ANEMONES AND CORALS: Anthozoa

PHYSICAL CHARACTERISTICS

Anemones (uh-NEH-muh-nees) and corals are polyps (PAH-luhps), which are tubular sacs with a mouth and tentacles on a flattened upper surface called the oral disk. Most of these animals have stingers in their tentacles. The mouth and tentacles face up, and the base of the polyp is attached to the material on which the animal lives. The mouth opening leads into a digestive cavity. Hairlike fibers lining the digestive tract funnel water into the body. Anemones and corals live alone or in colonies. Solitary animals are commonly 0.5 to 2 inches (1.3 to 5 centimeters) in diameter at the oral disk, but the largest species grows to 3 feet (1 meter) across. The polyps of colonial species are typically smaller than those of anemones and corals that live alone, but the colonies themselves can be quite large. Anemones and corals look like flowers, bushes, feathers, fans, and even a brain.

Many species of anemones and corals make skeletons. In some of these species the living tissue lies above an outer skeleton made of calcium carbonate secreted by the outer layer of tissue. It is these skeletons that form the framework of tropical coral reefs. Other species secrete a flexible black inner skeleton that has thorns on its surface. Still other species secrete an inner skeleton made of calcium carbonate, a protein called gorgonin, or a combination of the two. Soft corals lack a supporting inner skeleton and can inflate or deflate by funneling water into or out of themselves.

GEOGRAPHIC RANGE

Anemones and corals live in oceans all over the world.

HABITAT

Anemones and corals live in the sea in areas that are exposed at low tide all the way to the deepest ocean. Solitary forms may be attached to a hard material or may burrow into soft bottom mud or sand. Colonies build a crust on hard surfaces or build massive skeletons. Reef-building corals usually live in clear, shallow, warm water, although a few species live in the cold, dark, deep sea.

DIET

Most anemones and corals eat plankton, or microscopic plants and animals drifting in water. Drifting prey are captured when they come in contact with the extended tentacles. Prey capture also may involve the firing of stingers. Many corals make slimy mucus that traps floating and sinking food particles. Large sea anemones may feed on crabs, clams and mussels, and fish. Many anemones and corals also receive nutrition from algae (AL-jee) living inside them. Algae are plantlike growths that live in water and have no true roots, stems, or leaves.

BEHAVIOR AND REPRODUCTION

Anemones and corals aggressively defend their space from neighboring animals of the same and different species. The tentacles used for defense are modified feeding tentacles. Some corals develop sweeper tentacles after prolonged contact with foreign species. These tentacles are five to ten times longer than feeding tentacles and have more stingers. The sweeper tentacles search an area around the coral polyp and cause tissue death in neighboring species on contact. Similar structures in sea anemones are called catch tentacles.

Several species of anemones and corals produce light when an intruder makes contact with the colony. This light may be a bright green flash from a tube or a wave of light across the colony as polyps flash in sequence from the point of contact. The light probably is used to startle predators.

Anemones and corals use asexual (ay-SEK-shuh-wuhl)or sexual reproduction. Sexual reproduction takes place with, and asexual reproduction takes place without, the uniting of egg and sperm and the transfer of DNA from two parents. For asexual reproduction anemone and coral polyps split either lengthwise or crosswise and form two new individuals. In many sea anemones pieces of the base tear off or break free and develop into new individuals. After a free-living larva (LAR-vuh) settles, it transforms into a polyp that repeatedly divides to give rise to additional polyps, all of which remain connected by living tissue. A larva is an animal in an early stage that changes form before becoming an adult. In some species, buds may be released from the polyps of the parent colony, and these then settle and develop a new colony. For many hard corals, damage caused by storms or strong wave action produces fragments that grow into new colonies.

Depending on the species, anemones and corals have separate sexes or have both sexes in the same animal. Anemones and corals lack well-defined sex organs. Rather, the eggs and sperm accumulate in a layer of tissue. The eggs and sperm are shed into the body cavity and are either released through the mouth for fertilization (FUR-teh-lih-zay-shun), the joining of egg and sperm to start development, outside the body, or stay inside the animal for fertilization inside the body with release of the embryos through the mouth at a later time. Embryos of anemones and corals develop into larvae (LAR-vee) that may or may not feed and that can stay in open water for days to weeks.

One of the most spectacular behaviors of anemones and corals is the simultaneous release of sperm and eggs by many colonies over a wide area of coral reef. During these mass spawning events, huge slicks of eggs and sperm and developing larvae can be seen on the water surface, attracting a variety of predators that feed on the spawned eggs.

CORAL REEFS

Coral polyps excrete, or discharge, a calcium carbonate shell around their bodies. As the animals die, the shells harden, and new polyps grow over them. After many years of this process, coral reefs form. Coral reefs are important to the environment because they support thousands of species of animals and plants and they protect the shore from the ocean. During the tsunami of December 2004 in the Indian Ocean, communities that were protected by coral reefs suffered much less damage than other communities. Human activities such as fishing, hotel construction, and pollution have damaged coral reefs.

ANEMONES, CORALS, AND PEOPLE

Coral reefs are a major tourist destination and source of recreation. Corals provide a habitat for a variety of animals that humans use for food, such as fish, clams, and crabs. Anemones and corals are sold for home aquariums, and coral skeletons are used to make jewelry. Coral skeletons are used as building material and in bone grafts, because the structure of the coral skeleton is similar to that of human bone. Some corals produce compounds that have been harvested to make drugs for treating cancer.

ANEMONES AND CLOWNFISH

Clownfish live with giant sea anemones in coral reefs. The anemone eats prey it paralyzes with poisonous stingers discharged from its tentacles. Clownfish are immune to the stingers and can nestle among the tentacles without harm. The bright colors and markings of the clownfish attract larger fish to the anemone. If they come too close, the larger fish are stung by the tentacles and eaten by the anemone. The clownfish shares in the meal.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists two species of anemones and corals as Vulnerable, or facing high risk of extinction in the wild.

GIANT GREEN ANEMONE (Anthopleura xanthogrammica): SPECIES ACCOUNTS

Physical characteristics: Giant green anemones have a large, flat oral disk almost 10 inches (25 centimeters) in diameter. The body column is densely covered with hollow, sticky, wartlike bumps. The tentacles and disk are emerald green. The column is olive or brownish.

Geographic range: Giant green anemones live off the western coast of North America from Alaska to Baja California.

Habitat: Giant green anemones live in areas exposed at low tide where they are subject to strong wave action.

Diet: Giant green anemones feed on sea urchins, crabs, and mussels. These anemones benefit when urchins fleeing from predatory sea stars fall into their tentacles. They also obtain nutrients from algae that live in them.

Behavior and reproduction: Scientists do not know how giant green anemones behave. These animals have separate sexes and can reproduce when they are five to ten years old. The larvae eat algae. These anemones do not use asexual reproduction.

Giant green anemones and people: Giant green anemones produce toxins that stimulate human heart muscle and have been considered for medical use.

Conservation status: Giant green anemones are not threatened or endangered. ∎

FRILLED ANEMONE (Metridium senile): SPECIES ACCOUNTS

Physical characteristics: Frilled anemones have hundreds to thousands of small, slender tentacles on a lobed crown, giving them a feathery appearance. They are about 12 inches (30 centimeters) tall. The body column is smooth with a distinct collar below the tentacles. The color varies from white to brownish orange.

Geographic range: Frilled anemones live in the Arctic region, and their range extends south to New Jersey, United States, in the western part of the Atlantic Ocean; Spain in the eastern part of the Atlantic; southern California, United States, in the eastern part of the Pacific Ocean; and South Korea in the western part of the Pacific.

Habitat: Frilled anemones attach themselves to rocks, shells, wood, and other hard materials in areas exposed at low tide to water as deep as 540 feet (165 meters).

Diet: Frilled anemones trap prey in mucus-coated tentacles. Prey include tiny crustaceans and the larvae of mollusks. Crustaceans (krus-TAY-shuns) are water-dwelling animals that have jointed legs and a hard shell but no backbone. Mollusks (MAH-lusks) are animals with a soft, unsegmented body that may or may not have a shell.

Behavior and reproduction: Frilled anemones adjust the length of their body column to the flow of the current. They use catch tentacles equipped with stingers to attack other species in competition for their space. The tips of the catch tentacles remain attached to the victim. Frilled anemones have separate sexes. The males release sperm into the water, and fertilization takes place inside the female's body. These anemones reproduce asexually by splitting in two or when a piece of the base breaks off and grows into a new individual.

Frilled anemones and people: Frilled anemones have no known importance to people.

Conservation status: Frilled anemones are not threatened or endangered. ∎

RED CORAL (Corallium rubrum): SPECIES ACCOUNTS

Physical characteristics: Red coral forms tree-shaped colonies. This coral has a red calcium carbonate skeleton almost 20 inches (50 centimeters) tall. Tiny hard rods are embedded in the outer part of the animal's body. Feeding tubes with eight tentacles can be completely withdrawn into the animal's tissue. Red coral also has tiny nonfeeding tubes that lack tentacles and contain the sex organs.

Geographic range: Red coral lives in the central and western parts of the Mediterranean Sea and in the Atlantic Ocean off the coast of southern Portugal and northern Africa.

Habitat: Red coral lives on cave walls, vertical cliffs, and overhangs in water 33 to 820 feet (10 to 250 meters) deep.

Diet: Red coral uses its tentacles to capture animal plankton. It also may directly absorb dissolved nutrients from the water through its outer layer of tissue.

Behavior and reproduction: Scientists do not know how red coral behaves. This coral has separate sexes. Male colonies release sperm that swim and are carried by currents to female colonies. Eggs are fertilized inside the females and develop inside for about thirty days. Nonfeeding larvae are released and swim for as long as fifteen days before settling. Red coral sometimes but rarely reproduces asexually.

Red coral and people: The skeleton of red coral is highly valued for jewelry. The ancient Phoenicians, Egyptians, and Romans used coral for trade. According to Greek legend, red coral confers magical powers such as defending ships against lightning and eliminating hatred from the home. Powdered coral skeleton is sold as an herbal medicine to treat digestive and other disorders.

Conservation status: Red coral is not threatened or endangered. ∎

DEEP WATER REEF CORAL (Lophelia pertusa): SPECIES ACCOUNTS

Physical characteristics: Deep water reef coral is white or pink and forms irregularly branched bushy or treelike colonies up to 6 feet, 6 inches (2 meters) tall. The brittle tubular branches are about three-eighths to five-eighths inch (1 to 1.5 centimeters) thick.

Geographic range: Deep water reef coral lives in the Atlantic Ocean, the northwestern part of the Pacific Ocean, the Indian Ocean, and in the waters south of New Zealand.

Habitat: Deep water reef coral lives in cold, deep water on hard material. Colonies combine to build reefs and mounds as large as 660 feet (200 meters) high, 0.6 mile (1 kilometer) wide, and 3 miles (5 kilometers) long.

Diet: Deep water reef coral feeds on animal plankton.

Behavior and reproduction: Scientists do not know how deep water reef coral behaves or whether it uses sexual reproduction. Asexual reproduction of new colonies occurs when the fragile branches break and fragments continue to grow.

Deep water reef coral and people: Deep water reef coral has no known importance to people.

Conservation status: Deep water reef coral is not threatened or endangered. ∎

BLACK CORAL (Antipathella fiordensis): SPECIES ACCOUNTS

Physical characteristics: Black coral grows in densely branched treelike colonies that reach a height of more than 16 feet (5 meters). The tiny white polyps are arranged in rows. Six tentacles surround a raised mouth. The skeleton is made of a black protein and is covered with spines.

Geographic range: Black coral lives only in waters near southwestern New Zealand.

Habitat: Black coral attaches itself to the walls of narrow inlets from the sea that are 13 to 328 feet (4 to 100 meters) deep.

Diet: Black coral eats animal plankton, which it captures by direct contact with its tentacles.

Behavior and reproduction: Black coral has sweeper tentacles that are up to eight times longer and more densely covered with stingers than other tentacles. The coral uses these tentacles in aggressive competition for space. Black coral has separate sexes. The male releases sperm into the water. After development inside the female, the larvae are born freely swimming.

Black coral and people: The skeleton of black coral is used to make jewelry.

Conservation status: Black coral is not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Carson, Rachel. The Edge of the Sea. 1955. Reprint, Boston: Mariner, 1998.

Cousteau Society. Corals: The Sea's Great Builders. New York: Simon & Schuster, 1992.

Niesen, Thomas M. The Marine Biology Coloring Book. 2nd ed. New York: HarperResource, 2000.

Wells, Sue, and Nick Hanna. The Greenpeace Book of Coral Reefs. New York: Sterling, 1992.

Web sites:

"About Coral and Coral Reefs." Coral Reef Adventure. http://www.coralfilm.com/about.html (accessed on January 24, 2005).

"Conservationists Fear Worst over Tsunami Damage, Urge Lessons to be Learned." Terradaily.http://www.terradaily.com/2005/050109021602.j5xmgg5g.html (accessed on January 31, 2005).

"Corals and Anemones." Sea and Sky. http://www.seasky.org/reeflife/sea2b.html (accessed on January 25, 2005).

"Welcome to Corals." National Oceanic and Atmospheric Administration. http://www.nos.noaa.gov/education/kits/corals/welcome.html (accessed on January 25, 2005).