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Caring for Coral

Smithsonian's National Zoo scientsts rally to collect, breed, and protect threatened coral

by Dan Stone

Once a year, part of the ocean near Rincon, Puerto Rico, experiences an underwater blizzard. It happens at night, four days after the first full moon in August. Just 15 feet offshore, hundreds of elkhorn coral (Acropora palmata) release thousands of tiny white bundles into the water. This submerged hailstorm of reproductive material is a natural phenomenon few people will ever get to see.

National Zoo marine biologist Mary Hagedorn and invertebrate keeper Mike Henley are two of the lucky ones. Together with a group of scientists, they have traveled to Rincon over the last few years to scuba dive and collect the tiny gametes, or egg-sperm bundles, while the coral spawned. “The white bundles were everywhere—I could barely see a few feet in front of my face,” Henley says. “I’ve never seen anything like it.”

Hagedorn and Henley’s work in Rincon is part of a program called SECORE (SExual COral REproduction, www.secore.org), which was initiated by the Rotterdam Zoo in the Netherlands. SECORE was set up to study coral sexual reproduction and to develop breeding techniques that can be shared by wildlife organizations around the world.

scuba diving in Caribbean
Elkhorn coral are a primary focus of the National Zoo's coral conservation efforts. (Mike Henley/NZP)

Coral and People

“Coral reefs are some of the oldest and most diverse ecosystems on the planet,” says Hagedorn. “Although they cover less than one percent of Earth’s surface, one-fourth of all marine life depends on them.” But more than wildlife relies on reefs; people do, too. Across the globe, millions depend on reefs for food. Ten percent of the world’s fish harvest and 25 percent of developing countries’ fish come from reefs.

Reefs provide other services as well, such as protection from storms and erosion. Equally important, reefs are a source of potential antibiotics and medicines. Chemicals from a Caribbean sponge are used to create the HIV-AIDS drug azidothymidine, or AZT. Reefs also offer a sanctuary to snorklers and scuba divers, who are drawn to their beauty and magnificence.

“Reefs are the rainforests of the sea, and coral are like the trees,” says Henley. “But the difference is that rainforests are plant-based ecosystems, while reefs are animal-based ecosystems. After all, coral are animals.”

Local Impacts on Reefs

Despite their critical role in aquatic ecosystems and human survival, coral are disappearing all over the world. A number of scientists predict that some coral species may become extinct within ten to 30 years. Both local and global stressors are having a negative impact on coral reefs. “One problem is the local abuse of reefs, which includes people stepping or walking on reefs,” says Hagedorn. “And in some places they actually use dynamite to blow up the reef to hunt for fish. Coral doesn’t recover well from these kinds of abuses.”

Coral's brilliant coloring is thanks to zooxanthellae, a type of algae (Mehgan Murphy/NZP)

Another threat is sedimentation, which results from poor land-use practices such as deforestation from coastal construction projects. During construction, forests of mangroves and other fauna are wiped out, permitting sedimentation and other runoff to enter the sea. When the soil settles on a reef, it can smother coral by blocking out sunlight. This causes the coral to bleach—a visible sign of poor health.

Coral will bleach, or turn a white color, when something harms the tiny, microscopic algae called zooxanthellae (pronounced zoo-ZAN-thell-ay) that live within healthy coral (see “Mighty Microscopic”). These algae live in a symbiotic relationship with coral and give them food and their brilliant colors. In turn, coral provide zooxanthellae with protection and vital nutrients. If the zooxanthellae lose access to sunlight, they stop photosynthesizing and the coral loses its food and color. Coral are actually still alive for three to four weeks after they bleach. If their zooxanthellae return, the coral will survive; otherwise, they die.

Coral also suffer when local homes dump pollution—chemicals like phosphates and nitrogen from detergent or fertilizers—in streams, which encourages the rapid growth of algae. An algae bloom can devastate, rather than help, an already struggling coral colony. Outcompeting coral for space and sunlight, the algae grows over the coral, which also leads to bleaching. Additionally, certain kinds of tiny algae can inhibit coral larvae from successfully settling on surfaces such as rock.

Global Stressors

One of scientists’ biggest concerns is global climate change—the Earth’s oceans are warming. Because coral are already living at the upper limit of their temperature tolerance, even a slight increase in temperature can induce stress and cause them to bleach. “With global warming on the rise, ocean temperatures are increasing and adversely affecting coral reefs,” says Hagedorn.

Another problem is acidification. When increased amounts of carbon dioxide in the atmosphere dissolve in seawater and cause a decrease in the ocean’s pH, this inhibits the corals’ ability to form a calcium carbonate skeleton. Other calcium-dependent sea life—such as clams, oysters, and scallops—are affected by this, too.

Trouble in Paradise

Coral are disappearing around the world, but reefs in the Caribbean are showing the greatest distress. Elkhorn coral, the Caribbean’s primary reef-builder, has declined by about 90 percent since the mid-’80s. Elkhorn and staghorn coral are the first two corals labeled threatened under the Endangered Species Act. That’s why National Zoo scientists like Hagedorn and animal keepers like Henley traveled to Rincon with SECORE to help protect elkhorn coral.

Today, SECORE is made up of scientists and aquarists from around the globe, including the National Zoo. Along with studying coral breeding techniques, the group is training individuals from public aquariums and research institutions from around the world through workshops and on-site instruction.

“SECORE scientists first traveled to Puerto Rico in 2006 to collect coral gametes,” says Hagedorn. “From those efforts, the first elkhorn coral were raised in captivity and are now found in some zoos and aquariums.” Of all places in the Caribbean, Puerto Rico made the most sense for SECORE’s first efforts because it is a well-developed U.S. territory and has the infrastructure that the crew needed. Most importantly, it is home to one of the largest breeding populations of elkhorn coral.

Spawning in Puerto Rico

In an incredible show of nature’s precision, elkhorn coral spawn for just one hour at night once a year. From 9 to 10 p.m., three or four days after the full moon in August, a spawning blizzard occurs just off the shore in Rincon. Elkhorn coral are hermaphrodites—meaning they carry the sex organs of both genders and release small bundles of eggs and sperm. For the past few years, SECORE divers including Henley and Hagedorn havegathered these coral gametes as they disperse. With large butterfly nets in hand, they dive down to the spawning site and catch as many of the floating bundles as they can. Then they transfer the gametes to bottles and pass

scuba diving in Caribbean
National Zoo invertebrate keeper Mike Henley nurtures elkhorn coral gametes through every stage of development (Jay Reynolds/Moody Gardens)

them up to kayaks that bring them to a mini-marine station on the beach. Once there, scientists place them in a large cooler, gently separate the egg-sperm bundles, and stir them for two hours to allow the eggs to fertilize. A fertilized coral egg will become a larva, which later can grow into coral polyps.

In collaboration with Henley and other aquarists, Hagedorn designed the minimarine beach station to provide the best possible care for the coral larvae. Her setup includes a number of small pools—kids’ wading pools filled with seawater from the reef. To keep the pools filled with fresh water, they use more than 75 feet of specially designed PVC piping that can bend around the coral and bring water from the ocean in and out of the pools. For the larvae to flourish, the water must stay fresh and at a constant temperature. The larvae also need to be in motion, so some of the pools have specially designed features that automatically stir it. Because a few of the pools do not have this feature, they must be stirred manually, requiring the group to divide shifts during the day and night.

At the National Zoo

From another Puerto Rico diving excursion in 2007, Hagedorn and Henley brought back 12,000 coral larvae to the National Zoo. Of these, 152 settled onto specially designed tiles and formed what are called polyps—millimeter-sized “baby” corals—that grow and multiply into the clusters that we recognize as coral. In the ocean, reefs that are hundreds of miles wide began with a single polyp. Out of the thousands of larvae from the 2007 trip, only one polyp survived for longer—it was on display at the Invertebrate Exhibit until it died in June.

Why didn’t more coral from the 2007 group survive? “Coral is very difficult to raise in captivity,” says Hagedorn. “For the first three months, it is very sensitive to change— especially to variations in light, pH, and oxygen levels. Overall, however, algae and water quality are the biggest issues.”

alpacas
Elkhorn coral polyps form clusters. (Mehgan Murphy/NZP)

Aquarium enthusiasts know that coral can be easily grown in captivity from broken fragments of parent colonies. But those new coral are clones with the same genetic makeup as the parent coral. They are not genetically diverse, and are therefore less likely to survive environmental changes.

In 2008, SECORE scientists collected and harvested close to one million larvae in Rincon. More than 400,000 were brought back to zoos and aquariums, and now around 3,000 larval recruits are living and thriving at these organizations.

From the 2008 trip, Hagedorn and Henley brought back 36,000 coral larvae to the Zoo. Although 3,500 of these larvae settled, none remain. Other zoos trying to raise the elkhorn coral recruits seem to be experiencing the same problem. Some were able to raise between one to five coral larvae, but not many more than that. One zoo, however, has been hugely successful rearing the larvae. Omaha’s Henry Doorly Zoo is rearing 1,000 coral from the 2007 trip and another 1,000 from 2008. The National Zoo is closely studying Omaha’s techniques to try to reproduce similar successes.

“I really believe in this project,” says Henley. “We need to keep collecting more coral gametes and bringing more larvae back. In case the unthinkable happens and coral go extinct, these zoo populations could be all that’s left.”

Back in the Wild

Should coral disappear, the future thinking programs of SECORE and the National Zoo’s Coral Conservation Program could help reintroduce the animals back into the wild. High-tech solutions such as frozen banks (see “The Deep Freeze”) may provide a major new strategy for zoos and aquariums, enabling them to maintain more live coral in each location.

“We’d love to help reintroduce coral back into the wild someday if the need arises,” says Hagedorn. “But there is still so much we don’t know, like when we should return young coral to their natural habitat. Should they go back when they’re two months old or two years? Much more research needs to happen before we reach that point.”

—Dan Stone is the contributing editor of Smithsonian Zoogoer.

 

More: "The Deep Freeze"

More: "Mighty Microscopic"

 

 


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ZooGoer 38(4) 2009. Copyright 2009 Friends of the National Zoo.
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