It was a tragedy so devastating that it took several years for the foraminifera population to recover. Since then, foraminifera have started bleaching in March every year, with peak bleaching near the summer solstice. While Muller's discovery in 1991 was the first time bleaching had been observed in foraminifera, bleaching had been seen in coral several times over the years. Further research began to uncover what was happening. It seems coral and foraminifera bleach because of changes in the Earth's atmosphere, particularly ozone depletion and global warming.
Ozone depletion allows more ultraviolet light to penetrate the clear waters of the coral reefs.
She hypothesizes that algae were damaged by too much ultraviolet light and stopped producing sugars. Once the algae weren't producing sugars, the foraminifera ate them. But algae contribute to the production of calcium carbonate, which makes up the foraminifera's shells, so the shells are more prone to break without algae. According to Muller, Mount Pinatubo's eruption put volcanic ash and aerosol into the stratosphere, which worked with chlorofluorocarbons to destroy ozone. There was about a 4 percent decrease in stratospheric ozone, which likely allowed more ultraviolet light to reach the reefs where coral and foraminifera live.