Rising ocean temperatures have prompted devastating coral bleaching in Australia’s Great Barrier Reef – and in some sections, at least 35 percent of bleached coral has died. Now scientists at the Queensland University of Technology (QUT) have scrutinized just how coral reacts to hotter temperatures in controlled conditions, and caught the process on film.
Scientists Brett Lewis and Luke Nothdurft put Heliofungia actiniformis coral in a 10 liter “aquarium system” to see how the coral would respond as they heated the water. Over 12 hours, they increased water temperatures from 26 degrees Celsius to 32 degrees Celsius, or about 78.8 degrees Fahrenheit up to 89.6 degrees Fahrenheit. They kept the coral in the system for around eight days.
The coral spewed Symbiodinium algae that live in them and provide the brilliant colors we’re used to seeing in coral reefs. The algae also generate sugars consumed by the coral. Expelling algae under the duress of hot temperatures can help the coral to survive – Lewis said “rapid expulsion” could increase the coral’s chance of survival. It’s possible for coral to regain the algae and their vivid colors if conditions improve, but if ocean temperatures don’t return to normal levels and the algae doesn’t recolonize, the coral can die. Scientists have been aware of this expulsion process, but the QUT team’s video is the first to show the eviction in action.
Lewis said in a press release, “What’s really interesting is just how quickly and violently the coral forcefully evicted its resident symbionts. The H. actiniformis began ejecting the symbionts within the first two hours of us raising the water temperature of the system.” Northdurft said coral bleaching is a “concern for scientists globally.”
The journal Coral Reefs published their research online earlier this month.