Diving to Rescue Coral Reefs
by Ruth A. Musgrave
Filmmakers Michele and Howard Hall dive into an eerie world. The usually colorful corals are a ghostly white. Most of the fish, crabs, and other animals have disappeared. The reef is sick and dying.
How different this coral reef near Fiji is from the Great Barrier Reef the Halls filmed in Australia. There, in a healthy reef, schools of fish swam through brightly colored corals that decorated the seafloor like flowers in a springtime garden.
Diving for hundreds of hours with bulky camera equipment, fighting dangerous currents, and avoiding sharks, the Halls capture it all. Their IMAX movie will show the world both the beauty and the destruction in the coral reefs.
An Ancient Web of Life
Coral reefs are often called “the rainforests of the sea” because of their abundance of life forms. A great diversity of animals finds food and shelter in every crack and crevice. Some animals eat the coral itself. Others eat the animals that eat the coral. It's a complex food web made up of colorful fishes, eels, octopuses, sponges, shrimps, and crabs. Even sharks, sea turtles, and sea snakes come to the coral reef to find food.
Today's reefs are 5,000 to 10,000 years old. Found in sunny, shallow water in warm seas all over the world, reefs are made up of the hard shells, or exoskeletons, of millions of corals. As corals live and die, their exoskeletons create a giant, rocky honeycomb. Only a thin top layer is living coral.
It takes a long time to make a coral reef. A reef grows only about as fast as your fingernails—three-quarters of an inch a year. But coral reefs are huge, and in time a healthy reef can be thousands of miles long.
“Coral reefs are a story of partnerships,” Michele says. “In the reef, one species needs another to survive.”
One great partnership is between corals and microscopic algae called zooxanthellae (pronounced zo-zan-thell-ee). Together, the algae and the coral build the reef. Zooxanthellae live in the coral's soft tissue, where they are protected and receive the sunlight they need to grow. In turn, the zooxanthellae provide the coral with oxygen and essential nutrients. It is the zooxanthellae that give the corals their rainbow of colors.
The ghostlike corals Michele and Howard found in Fiji had lost their zooxanthellae and turned white. Scientists call this “bleaching.” Unless the zooxanthellae are replaced, the corals will die within a short time.
What's Killing the Coral?
But how zooxanthellae are lost is not completely understood. The Halls and other experts believe that higher sea temperatures may be one explanation. “Unlike the air, ocean temperatures change very slowly,” Michele says. “A change of only one or two degrees can be enough to harm the coral.”
But there may be other causes. “Widespread deforestation is another problem hurting the partnership between corals and zooxanthellae,” Michele explains. How can cutting down trees on land hurt corals in the ocean? When too many trees are removed, the soil is exposed to erosion. Wind and rain wash tons of soil into the sea. A muddy silt then settles on the coral, blocking the sunlight the zooxanthellae need. Other forms of pollution from the land are also harmful. Chemicals from our homes, yards, cars, and factories wash into storm drains and sewage systems. Streams and rivers then carry the chemicals to the ocean.
Destroying the Balance
If the reef is a story of partnerships, then people have a partnership with the reefs, too. Millions of people around the world rely on reef fish and other animals for food. And reefs provide protection from storms at sea. Without thousands of miles of reefs surrounding coastal areas, many beaches and even whole islands could be destroyed by the pounding of powerful ocean waves.
“Reefs save lives in another way, too,” Michele says. Medicines made from compounds found in reefs treat heart disease, leukemia, asthma, and other illnesses. Sometimes people are good partners, protecting and caring for reefs. Sometimes they're not.
In some places, people have taken too many fish and other animals. Often they fish not just for food but for home aquariums or to make jewelry. Sometimes they even use poisons or explosives to catch the fish. These harsh fishing methods kill coral and other animals nearby.
It's easy to destroy the natural balance of the coral reef, according to Michele. “Let's say a grazing animal like the parrot fish is overfished,” she explains. “Without them, the kind of algae that the fish feed on could grow like weeds and take over the reef. The competition for space and sunlight could then starve the coral, making it very hard for the reef to survive.”
Nearly 27 percent of the world's coral reefs have been lost or damaged. But there is hope.
Many reefs around the world—including the Great Barrier Reef in Australia and the reefs off the Florida Keys in the United States—are now protected areas where scientists study how to keep reefs healthy. They determine how many and which kinds of fish can be taken for food without hurting the reef's delicate balance. They also teach reef visitors how to enjoy snorkeling or scuba diving without accidentally harming the habitat that took thousands of years to grow.
The Halls have hope, too, that people will learn to be good partners to the reefs. “We want our film to inspire people to help coral reefs,” says Michele. “For me, as a diver, even though I may not go back to the South Pacific, just knowing the reefs are there and thriving brings a sense of contentment to my spirit.”
Want to learn more about coral reefs?
Read Coral Reefs: Earth's Undersea Treasures by Laurence Pringle.
- Think about the conservation practices that you learned about in Lesson 3. How might recycling paper help to protect coral reefs in the ocean? Write a sentence or two to explain your answer.
- Draw a diagram that shows the path a chemical for killing insects takes from a garden to the ocean. What does the chemical do along the way to the ocean? What does the chemical harm? Label each part of your diagram, including the garden, the water the chemical travels in, and the area where the chemical enters the ocean.