You won’t be surprised to read that coral reefs are going through a tough time. It may surprise you to read, however, that scientists have been trying and failing to freeze coral larvae for the past twenty years in an attempt to preserve them, prevent their extinction, and hopefully get to a place where they can be replanted in the oceans in the future.
The cryopreservation process uses liquid nitrogen to freeze rice-sized corals down to -196 Celsius, or -320F. This doesn’t kill the corals outright but it does dehydrate them and damage their delicate cells, so antifreeze is used to push out the larvae’s water, which would otherwise freeze, along with nanoparticles of gold to aid even rewarming.
2018 saw the first breakthrough, where the larvae of the Hood Coral, Stylophora pistillata, survived both the freezing and thawing process, only the larvae went into the free-swimming stage, never settled, and died. Fast forward to 2021 and researchers refined the antifreeze mix ( a solution that can be fatal if ingested by humans,) as well as targeting those nanoparticles of gold and heating them up with a high-powered laser. The result, 11% of the surviving larvae settled and grew on, the oldest of which is now nine months old and can be considered an adult, fully functioning coral. 11% is not to be sniffed at if scaled into the thousands or even millions of frozen larvae, and according to the researchers there is only a 5% successful settlement rate in the oceans right now.
Reefers know that Stylophora is pretty darn hardy as SPS corals go, and it may go some way to explain why S.pistillata is such a popular study animal in coral research. But the fact that we can now captive spawn corals and reef fishes, and cryopreserve coral larvae to reseed the reefs of the future, is a huge step and one that should be celebrated as a milestone in coral reef conservation and restoration.