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| Bleached coral reef |
By Michelle Nijhuis, The New York Times, July 23, 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.”
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