A Sperm Bank for Coral Reefs

An example of a coral spawning, in this case, the species Orbicella faveolata, or mountainous star coral. Credit: Schmahl/FGBNMS

Ocean health matters to us, and the state of our corals is one of the most at-risk elements of marine ecosystems. So many species depend on coastal communities of these strange lifeforms, and with acidification and pollution of sea waters, the reefs are in danger of slowly but surely dying out. Thankfully, there are efforts underway to conserve coral in an unusual way – freezing and storing their sperm. Julie Liebach reports for Science Friday:

You’ve heard of seed banks—precious vaults that keep plant genetic material frozen for posterity’s sake. But what about coral banks?

For more than a decade, marine biologist Mary Hagedorn has been cultivating the art of carefully freezing coral sperm through a process known as cryopreservation. Her goal is to bank as many species as possible for use in future research and restoration, and to train other scientists to follow her lead.

“We need to be gathering this genetic diversity and trying to help while there’s still a lot of diversity in place in the ocean,” says Hagedorn, a senior research scientist at the Smithsonian Conservation Biology Institute, who’s based in Kaneohe, Hawaii.

The world’s coral faces an onslaught of threats, both local—such as pollution and sediment buildup—and global, like increasing ocean temperatures and acidity levels stemming from rising greenhouse gas emissions.

Coral bleaching is one particularly noticeable manifestation of coral stress that only stands to intensify with the changing climate. It happens when unusually high or low water temperature causes coral to expel the symbiotic algae that provide them with nutrients.

“We’re seeing devastating changes in our reefs because of the bleaching,” says Hagedorn. “It stresses them, and it stresses them to the point where many of them do not reproduce, and it can stress them to the point where they [could] die.”

Case in point: Aerial and underwater surveys taken by Australia’s National Coral Bleaching Taskforce reveal that bleaching has affected 93 percent of the Great Barrier Reef, to at least some degree. Areas hardest hit—in the reef’s northern reaches—have suffered a 50-percent die-off, according to a preliminary release on the findings.

Freezing coral gametes in banks for safekeeping could potentially help researchers and conservationists cope with, and counter, the loss of coral diversity in the wild. The idea is that scientists would be able to draw on these “frozen zoos,” as Hagedorn calls them, for material for use in various types of coral research, such as improving techniques for rearing and restoring coral to reefs.

Because many corals have limited spawning periods, banks also offer greater access to experimental material that would otherwise be obtainable only a few times a year.

Hagedorn had been researching cryopreservation in fish when she became interested in the plight of corals. Developing and fine-tuning a procedure to safely freeze and store their sperm has consumed more than a decade. “It is not a cookbook process,” Hagedorn says. “It took me several years to figure out exactly how to cryopreserve coral sperm, and how to make the freezing process simple and field-friendly so that we could bank under field conditions.” She successfully banked her first sperm about five or six years ago.

Generally, preparing coral sperm for banking involves gathering coral fragments or colonies on the verge of spawning (many corals are hermaphrodites; each polyp contains ovaries and testes); placing them in individual containers submerged in seawater; and waiting for them to release their egg and sperm together in ethereal bundles, which float upwards like millions of tiny balloons.

“It’s the most beautiful thing on earth, honestly,” Hagedorn says dreamily.

Researchers standing at the ready suck up the bundles with pipettes and place them into tubes of seawater. The packages eventually fall apart, with the eggs floating to the surface and the sperm remaining in solution. Then “we create sort of a mini fertility clinic for the corals,” says Hagedorn.

Read the rest of the article here.

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