Omaha Zoo Has a Coral Whisperer Beside the Tanks

Forgive Mitch Carl if he sounds like a proud papa.

Carl, an aquarium supervisor at the Henry Doorly Zoo, seems to have a knack for growing a rare but important species of coral from larvae.

In 2006, an international team of scientists and aquarium specialists, led by Holland’s Rotterdam Zoo and including Carl, undertook the most ambitious effort ever to establish captive populations of elkhorn coral, using eggs and sperm gathered in the wild.

Of about 500,000 embryos sent to various zoos, only 1,100 survived three months — all in Carl’s care.

Last year’s harvest produced better success rates for researchers at nine sites in the United States, but again Carl’s batch fared the best. Three months after the larvae were brought to zoos, 75 percent of Carl’s had survived. The next closest success rate was about 50 percent.

It’s no mere academic endeavor. The work "probably will be very important" to replenishing the rapidly disappearing coral reefs of the Caribbean, said Mike Brittsan, curator at the Columbus Zoo and Aquarium in Ohio.

Brittsan is U.S. coordinator for the research project, which has been dubbed "SECORE" for Sexual Reproduction of Coral.

About 90 percent of the world’s elkhorn coral has disappeared over the past 20 years, largely because of human activities, Brittsan said.

What the dull-brown elkhorn lacks in beauty it makes up in importance to the web of life under sea and to shoreline stability.

Elkhorn coral, which can grow to the size of a car, spreads broad fans that provide a forested habitat for sea creatures.

When an elkhorn colony dies, its skeleton serves as a structure for other marine life to adhere to and grow. Long networks of elkhorn coral reefs protect shorelines from harsh waves.

What makes sexual reproduction of elkhorn coral important is that it offers the opportunity to more quickly grow larger numbers of more genetically diverse coral specimens. Traditionally, elkhorn coral has been grown in captivity through cloning — breaking off a piece and letting it root, so to speak.

The problem with cloning, Carl said, is that it is slow, offers no genetic diversity and causes successive generations to adapt to the captive environment, thus becoming less suitable for reintroduction to the wild.

The effort to sexually reproduce coral in captivity is the brainchild of coral biologist Dirk Petersen of the Rotterdam Zoo.

Elkhorn coral are animals, but because they are rooted in one place they have developed a simultaneous, group release of eggs and sperm for the best chance of fertilization.

Through what is believed to be a variety of chemical, light and water-movement cues, vast reefs of coral release their sperm and eggs en masse each evening for a couple of days shortly after the full moon in August or September. The timing is so precise that the spawning begins each of those nights at 9:15 p.m. and ends 45 minutes later.

For the past two years, researchers have swum into what sometimes looks like a snowstorm of sperm and eggs, scooping up millions of specimens. From those, hundreds of thousands become embryos, then thousands survive to larval stage and, finally, hundreds grow into coral colonies.

Any number of problems can cause the developing coral to die. A major threat is suffocation from algae that settle on microscopic coral polyps.

Carl breeds and nurtures the coral in the basement of the Henry Doorly Zoo’s aquarium. Flat tanks of crystal clear water ripple with wave action and house the coral, along with their natural caretakers — fish, urchins, snails and hermit crabs that eat algae.

"It’s nice to look down at a tank and see your little babies."

Larvae he nurtured into coral colonies have been shipped to zoos across the United States and in Europe.

It’s hard to say why he has been so successful, he said. Maybe it’s his obsession with keeping the water clean. Maybe it’s the mix of oyster eggs, briny shrimp and other foods he feeds the coral. Maybe it’s the lighting or the wave action.

As part of this project, Carl has shared his practices with his colleagues during training sessions in Puerto Rico and Holland. Other researchers are getting up to speed and the knowledge base now exists, Brittsan said, to move to the next phase: seaside cultivation.

Growing coral in their home environment will be essential to replenishing coral reefs, Brittsan said. It’s not advisable to transfer specimens grown in zoos to the wild because of the risk of introducing a foreign organism into the sea.

Instead, the specimens Carl and others are raising will be used to stock aquariums around the world so that more people have a chance to see what elkhorn coral looks like. Elkhorn coral are officially listed as endangered, so harvesting live specimens from the sea is prohibited.

Even the Henry Doorly Zoo does not have elkhorn coral on public exhibition. This project, though, offers the opportunity to do so one day.

That Carl would prove pivotal in the race to save coral reflects well on his work and on Henry Doorly Zoo’s commitment to science, Brittsan said.

It’s also proof that success in saving this species is growing from a partnership of top research scientists in the field and those laboring in the trenches in zoos across the country.

"If we work together, we can make a difference," Brittsan said.

Carl, 34, got his start as a kid with an aquarium, and he is not too many years removed from his job at a pet store. With a degree in biology from the University of Nebraska at Omaha, he’s been with the zoo for 10 years.

Through his passion as a hobbyist and now as a professional, Carl said, he’s developing a sense of what coral prefer. That’s crucial, because much about coral remains unknown.

"Even the best and the brightest in the field," he said, "don’t know everything about coral, don’t know everything that makes them tick."