Researchers have made a surprising discovery – coral bleaching occurring at depths where corals were previously protected from the warming effects at the ocean’s surface.
Typically, when ocean temperatures rise, corals expel the algae living in their tissues, resulting in a bleached appearance. While the algae can regain their color if temperatures cool, prolonged high temperatures can be deadly. Climate change has led to routine bleaching events in shallow reefs around the world, from Australia to the Caribbean.
Scientists had previously believed that deeper reefs were safe from warming. However, in 2019, coral bleaching was observed at a depth of 300 feet in the Egmont Atoll in the Indian Ocean. This bleaching event affected 80 percent of the corals in some areas. The findings were recently published in Nature Communications.
“This is a huge surprise,” said Philip Hosegood, coauthor of the study and an oceanographer at the University of Plymouth in the UK. “Deeper corals were thought to be resilient to ocean warming due to cooler water temperatures compared to the surface.”
The warming of the waters around the Egmont Atoll was attributed to an El Niño-like phenomenon in the Indian Ocean, causing alternating warm and cold conditions. Climate change exacerbated the already elevated temperatures. Researchers returned to the site in 2020 and 2022 and found that much of the reef had recovered, but they remain concerned about the future of coral reefs worldwide. “Reefs at similar depths around the world are likely at risk from similar climatic changes,” added Hosegood.
