefs, then it would overrun the coral. This would cause sediment to spread causing the water to become murky and unclear. Then the algae that grow on the coral will die off, slowly causing higher parts of the food chain to die. Therefore, keeping everything in this ecosystem balanced is very important.
Density-independent factors include natural disasters and pollution. An oil leak can just as easily destroy a coral reef ecosystem as a hurricane can. If the water the coral reef is inhabiting begins to get too cold, then that coral reef will die off due to it being only able to survive in warm tropical waters.
Because of how the coral continues to build and form on rocks, limestone, and skeletons of animals, a coral reef is considered to be secondary succession.