What can warming ocean waters cause coral reefs to do?

Warming ocean waters primarily cause coral reefs to bleach. Coral bleaching occurs when corals, under stress from increased temperature, expel the symbiotic algae (zooxanthellae) that live in their tissues. These algae provide essential nutrients and are responsible for the vibrant colors of coral reefs. When corals lose these algae due to stress, they turn white or "bleach," which can lead to a decline in health and increase susceptibility to diseases. This process disrupts the relationship between the coral and the algae, ultimately endangering the reef ecosystem and the diverse marine life it supports.

In contrast to bleaching, the other options suggest positive responses by the coral reefs to warming waters, which is not accurate in the context of rising temperatures.