Final answer:
Coral bleaching is caused by high ocean water temperatures, often due to climate change, leading to the expulsion of symbiotic algae from coral, which can result in significant ecosystem disruption.
Step-by-step explanation:
Bleaching due to high temperatures causes the coral to expel algae. This process is particularly damaging to coral reefs as it disrupts the symbiotic relationship between corals and their algae, known as zooxanthellae. The algae provide corals with food through photosynthesis, and in return, the corals provide the algae with a protected environment and access to light. However, when ocean water temperature rises, often due to climate change and global warming, corals become stressed and expel their symbiotic algae, leading to the loss of their vibrant colors in an event known as coral bleaching. Coral bleaching not only affects the corals themselves but also the entire ecosystem, as many marine species depend on coral reefs for food and shelter. Furthermore, rising levels of atmospheric CO2 contribute to ocean acidification, which interferes with the coral's ability to calcify and build their calcium carbonate skeletons.