Coral Reef Conservation: How Experts Are Boosting Reproduction
Published on October 02, 2013
To us, a coral reef is one of the great beauties in nature. From the coral's point of view, it's a different story.
"Corals are highly aggressive toward each other. People swim on a coral reef and think it's a beautiful, tranquil place," says Mark Schick, collection manager at the Shedd Aquarium in Chicago. "It is a war zone constantly, 24 hours a day."
How can you be aggressive when you're stuck to one place your whole life? "Basically you can grow real fast, or real mean and slow," Schick says.
One technique is to grab as much of the best real estate as possible. "The most valuable property on the reef is sunlight," he says. "Some grow fast and try to shade the neighbor out."
But there are more violent tactics as well. Some corals form a long tentacle with stinging cells called nematocysts on the end. "They're cells that fire like tiny harpoons when they're touched," he says.
There's also chemical warfare — substances thrown out into the water, or more personally delivered. "They can take their stomach and stick it out anywhere on their body," he says. "There's some pretty nasty stuff in there, strong acidic conditions, and they're laying it on their neighbor."
Corals may be good at fighting each other, but there's another battle they can't fight alone. With the SECORE Foundation, Schick works on the conservation of the elkhorn coral. "It was the main reef-building coral in the Caribbean up until about 30 years ago," he says. "Now it's 95 percent to 97 percent gone."
While there are a lot of theories about the decline, scientists aren't sure what's causing it. What is certain is that the fewer corals there are, the harder it is for them to reproduce. This might be true of any animal, but particularly one that is stuck in one place for life.
So scientists are working on breeding them in captivity for reintroduction to the wild — but it's quite different from the process for more familiar animals.
Coral Basics
To start, yes, corals are animals. "Animals at some point in their life have to be able to move on their own, and they cannot create their own food source," Schick says.
Corals fit the first part of the definition because they start out as larvae that swim around for a couple of days before settling down permanently and growing their hard exoskeletons.
As for the second part, they do sort of grow their own food. They have a symbiotic relationship with an algae that lives inside their body, and they absorb the excess nutrients it produces. But it's not really part of them.
In fact, when stressed, the coral may eject all the algae — that's when you get what's called "bleaching" of a coral reef. A bleached coral may die of starvation, but it's not inevitable. "It's kind of one foot in the grave, but they can still come back from it," Schick says.
Making More Coral
Corals have an unusual array of reproduction tactics — some more like plants than animals. For instance, if a piece breaks off and falls to a good spot, it can reattach and grow a new, genetically identical coral. "It's like if you could break a finger off and plant it in the ground, and another 'you' grows out of it," Schick says.
But there are also various types of sexual reproduction. In the species Schick works with, each coral is both male and female, but it can't fertilize itself. Since they can't move to find each other, they throw their sperm and eggs out into the ocean currents to mix together — and they only get one chance per year. "It's usually three to five nights after the full moon in August," he says.
When the fertilized eggs hatch into larvae, they spend three or four days floating around till they find a place to settle down — and they choose very carefully.
"They can sense pressure; if they go too deep, they won't get sunlight. They can sense light, although they don't have eyes," he says.
They also have a tiny mouth that they use to investigate the real estate. "They touch the ground and kind of taste to see what's there, and you can see they have preferences for certain areas to settle," he says.
Recent experiments show that the larvae even have a preference for certain sounds, although they don't have ears. It may be another way to know if they're in the right place, since the open ocean is much quieter than a populated reef.
Coral Matchmakers
Now that the corals are more sparsely distributed, they may throw their eggs and sperm out into the currents and not find any other to mix with. So SECORE workers go out and find corals that are ready to release their sperm and eggs and put a mesh bag over them that has a collecting cup on top.
"When we get back, we gently shake it up like the current to break the sperm and eggs apart," he says. Then they combine the sperm and eggs of different colonies.
Once the larvae hatch, they're given tiles that have been out in the ocean for a while to settle on. Later the tiles are moved out to the reef, where they need to be affixed to the bottom with epoxy — not the sort of equipment you usually think of when you think "wildlife reintroduction."
So why go to all that trouble? It's not just because they are beautiful — coral is important for other species, including our own. "It's a huge habitat for fish in the shallows," Schick says. Fish like to hide, and spawn, in the nooks and crannies, so the more coral, the more fish.
And a coral reef is basically a free breakwater — and one that doesn't have to be rebuilt, because it grows back on its own. "It's great for protecting the island from storms because it breaks up a lot of energy on the reef," Schick says. "If I had a condo on the beach, I'd want a reef in front of it."
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