Final answer:
Corals bleach due to the expulsion of symbiotic algae caused by rising ocean temperatures and increased atmospheric carbon dioxide leading to higher ocean acidity. This leads to coral stress, color loss, and potential death, affecting biodiversity and economies.
Step-by-step explanation:
Corals bleach and lose their pinkish color in response to stressful conditions primarily due to the expulsion of symbiotic algae. These symbiotic algae, known as zooxanthellae, have a mutualistic relationship with the coral, providing it with much of the energy it needs through photosynthesis. When ocean water temperature rises due to climate change and global warming, corals become stressed and expel these algae, leading to bleaching. This loss of algae deprives the coral of color and vital nutrients, which can result in the death of the coral if the zooxanthellae are not regained. Additionally, higher levels of atmospheric carbon dioxide lead to increased ocean acidity, which interferes with the coral's ability to calcify, further contributing to the coral's stress and potential mortality. The decline and death of coral reefs have significant implications for biodiversity, ecosystem services, and local economies.