Coral bleaching is a stress response in corals where they lose their vibrant colors and turn white due to the expulsion of symbiotic algae called zooxanthellae that live within their tissues. These algae provide corals with nutrients through photosynthesis and give them their coloration. When corals are stressed-most commonly by elevated water temperatures-they expel these algae, causing the coral tissue to become transparent and reveal the white calcium carbonate skeleton underneath, hence the term "bleaching"

. The primary cause of coral bleaching is rising ocean temperatures linked to climate change, which leads to heat stress. Other stressors include changes in water quality, pollution, overexposure to sunlight, freshwater runoff, and chemical contaminants. These factors disrupt the coral-algae symbiosis, sometimes causing the algae to produce toxic reactive oxygen species, prompting their expulsion by the coral

. Bleached corals are not dead but are severely stressed and more vulnerable to starvation and disease because they lose up to 90% of their energy source when the algae leave. If stressful conditions persist, corals may die, leading to reef degradation. However, if conditions improve, corals can sometimes recover by reabsorbing the algae

. In summary, coral bleaching is a visible sign of coral stress primarily caused by environmental changes, especially warming waters, that disrupt the vital relationship between corals and their symbiotic algae, threatening coral reef ecosystems worldwide