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Michelle Nijhuis

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Frozen Sperm Offer a Lifeline for Coral

Michelle Nijhuis
October 23, 2012

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Acropora palmata spawning in Belize, courtesy of Raphael Ritson-Williams.
Acropora palmata spawning in Belize, courtesy of Raphael Ritson-Williams.

Alicia Patterson Report 3 – 2011 Fellowship

A version of this story appeared in The New York Times on July 24, 2012.

COCONUT ISLAND, Hawaii — Just before sunset, on the campus of the Hawaii Institute of Marine Biology, Mary Hagedorn waited for her mushroom corals to spawn.

As corals go, Fungia is fairly reliable, usually releasing its sperm and eggs two days after the full moon. Today was Day 3. “Sometimes we get skunked,” she fretted.

The recalcitrant corals sat outdoors in water-filled glass dishes, arranged in rows on a steel lab table. Each was about the size and shape of a portobello mushroom cap, with a sunburst of brown ribs radiating from a pink, tightly sealed mouth.

As Dr. Hagedorn and her assistant watched, one coral tightened its mouth and seemed to exhale, propelling a cloud of sperm into its bath with surprising vigor. The water bubbled like hot oatmeal.

A reproductive physiologist with the Smithsonian Institution, Dr. Hagedorn, 57, is building what is essentially a sperm bank for the world’s corals. She hopes her collection — gathered in recent years from corals in Hawaii, the Caribbean and Australia — will someday be used to restore and even rebuild damaged reefs.

She estimates that she has frozen one trillion coral sperm, enough to fertilize 500 million to one billion eggs. In addition, there are three billion frozen embryonic cells; some have characteristics of stem cells, meaning they may have the potential to grow into adult corals.

Relative to the number of corals in the ocean, Dr. Hagedorn’s collection — stored in her laboratory and several zoo repositories — is tiny. But so far, it is the only one of its kind.
While corals can reproduce asexually — that is, fragments of coral can grow into clones of their parents — Dr. Hagedorn points out that only sexual reproduction maintains genetic diversity within populations, and with it a species’ capacity to survive and adapt to change. For corals, the number of likely partners is shrinking: As climate change warms the oceans, corals are becoming more vulnerable to disease — and to bleaching, a condition in which stressed coral expel the colorful algae critical to their food supply.

In recent years, bleaching events have grown from local curiosities to global phenomena, and in some cases are so severe and long-lasting that the corals cannot recover. Meanwhile, rising levels of carbon dioxide are acidifying the oceans, inhibiting the growth of coral skeletons and slowly weakening the calcium-carbonate bones of reefs worldwide.

In the Caribbean, high water temperatures, disease outbreaks, overfishing and other afflictions have already killed 80 percent of the region’s coral, reducing many reefs to seaweed and rubble. A similar constellation of problems is killing coral in the Pacific, and in the central and western parts of that ocean the extent of living coral is thought to have shrunk by half between the early 1980s and 2003.

If this decline continues, almost all of the world’s reefs will be on their way to oblivion by 2050. An estimated one-fourth of all known marine species have some association with coral reefs; some may be able to survive on seaweed, but not all. This month, researchers at the International Coral Reef Symposium in Cairns, Australia, summed up the situation: “Together, this combination of climate-related stressors represents an unprecedented challenge for the future of coral reefs and to the services they provide to people.”

For marine scientists whose careers depend on coral reefs, Dr. Hagedorn’s collection can be reassuring. “Mary is my insurance policy,” said Greta Aeby, a biologist who works in a dockside laboratory on Coconut Island and studies coral disease throughout the Pacific.

“We’re working as quickly as we can,” she added, “but it’s not enough. I keep telling my students, ‘Study faster!’ ”

For decades, conservationists have worked to protect reefs with marine reserves, fishing regulations and other measures. Despite some high-profile successes, just 27 percent of the world’s reefs lie within reserves, and reserve enforcement is spotty at best. As the pressures of climate change increase, even the sunniest marine biologists say the future of coral reefs relies on refuges, or refugia — places where local threats are minimal, or where the corals are biologically more adaptable to the pressures of climate change.

Though Dr. Hagedorn supports these traditional conservation strategies, she is preparing for their failure. While she freezes coral sperm and eggs for future use, colleagues are refining techniques for raising coral in captivity and for reintroducing young corals to their natural habitats.

But she and her colleagues have to struggle to raise money for her efforts, which are often seen as a distraction from the more immediate job of habitat protection. “In an ideal world, we would do both,” said Stephen Palumbi, director of the Stanford University Hopkins Marine Station. “Of course, in an ideal world, there would be no funding constraints.”

Still, both strategies may ultimately be necessary. “Protecting fish communities, making sure water quality is good, all of those efforts can buy decades of time,” said Nancy Knowlton, a prominent coral-reef biologist at the Smithsonian. “But if we continue on this greenhouse-gas emissions trajectory, the only place we’re going to be able to find many corals will be in Mary’s freezers.”

Since 1949, when the British biologist Christopher Polge successfully froze and thawed a vial of rooster sperm, scientists have deployed the technique in dozens of species, including humans, pigs, oysters and bumblebees. Yet every species is different in its sperm’s response to freezing, and mastering so-called cryopreservation for a single species can take years of experiments.

Eggs and embryos, because of their much larger size, are even more difficult to preserve. “Sometimes the next step is getting punched repeatedly in the face,” said Kenneth Storey, a cryopreservation researcher at Carleton University in Ottawa. “This is hard work, hard empirical work. It’s uphill.”

In her work in Hawaii and elsewhere, Dr. Hagedorn has encountered not just those frustrations but also the quirky, mysterious nature of corals. Simultaneously animal, vegetable and mineral, corals are colonies of simple creatures called polyps, housed in the distinctive calcium-carbonate sculptures that form coral reefs.

Coral sex is poorly understood: The periodic broadcast spawns of coral sperm and eggs were essentially unknown to scientists until the early 1980s, when a team of Australian researchers on a nighttime dive began to encounter upside-down blizzards of spawn. Researchers are still unsure why so many spawns are tied to phases of the moon.

Like the Fungia on the campus of the Hawaii Institute of Marine Biology, corals sometimes stray from their expected spawning schedules, and Dr. Hagedorn has spent anxious evenings on shore in Puerto Rico and Belize, waiting for endangered corals to begin their yearly spawn in the open water.

But luck was with her last fall, when she and a group of colleagues traveled to Australia at the invitation of the Australian Institute of Marine Science. Using techniques developed by Dr. Hagedorn, they collected and froze sperm and cells from colonies of Acropora tenuis and Acropora millepora, two of the roughly 400 coral species native to the Great Barrier Reef.

The coral cells and sperm are now stored in liquid nitrogen at the Taronga Western Plains Zoo in New South Wales, alongside frozen sperm samples from koalas, yellow-footed rock wallabies and dugongs.

In 2009, JoGayle Howard, a National Zoo researcher known as the “sperm queen,” produced healthy black-footed ferret kits by inseminating a female ferret with sperm collected and frozen more than 20 years earlier, adding valuable genetic diversity to the endangered species. Dr. Howard, who died in 2011, remains an inspiration to Dr. Hagedorn: When her work is interrupted by tropical weather or the vagaries of coral spawns, she likes to remember that even one vial of frozen sperm could be worth all the trouble.

“Think about the black-footed ferret,” she said. “Just a few individuals can get a population started again.”

© 2011 Michelle Nijhuis