Coral Bleaching Captured On Video As Algae Are Violently Ejected

Rising ocean temperatures have led to large-scale bleaching of corals along the Great Barrier Reef, where over 90 percent of reefs have already been affected by bleaching. And now, scientists at Queensland University of Technology (QUT) in Australia have managed to film the behavior of a coral as it was bleaching under stress.

Corals themselves are white but look colorful because they house a large number of algae that give the corals their vibrant colors. They live in a symbiotic relationship, with the coral providing the algae a place to stay and feeding off the sugar the algae produce.

However, as the temperature of water begins to rise, the algae become toxic to the coral. If the high temperatures continue for a long period of time, the coral is forced to eject the algae from its body, an action that causes it to turn white and therefore called bleaching.

In the video, each of the spasms of the coral throws up a colored cloud, which is actually the algae being forcefully removed from it. To see the coral’s behavior under stress caused by high temperature, Brett Lewis and Luke Nothdurft from QUT placed solitary corals, Heliofungia actiniformis, into a regulated aquarium system. They then increased the temperature of the water in the aquarium system from 26 degrees Celsius to 32 degrees Celsius (78.8 degrees Fahrenheit to 89.6 degrees Fahrenheit) over a period of 12 hours and left it at that for up to eight days.

“What’s really interesting is just how quickly and violently the coral forcefully evicted its resident symbionts,” Lewis, who is from QUT’s Science and Engineering Faculty, said in a statement on the university’s website. “The H. actiniformis began ejecting the symbionts within the first two hours of us raising the water temperature of the system.”

Observing the phenomenon was significant because “H. actiniformis was one of the very few corals on the Great Barrier Reef considered to be relatively resilient to bleaching, even as neighbouring species suffered the full effects.” And according to Nothdurft, who is from QUT’s School of Earth, Environmental and Biological Sciences, some corals may regain the algae and their associated colors if environmental conditions returned to normal quickly.

“If the Symbiodinium is removed from the host and does not recolonise quickly, the corals can die,” Nothdurft said in the statement.