Which process causes coral colonies to lose their color?

Coral bleaching is the process responsible for causing coral colonies to lose their color. This phenomenon occurs when stressed corals expel the symbiotic algae called zooxanthellae that live within their tissues. These algae provide corals with essential nutrients through photosynthesis and give them their vibrant colors. When corals are exposed to stressful conditions such as elevated water temperatures, pollution, or changes in pH levels, they may react by expelling these algae. As a result, the corals turn white or lose their color, a condition known as bleaching. If the stress persists, it can lead to coral death, as the corals become deprived of the nutrition the algae supply.

Coral fragmentation, reproduction, and regeneration describe processes related to coral growth and reproduction but do not involve the loss of color in corals. Fragmentation is a method by which corals can reproduce asexually, while reproduction can refer to both sexual and asexual methods of producing new coral organisms. Regeneration entails the ability of corals to recover and regrow damaged areas after disturbances. Therefore, these processes do not connect to the phenomenon of color loss, making coral bleaching the correct answer.