When corals turn white, they are starving for survival

Science · Published 27 October 2026 Swipe more like this →

In short: Coral bleaching is often mistaken for death, but it is actually a desperate biological divorce. When conditions become too harsh, corals expel the microscopic algae that provide their food and color. This leaves the coral white, vulnerable, and struggling to survive in a rapidly changing ocean.

Corals maintain a vital symbiotic relationship with microscopic algae called zooxanthellae. These algae live within the coral's tissues, providing the coral's primary food source through photosynthesis while also giving the reef its vibrant colors. However, this partnership is delicate. When corals are stressed by environmental factors—most notably increased ocean temperatures caused by climate change—the zooxanthellae begin to produce toxic reactive oxygen species. These molecules are harmful to both the algae and the coral host, forcing the coral to physically expel the algae from its tissues.

Once the algae are gone, the coral loses its main energy source and turns white or very pale. While a bleached coral is not immediately dead, it is in a state of extreme stress and becomes highly susceptible to disease. If the stress persists and the algae do not recolonize the coral within a few months, the individual coral and its entire colony will eventually die. While warm water is the leading cause of bleaching, other factors can trigger the same response, including pollution, high solar irradiance, sediment buildup, and even extreme cold water temperatures, which dropped 6.7 degrees Celsius below typical levels in the Florida Keys in 2010.

The consequences of this breakdown extend far beyond the reef itself. Coral reefs are the foundation for approximately 25 percent of all marine species, providing essential shelter and spawning grounds for thousands of animals. When reefs collapse, biodiversity drops precipitously, threatening the food security and livelihoods of humans who rely on these ecosystems for protein and tourism. Furthermore, reefs act as natural barriers against storm surges; their loss leaves coastal communities vulnerable to the full force of the ocean.

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