Corals have been deeply frozen or cryopreserved with hopes that the oceanic ecosystems would be preserved.
Coral Cryopreservation
For almost 20 years, cryopreservation has been performed among corals. As part of this procedure, corals were frozen at temperatures that go as low as -196 degrees Celsius for the corals to be kept in the long term. The aim is to plant the corals from cryopreserved samples on coral reefs suffering from acidification and bleaching.
However, progress in these developments has been quite slow. Hence, when a research team could detail a study on how adult corals were grown from cryopreserved larvae, it was a major milestone.
Coral cryopreservation is hard. One reason for this is that thawing and freezing may destroy cells. As the temperature levels are lowered, the water in the cells of the corals freeze, leaving the corals deflated and dehydrated.
The process of reheating is also quite delicate. If the warming up is done too slowly, the ice could refreeze and tear through the outer membranes of the cells. This could lead to a soggy mess as the innards of the cells ooze out through the cells.
However, through trial and error, cryobiologists developed techniques that allowed corals to reach adulthood. Arah Narida, a graduate student from Taiwan's National Sun Yat-sen University, who is part of the research team, notes that to prevent ice damage, the animals are first washed in antifreeze. While antifreeze could be toxic, it seeps into the larvae cells and pushes water out. This allows the corals to live through the next stop of being dunked into nitrogen liquid.
When Narida started the experiments on hood corals in 2021, gold was included in the antifreeze recipe and mixed with other chemicals to reduce the toxicity of the solution. Naria used a laser for welding jewelry to minimize damage and quickly thaw the animals. Afterward, she carefully washed the antifreeze using seawater. This then rehydrated the corals.
As a result, 11% of the experiment's larvae survived the thawing process. They then settled and then grew into adults.
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Saving Coral Reefs
Coral cryobiologist Leandro Godoy from Federal University at Rio Grande do Sul explains being impressed by the number of larvae that survived. Godoy adds that it is a huge step, given how only 5% of corals in the wild end up surviving.
The oldest thawed coral of Narida's team has survived for almost nine months. It is still growing. However, it is necessary to do more work as the larvae that live through the cryopreservation process are remarkably fragile and face side effects that may hamper their development. These larvae require careful maintenance in the Lab.
Godoy explains that the challenge now lies in boosting the survival of the coral to allow large-scale restoration of reefs. Narida admits the need to improve but still considers the efforts a success.
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