Here, two juvenile elkhorn corals only 26 days old have survived a sojourn in the open water but have successfully settled onto a surface to begin their life’s work of building a colony. Future endeavors may not be as successful. Credit: Rebecca Albright/RSMAS, Univ. of Miami

The oceans are changing. You can’t tell by standing on a beach and watching waves roll in, but experiments show that ocean water is becoming more acidic. This process is called “acidification,” and it may mean bad news for animals like the elkhorn coral, which is found throughout the Caribbean Sea.

Elkhorn coral used to be easy to find in shallow water, but now it’s an endangered species. In the last 30 years, many populations of elkhorn coral have collapsed, thanks to disease outbreaks, hurricanes and elevated temperatures. Scientists are working on ways to save the coral, but they have a long way to go. A new study suggests that coral may face yet another threat: In more acidic waters, elkhorn coral are less successful at reproducing sexually.

A substance may be an acid or a base. Acids taste tart and may be corrosive, like vinegar or even battery acid. Bases tend to be slippery. Water is neutral, which means it’s right between acids and bases. Right now, the oceans are slightly more basic than water. But oceans are beginning to move more to the acidic side.

As acidification worsens, these elkhorn coral may produce fewer offspring. This change could mean fewer or smaller coral reefs — which could be a problem for the many animals and plants that live on those reefs.

Acidification happens because oceans absorb a gas called carbon dioxide from the atmosphere, and carbon dioxide makes the water more acidic. Carbon dioxide, or CO₂, in the atmosphere comes from many sources, and human activities have added a significant amount. When we burn oil or gas to generate power (such as electricity or to fuel cars), we add CO₂ to the air.

Carbon dioxide is also a greenhouse gas, which means it traps heat in the air — which leads to warmer temperatures on Earth’s surface. This is called global warming, and CO₂ is one of many gases that drive global warming.

And since the beginning of the industrial revolution more than 200 years ago, the amount of CO₂ in the atmosphere has been increasing quickly. This change in the air has affected the oceans, forcing them to absorb even more carbon dioxide.

Scientists estimate that oceans have become about 30 percent more acidic in the last 200 years. Previous studies have shown that marine animals like corals, oysters and sea urchins have a hard time building their shells and skeletons in more acidic water.

The new study was led by Rebecca Albright, a graduate student at the University of Miami. She wanted to know how elkhorn coral would reproduce in acidic water. To find out, she and her team added bubbles of carbon dioxide to ocean water in a tank to make it more acidic — like it will be in the future. The scientists placed elkhorn coral in the water.

Coral usually grows in reefs, and coral reefs often look like giant, colorful rocks in shallow parts of the ocean. They provide a home to many kinds of plants and animals. But coral is neither a rock nor a plant — it’s an unusual animal. Like other animals, elkhorn coral reproduces sexually, which means a sperm cell and egg cell come together to create a new organism.

Albright and her team observed that for coral living in water with extra carbon dioxide, sperm and egg combined less often than they do in ordinary seawater. Then she observed another obstacle to coral reproduction: Even if a sperm and egg managed to join, they had a hard time getting settled on the reef to grow.

As oceans become more acidic, the elkhorn coral may face increasing problems producing offspring. And it’s just one species.

It’s possible that elkhorn coral could evolve and adapt to the changing climate. “One of the limits with this kind of study is that it doesn’t tell you whether there is any potential for evolutionary changes to deal with the new stress,” Steve Gaines told Science News. He is an ecologist at the University of California, Santa Barbara, and did not work on Albright’s study.

However, Gaines points out, the climate is changing unusually fast. The bottom line remains the same: More carbon dioxide means more acidification, which probably means bad news for the elkhorn coral.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

acid Any of a class of substances whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals to form salts.

evolution The process by which species adapt and change over time.

carbon dioxide A colorless, odorless, incombustible gas formed during respiration, combustion and organic decomposition and used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers and aerosols.

coral Any of numerous, chiefly colonial marine polyps of the class Anthozoa.

The December 2004 Sumatran tsunami battered, but didn’t break, the 1,192 atolls of the Maldives. This image, taken by NASA’s Terra spacecraft, shows some of the atolls.

NASA/GSFC/ASTER Science Team

In December 2004, a large, undersea earthquake rumbled in the Indian Ocean off the coast of Sumatra. The earthquake triggered a tsunami, or a series of large, destructive waves, that traveled across the ocean in all directions (see “Wave of Destruction”).

The Maldives, a nation of about 1,200 islands southwest of India, were in the tsunami’s path. The islands of the Maldives are made up of coral reefs built on top of the craters of a range of undersea volcanoes. The land surface, which is coral and sand, is just above sea level.

The Maldives are a group of coral islands resting on top of an ancient volcanic mountain range off the coast of India.

NASA

The 2004 tsunami was devastating to the people of the Maldives. It flooded many of the islands and left 80 people dead.

Scientists had worried that the tsunami might badly damage the land surface, too, by permanently sweeping away much of the islands’ sand.

But when researchers went back to study the sand depths and new shorelines, they found that the islands themselves had survived. The waves carved away parts of the sandy cliffs and beaches on one side of the islands but put sand back on the opposite coast.

That’s similar to the effect of monsoon winds. The winds blow across the islands in one direction in summer and in the opposite direction in winter, moving sand back and forth between the two coasts. The sand changes places but doesn’t disappear.

The islands’ remoteness may have helped protect them, the researchers say.

The tsunami waves that hit the Maldives were only one-fifth the height of the ones that swept over Thailand. That’s because tsunami waves grow taller as the sea gets shallower, which occurs near a large land mass or a continent. But in the deep ocean around the reef islands, the waves didn’t have time to grow to great heights.—C. Gramling

Going Deeper:

Gramling, Carolyn. 2006. Still standing: Tsunamis won’t wash away Maldives atolls. Science News 169(March 25):181. Available at http://www.sciencenews.org/articles/20060325/fob5.asp .

You can learn more about the Maldives and how wind and waves shape these coral islands at earthobservatory.nasa.gov/Study/Maldives/ (NASA).

Sohn, Emily. 2005. Forests as a tsunami shield. Science News for Kids (Nov. 2). Available at http://www.sciencenewsforkids.org/articles/20051102/Note2.asp .

______. 2005. Wave of destruction. Science News for Kids (Jan. 19). Available at http://www.sciencenewsforkids.org/articles/20050119/Feature1.asp .

______. 2005. Digging into a tsunami disaster. Science News for Kids (Jan. 12). Available at http://www.sciencenewsforkids.org/articles/20050112/Note2.asp .

In this beautiful environment, bright-pink corals tower more than 10 feet tall. Delicate, lacy sponges mingle with brilliant, lemon-yellow sponges the size of boulders. There are shrimp, crabs, sea anemones that look like Venus flytraps, as well as red octopuses, sea stars, fish, and more. All these creatures live between 4,000 and 12,000 feet beneath the surface of the Pacific Ocean.

A Venus flytrap sea anemone on Davidson Seamount.

© 2002 MBARI/NOAA

“It’s an Alice in Wonderland place,” says Dave Clague, a geologist at the Monterey Bay Aquarium Research Institute (MBARI). “I’ve done a lot of dives in the ocean, and I’ve never seen biological communities like this before in the deep sea.”

In January 2006, researchers returned to Davidson Seamount, bringing equipment that enabled them to better explore this intriguing underwater ecosystem. This time, they focused on the area’s large gardens of coral. It’s rare for corals to be so big, bright, and diverse in the cold, dark depths, and the scientists wanted to learn more.

The team included scientists from the National Oceanic and Atmospheric Administration’s (NOAA) Monterey Bay National Marine Sanctuary, MBARI, and Moss Landing Marine Laboratories. A film crew from the British Broadcasting Company (BBC) tagged along, and the team posted dispatches, videos, and photos online during the 10-day expedition (see oceanexplorer.noaa.gov/explorations/06davidson/welcome.html).

Undersea mountain

Located 75 miles southwest of Monterey, Calif., Davidson Seamount is one peak in a long chain of underwater mountains that stretch offshore from Baja, Mexico, to central California, Clague says.

Davidson Seamount is an extinct volcano located about 75 miles (120 kilometers) southwest of Monterey Bay, California.

© 2003 MBARI

The seamount used to be an underwater volcano, but it stopped erupting some 10 million years ago, according to analyses of rocks collected on the first expedition. Today, the seamount is 26 miles long and 7,900 feet high, about as lofty as Mount St. Helens in Washington State.

Scientists made maps of the seamount in the 1930s. But because the area is so deep, exploring it was impossible before the invention of robotic machines called remotely operated vehicles (ROVs). Pilots control ROVs from the sea surface, and the machines carry cameras, mechanical arms, and other equipment.

For the 2006 expedition, the ROV Tiburon joined the team. A group of otters greeted the research ship Western Flyer as it left the bay, and a pack of dolphins and porpoises escorted it along its 6-hour journey.

For the next 10 days, Tiburon explored underwater slopes for 8 to 10 hours a day, says team member Allen Andrews, a marine biologist at Moss Landing Marine Laboratories.

This photo shows three types of sponges growing on the lava of Davidson Seamount: large yellow sponges; white, frilly sponges (left); and white, bushy sponges. The large yellow sponge provides a perch for several basket stars and pink shrimp.

© 2006 MBARI/NOAA

The ROV used its arm to collect samples of rocks, mud, corals, and other animals. It also carried a high-definition video camera that sent images to the surface. Scientists on the ship took turns sitting in the “science chair,” where they watched the spectacular view on a big screen. They saved the recordings of the scenes for later analyses.

“It’s very exciting to get to the bottom and see things that no one has ever seen before,” Andrews says.

Valuable real estate

Seamounts are valuable real estate for deep-sea creatures because they provide rocky surfaces to which the animals can affix themselves. Scientists suspect that currents play an important role, too, by delivering streams of nutrients to fuel the ecosystem.

Equipment placed on the seafloor measures currents flowing over the top of Davidson Seamount.

© 2006 MBARI/NOAA

On the most recent expedition, researchers brought along equipment to measure currents so that they could get a sense of how the seamount’s ridges have become so rich with life.

Mapping the patterns of currents could also help explain why certain types of corals live where they do. For example, on the 2002 expedition, scientists noticed that two types of coral dominated the mountaintop, Clague says.

Most areas were crowded with big pink bubblegum corals, but another section of rock was covered with tiny, thumb-size corals and crusty sponges. As different as the two communities are, one might be overtaking the other, the researchers suggest.

These bubblegum corals grow to more than 8 feet tall on Davidson Seamount. They eat tiny particles that they’ve filtered out of the passing currents. Unlike tropical corals, deep-water corals live in water that is just a few degrees above freezing.

© 2006 MBARI/NOAA

Another goal of the mission was to figure out how long the seamount’s big corals live. Evidence from previous expeditions suggests that some corals might be more than 100 years old. Andrews plans to test the new samples for a type of radioactivity that indicates age.

“There are a lot of neat questions that have never been asked,” Clague says. “We have never seen something so dramatic in the deep sea.”

Unexplored realms

Like the majority of the world’s oceans, much of the Davidson Seamount remains unexplored. Learning more about these special places will be an essential part of keeping them in good shape, Andrews says.

Bamboo corals on Davidson Seamount may live to be more than 200 years old.

© 2006 MBARI/NOAA

That’s important because deep-sea coral communities appear to be very old and very fragile. It would take them a long time to recover from damage, if they recovered at all.

“There are seamounts around the world that used to have very diverse coral communities, and they are completely gone,” Andrews says. “If we don’t protect this place from being damaged by human activities, we will lose something that no one will ever be able to see again.”

Going Deeper:

Additional Information

Questions about the Article

Word Find: Coral Gardens