(Describer) Title: Ocean Today.

(female narrator) The many species of ocean coral come in astonishing shapes, colors, and sizes. Some corals are soft, but the ones that build reefs are collectively called hard or stony corals. They have names that match their shapes-- names like staghorn, elkhorn, table coral, and even brain coral. A reef is made when many corals all grow next to and on top of each other over many, many years. This structure is filled with sand and cemented hard.

(Describer) Some corals look like foliage and another is a mound with bumps on it.

We call them corals, but really, each one is a coral colony made up of many quite incredible coral organisms called polyps.

(Describer) C. Mark Eakin:

Corals are amazing organisms. If you think of the game 20 Questions-- "animal, vegetable, or mineral?"-- Corals are all three.

(narrator) Corals are related to jellyfish,

(Describer) Animal.

but they only float in the open as tiny larvae. They then anchor themselves to rocks and hard ocean floors by building a skeleton out of calcium carbonate, or limestone.

(Describer) Mineral.

These stone skeletons, incredibly, are what make up the structure of the reef.

(Describer) In an animation, polyps grow like flowers.

Polyps look a little bit like jellyfish turned upside-down. At night, they send out tentacles to catch little bits of drifting food. This is not how coral polyps get most of their energy. That comes from an amazing partnership between the coral and several types of algae called zooxanthellae.

(Describer) Vegetable.

Zooxanthellae live inside some of the coral's cells. Like plants, they convert the sun's light into food that gives the coral the energy to grow, reproduce, and build its stony skeleton. They also give corals their beautiful colors. The body of a coral polyp is actually almost transparent. When a coral has a healthy amount of zooxanthellae, it's red, gold, or many colors. But when a coral gets stressed, mainly due to high temperatures, the coral expels the algae. Without the algae, the coral bleaches. It loses its color, and more importantly, its main source of food. It becomes weak and more vulnerable to things like disease.

(Describer) Some corals look like white sticks.

If the water cools, corals can recover, but too long without the algae, and they'll die. All over the world, corals are dying more and more often. What's happening and why? Let's look for answers.

(Describer) Divers swim over bleached coral. Titles: Narrator: Lori Berman. OceanToday.noaa.gov. Ocean Today has been brought to you by the Smithsonian Institute in collaboration with the National Oceanic and Atmospheric Administration. Accessibility provided by the US Department of Education.

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Accessibility provided by the U.S. Department of Education.