— Ch. 1 · Symbiotic Breakdown Mechanism —
Coral bleaching.
~4 min read · Ch. 1 of 7
In 1985, a coral polyp in the Great Barrier Reef expelled its microscopic algae partners when water temperatures rose just one degree above average. This expulsion triggered a chain reaction where the coral lost up to 90 percent of its energy supply. The zooxanthellae, which live inside the coral tissue, produce reactive oxygen species that become toxic to their host when heat increases. To survive this immediate threat, the coral pushes these algae out through its skin. Without the algae, the transparent tissue reveals the white calcium carbonate skeleton beneath. Some corals appear blue or pink instead of white due to intrinsic pigment proteins, but they remain vulnerable to starvation and disease.
Climate Change Drivers
The ocean absorbed a large portion of carbon dioxide emissions from human activity starting in the early 20th century. This absorption changed seawater chemistry by lowering pH levels, creating conditions never seen before in Earth's history. A temperature increase of about 1°C or 2°F above average can trigger bleaching events globally. Marine heatwaves caused by El Niño-Southern Oscillation have been identified as main causes of widespread coral mortality since the late 1970s. The Intergovernmental Panel on Climate Change reported in 2022 that mass bleaching frequency has increased sharply worldwide since the early 1980s. Ocean acidification reduces the amount of carbonate ions available for building skeletons, making reefs more susceptible to erosion and collapse.