Scientists are studying coral reefs around the world to discover the impact that warmer temperatures and increased carbon dioxide may have on the life cycle of corals. "Changing Planet" is produced in partnership with the National Science Foundation.
ANNE THOMPSON, reporting:
Just beneath the surface of tropical ocean waters lives a world of stunning beauty and incredible biological diversity unlike anywhere else.
These are coral reefs, part of the oceans infrastructure that play several crucial roles in our environment. Thousands of species of fish and other marine animals depend on the reefs, protective habitats that are the backbone of billion dollar economies built on fishing and tourism. The reefs are also natural storm barriers and help protect against coastal erosion.
But these important natural structures are under siege as warming water temperatures and increasing ocean acidity take their toll.
Dr. ANDREAS ANDERSSON (Bermuda Institute of Ocean Sciences): The effect on corals and other organisms we know from experiments that we have done in the laboratory so we can take corals and put them in a tank and we can manipulate the seawater chemistry.
THOMPSON: Researchers from the Bermuda Institute of Ocean Sciences work in the waters off the island of Bermuda, studying the effects of warmer temperatures and the changes in ocean chemistry, known as ocean acidification, on coral reefs.
ANDERSSON: The temperature and the ocean acidification, they interact so corals may be more vulnerable to warming, for example, when you have ocean acidification. And ocean acidification may be more on the longer-term threats to the corals.
THOMPSON: Corals are temperature-sensitive marine animals made up of hundreds, even thousands of little polyps. Colorful algae, called zooxanthellae, live inside the coral tissue, and as the algae photosynthesize they provide the coral with up to 95 percent of its food.
But even a small increase in water temperature, as little as a couple of degrees, could spell disaster, forcing the colorful algae to leave the coral tissue. The coral then becomes white. This process, called coral bleaching, means the coral will starve and could eventually die.
Dr. SAMANTHA DE PUTRON (Bermuda Institute of Ocean Sciences): From bleaching events that they seen in the Caribbean, reefs have been wiped out. The corals themselves on the reefs have died within a matter of weeks.
THOMPSON: Coral bleaching spans the globe. It devastated reefs in the Indian Ocean in 1998, the Caribbean Sea in 2005, and Australia's Great Barrier Reef in 2002 and 2006.
In 2010 NOAA, the National Oceanic and Atmospheric Administration, reported that temperatures tied for the warmest year on record, a factor in the massive coral bleaching in the Indo-Pacific region known as the "Coral Triangle."
It's not just the ocean's temperature that is rising, the water is absorbing more carbon and that creates a whole other set of problems.
Rebecca Albright is researching the impact of climate change on coral at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.
REBECCA ALBRIGHT (University of Miami): We call-- global warming's lesser-known cousin is ocean acidification. And ocean acidification refers to the decrease in the pH of the oceans.
THOMPSON: About 30-percent of the carbon dioxide, or CO2, that is in the atmosphere is absorbed by the ocean. Here in the salt water it forms carbonic acid. This increases the acidity of the water and decreases the pH and the amount of carbonate ions, the building blocks necessary for corals to build reefs.
ALBRIGHT: Anything in the ocean that lays down a calcium carbonate shell or skeleton in order to protect itself, it makes it much more difficult for those organisms to secrete calcium carbonate as the pH goes down.
THOMPSON: This means corals will grow more slowly and possibly be weaker.
ALBRIGHT: And so you have natural destructive processes such as wave activity that erodes the reef on a daily basis. And if we're not replacing that at the same rate through natural reef accretion then we have a net loss of our reefs overtime.
THOMPSON: Increases in ocean temperature and acidity threaten not just the corals that are in the water today, but these changes could severely impact future generations of coral.
To study the effects of increased carbon dioxide levels on the early stages of the coral life cycle, Albright collects the egg and sperm bundles that are released into the water during the spawning cycle. Back in the lab the eggs are fertilized and kept under various temperatures and acidity levels.
Albright's research shows that lower pH in the water interferes with coral reproduction and all stages of early life.
ALBRIGHT: And so right off the bat, you're limiting the number of individuals you start with because you have fewer eggs that are fertilized. And then fewer of those eggs, actually develop into larvae and settle on to the reef. And fewer of those grow and survive. And so, it's just a successive decline.
THOMPSON: Can we reverse this process?
ALBRIGHT: With global warming and ocean acidification, that is a global problem that needs to be addressed on a global scale. And ultimately, the only solution to those problems is reducing carbon dioxide emissions and turning to more sustainable sources of energy. But I think that understanding how much coral reefs give us in terms of ecological services, just learning the value of them is the first step in saving them.
THOMPSON: Forfeiting these incredible underwater ecosystems would be a great loss to both marine animals and humans around the world.
And saving the reefs will take a worldwide effort if we hope to preserve the beautiful, fragile world under the sea.
Australia's Great Barrier Reef may never recover from last year's warming-driven coral bleaching, said a study that called for urgent action in the face of ineffective conservation efforts.
Record-high temperatures in 2015 and 2016 drove an unprecedented bleaching episode, which occurs when stressed corals expel the algae that live in their tissue and provide them with food.
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