For six weeks over this past summer, Mary Hagedorn waited on the island of Curaçao for the one night a year that elkhorn coral — a large branching coral that resembles elk antlers — spawn. Finally, as summer spilled into September, the environmentally threatened coral released vast clouds of egg and sperm bundles. Hagedorn had what she was waiting for: fresh coral eggs to crossbreed with 10-year-old cryopreserved, or frozen, sperm.

Hagedorn is an adjunct professor at the Hawaii Institute of Marine Biology and a research scientist with the Smithsonian Conservation Biology Institute. She has made a name for herself for creating the field of coral cryobiology, the practice of studying how coral cells respond at cold temperatures, and exploring whether freezing coral with liquid nitrogen could help preserve and expand endangered or threatened coral populations. Hagedorn is also helping to create the first genome repository for coral sperm. Her goal in Curaçao was to crossbreed 10-year-old sperm with fresh eggs collected from the western Caribbean to determine whether frozen coral sperm from one area of the Caribbean could be thawed and crossed with coral eggs of the same species in another area.

Cryobiology was once the stuff of futuristic movies. Today, it may be what saves coral reefs of the future. In October, the United Nation’s Intergovernmental Panel on Climate Change released a special report predicting a 70 to 90 percent loss of coral reefs around the world due to climate change. This is significant, because coral reefs are home to more than a quarter of all marine life at some point in their life cycle, including many of the fish species we eat.

Medium spoke with Hagedorn and postdoctoral fellow Jonathan Daly, who assists her research.

Medium: Let’s start with the basics. Why is coral cryobiology important?

Mary Hagedorn: Coral cryobiology can freeze and store the [living cells] of threatened reef areas. Then, this material can be thawed and used to reinvigorate damaged populations or reseed the oceans of the future.

Elkhorn coral was once quite abundant throughout the Caribbean, but now it’s one of the most threatened corals. How could cryobiology be used to recover it?

Hagedorn: Coral spawn only a few nights each year and only a few hours each night. Therefore, we are quite restricted in the time available to study and understand how coral cells might respond to various cryobiological procedures. One of these is called assisted gene flow, whereby [coral] genes from other areas might enhance the survival of a remote population of the same species. Assisted gene flow has already been proven to work in some coral populations between the Northern and Central Great Barrier Reef coral. However, [in that case] they actually moved the colonies, so they crossed fresh eggs and sperm from the two regions. We are developing the tools for assisted gene flow by moving frozen sperm. This is important because as populations fragment, they may no longer spawn on the same nights, thus causing more isolation and loss of genetic diversity. This has already happened for the threatened elkhorn populations in the Florida Keys.

So you finally got your fresh eggs to cross with your 10-year-old cryopreserved sperm in Curaçao?

Hagedorn: It was a very, very long process, because it was a split spawn, which means there were two full moons in August. When that happens, usually the corals will spawn both times. Maybe one time is better than the other, but you’ll get material both times. In Curaçao, that didn’t happen. In fact, they didn’t spawn until the very last day, and we waited six weeks. It was brutal. I was the shore person, but I was so sorry for my colleagues who were diving every single night for six weeks.

Does this mean you’ll be releasing these coral crosses into low-abundance areas of elkhorn coral?

Hagedorn: That might not be allowed to happen right away. There are very strict permitting issues. I don’t know the answer. Our job is to prove the science, to test fertilization with cryopreserved sperm. Then, our next step is talking to the managers. We have a meeting in December to talk about our results and see what we do from there.

Realistically, how quickly can we expect to see cryopreserved corals used in coral reef conservation practices?

Hagedorn: Right now, we are trying to get a myriad of moving pieces to work together, such as banking the sperm, moving these frozen cells to the correct location, getting permits for this work, getting the fresh eggs needed for this work — [which means] long weeks waiting for coral populations to spawn — assessing and fertilizing the eggs with the frozen and thawed sperm, rearing the larvae, inducing settlement, and rearing the settlers. This process is years in the making.

Is there any hope of corals naturally adapting to warming seas?

Jonathan Daly: We can look at coral here in Kaneohe Bay, Hawaii, for some answers. In 1970, Paul Jokiel, at the Hawaii Institute of Marine Biology, brought five species into captivity and exposed them to elevated temperatures. About 80 percent of the coral died. Recently, this same experiment was repeated with the same tanks, the same species, and the same temperature stress profiles, but more than 40 years later. Amazingly, 80 percent of the coral lived. Clearly, given enough time, coral can adapt to some changes in ocean temperature. It is rapid and repeated warming events that are most damaging to coral populations, because warming disrupts reproduction. Without reproduction, adaptation does not take place.

What’s next?

Hagedorn: We will be focusing on several areas over the next few years. One, developing the preservation methods for small fragments of coral so that we are no longer always limited by coral reproduction. If successful, these “microfragments” could be frozen throughout the year and then could be thawed and used to rapidly create new corals. These could be reared in captivity or placed back out on reefs once the appropriate permits are available.

Two, developing “high-throughput” techniques. To date, the cryopreservation processes, like the embryo freezing, produce only hundreds of frozen and thawed larvae at the end of the day. To be a successful restoration technique, we must produce hundreds of thousands in a few hours. This requires faster and more mechanized processes for freezing and thawing.

Three, developing more robust and distributed wildlife banks around the world, and possibly in space, that can safely maintain coral material for one year to tens or hundreds of years.

Coral in space?

Hagedorn: We have a lot to do before we are ready to store cryopreserved material safely in space, but we need a similar type of storage as we have for seeds in the Svalbard [Global Seed Vault]. Various locations in space may allow us to safely store cryopreserved material at minus 196 degrees Celsius. We would need to develop sufficient protection for the biomaterial to protect it from damaging radiation.