It takes a bit of travel to see the world's coral reefs. Spectacular specimens can be found in the Caribbean, the Florida Keys or the Christmas Islands in the Indian Ocean. 

But to visit with some of the scientists who study coral, the trip's not nearly as exotic.

Nearly 30 coral reef ecologists are based at Pennsylvania State University in State College, Pa. They study how corals—the animals that build reefs—live and respond to their environment.

Animal, plant or mineral?

Iliana Baums, a Penn State associate professor of biology, is among the scientists concerned about bleaching and the ability for corals to adjust to climate change.

"A lot of people are unsure what corals are. A lot of people think they are rocks for example," Baums said.

"If folks don't know that they are living animals it's harder to talk about what's threatening them and what we need to do to save them," she said.

Imagine a jellyfish turned upside down and connected to a piece of rock. Up close, that's what individual coral polyps kind of look like.

Thousands live together in a colony and form a veneer of tissue—and over time build a hard, calcium carbonate skeleton to create the reef.

"It's just like our bones," Baums said. "It's not a living animal, it's just that top layer of the coral colony that's alive."

"Some of them are about the same size as a head of a pen," said John Parkinson, a molecular biologist and graduate student in the Baums lab.

"Within a surface area of about a couple of centimeters, you find five to 10 polyps."

A strained, intimate partnership

"What's unique about the coral is ... their success is dependent on an association with another species that actually lives inside of them," Parkinson said.

Baums calls it a "tight partnership with single-celled algae."

The algae inside the coral convert sunlight to fuel and then share that fuel with the host coral.

"That extra energy is really useful, it's like candy that helps them get through the rest of the work of actually growing large and strong," Parkinson said. "Without the symbiotic algae, the coral can survive but they are weakened."

The algae are also, mostly, responsible for the amazing colors that corals display.

Parkinson says the partnership between coral and algae is sensitive to slight increases in water temperature. Under stress and high temperatures, the algae produce extra oxygen that is toxic to the corals.

"The algae and the corals disassociate from one another," Parkinson said. 

"And when that partnership breaks down is when the coral show their true color," Baums said.

"Corals become bone white. That's the process of bleaching, and that's what we are trying to understand," Parkinson said.

"Some people take issue with this statement, but a lot of corals are living close to their limit in terms of heat," he said.

Ecosystem engineers

If corals aren't adapting to higher temperatures, the results may be fewer species to build coral reefs. Baums and Parkinson may be be biased by their life's work but make a strong case for coral conservation.

"Coral [reefs] are the trees of the ocean," Baums said. "Fish take shelter in corals, and lobsters live there and octopus and clams and muscles."

The hard structures that corals build are called barrier reefs because they protect coastlines from high waves during storms.

"Ecosystem engineers is what we call them," Baums said.

There's also lots of money made on corals.

"Having pretty coral reefs provides economic incentive," Parkinson said. "So, there's actually billions made in the U.S. alone on coral tourism. They're definitely worth keeping around if we can."

New science underway

In order to figure out how much time corals have left, Baum is working to figure out the age of corals alive today.

The idea, she says, is to learn what conditions coral have lived through to better understand how flexible they can be in the face of climate fluctuations.

Water temperatures are on the rise Baums says—and from a coral's perspective—those temperatures have been "recent and sudden."

"Some of them might actually be capable of living at higher water temperatures, but the problem is this sudden increase. It's like asking you to run an ultra marathon without training at all," she said. "We all have capacity to adjust to our changing environment, but there might be a limit to that."

Coral animals don't show outward signs of aging, so Baums and her team are testing a molecular technique—examining coral DNA—to pinpoint their longevity.

"They don't get gray beards, they don't stoop, they don't have worn out teeth," Baums said.

When cells divide, the genetic information in DNA needs to be duplicated. The machinery that does that duplication is extremely accurate—but occasionally makes mistakes—a mutation occurs.

Baums says there's something like a clock inside coral cells that keeps track as duplication mistakes accumulate.

"We can sort of count," Parkinson explains. "And back track. If this is the rate of mutations and these are the number of mutations that we see, how long has this coral been alive?"

"This is very preliminary data, we're not entirely sure yet, but right now it looks like one of the oldest colonies we work with in the Florida Keys is about 4,000 years old," Parkinson said.

Bristlecone pines and certain fungi are that old, but that kind of longevity is rare.

The 4,000-year-old age estimate is for the coral animals—not for the reefs, not the species in general.

"I thought they might be a couple hundred years old, or maybe three hundred years old on the outside," Baums said. "That's good news to some degree because that means these are true survivors, they've been through a lot."

Baums and her team are still working through the publishing and peer-review process in search of a reliable way to age-date corals.

"Scientists are a conservative bunch for good reason," Baums said. "Sometimes if you come up with a new method—a new way of doing something—it can take a little bit to convince your colleagues that what you are doing is done right."