Frozen Sperm Offer a Lifeline for Coral

Andrew Heyward/Australian Institute of Marine Science

SPAWNING An Acropora tenuis coral releasing sperm, an annual event. Scientists are freezing coral eggs and sperm that may be used to restore reefs.

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.

Source: http://feeds.nytimes.com/click.phdo?i=5aa793f1f9276d17b1c8db96ee019ec3

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