What are corals?
Corals are many of the strange underwater shapes that we see in different sizes in warm, tropical seas. Some corals look like human brains. Some corals look like boulders or the horns of an elk or a deer. Corals are what coral reefs are made of. Corals are made of the joined skeletons of tiny underwater animals called coral polyps. (POL-ups).
There are over 2,500 species of corals. About half of these corals (about 1,000) are the hard corals that build coral reefs. Other corals are soft corals. Soft corals have skeletons that are flexible and can bend with the water.
In the Caribbean Sea there are about 60 different species of hard and soft corals.
What are coral polyps?
Coral polyps are animals without backbones (invertebrates). Most coral polyps are smaller than a pea. A coral polyps tiny saclike body is a basically a stomach with arms. Coral polyps look like tiny sea anemones. Coral polyps are related to sea anemones and jellyfishes. These animals all belong to the group of animals in the phylum Cnidaria (Nigh-DARE-ee-uh). Cnidarians are animals that use stinging cells to protect themselves and to catch their food. Most corals polyps form a hard skeleton, outside their bodes, made of limestone (calcium carbonate). The skeleton is in the form of a cup that the polyp lives in. Coral polyp skeletons are joined together to form colonies. Hard corals can make shapes that look like huge brains, elk horns, lettuce leaves, or pillars. Soft corals have skeletons that are flexible and make shapes that look like fans, small trees, vases, or long soft fingers or rods.
What does a coral polyp look like?
The body of a coral polyp looks like a tiny tube closed on one end. Inside the tube is the stomach. The closed end of the tube is called the base. The base is attached to a hard surface and the open end is the mouth with little tentacles that circle the mouth like a crown. Coral polyp colors can include red, orange, yellow, green, blue, purple, and white.
What senses does a coral polyp have?
A coral polyp has no eyes, ears, nose or tongue. A coral polyp also does not have a brain. In place of a brain the polyp has a nerve net. The nerve net goes from the mouth to the tentacles. The tentacles react to touch using tiny sensors on the tentacles stinging cells (nematocysts NEW- mat-o-sists). Similar to our sense of smell, a polyp can detect certain chemicals or substances in the water.
What does a coral polyp eat?
A coral polyp eats tiny animals that drift by called zooplankton (zo-PLANK-tun). Some corals eat little fishes. Most hard corals get some of their nutrition from plant cells under their skin called zooxanthellae (zo-ZAN-thel-lay).
How does a coral polyp eat?
Most coral polyps catch their food at night. At night their tentacles reach out to catch food floating by using the nematocysts in their tentacles. The neumatocysts sting and paralyze the prey and the tentacles bring the food to the mouth. Some corals have long strands of mucus they use like flypaper to catch food that drifts onto it. During the day most hard coral polyps get their nutrition from the zooxanthellae (plant cells) under their skin.
How does a coral polyp reproduce?
When coral polyps are first born they are produced by tiny fertilized eggs. The eggs can be fertilized inside a parent coral polyp or outside the parent after the egg has been released from the parent to drift away in the sea. After eggs are released into water they develop into free-swimming larvae. These larvae settle to the bottom in a few hours and if the conditions are right they will grow into polyps. After coral polyps have established themselves and are healthy they will reproduce by budding. Budding is when a part of the parent polyps splits off and becomes a new polyp. Budding is how coral colonies grow larger. The first polyp splits and makes two, two split and make four, four make eight, eight make sixteen, and so on.
What are the six things most corals need to survive and grow?
2. Salt water.
3. Warm water. (Reef building corals need water temperatures 68ºF-82ºF, 20ºC-28ºC.)
4. Clear, clean water. (Dirty water can block sunlight. Sediments can also choke corals so they cant feed.)
5. Shallow water less than 150 feet (46 meters) deep. (Sunlight is absorbed the deeper you go under the water.)
6. A hard surface.
What is a coral reef
A coral reef is a collection of different kinds of hard corals. The skeletons of hard coral polyps form the limestone (calcium carbonate) structure of the reef. The coral reef we see today may have taken hundreds or thousands of years to grow. The largest coral reef and the largest living organism on planet earth is the Australia Great Barrier Reef. In addition to coral reefs made of living organisms, coral reefs are also homes for many different kinds of plants and animals. Coral reefs are some of the most diverse ecosystems on earth.
What are the three main types of coral reefs?
1. Fringing Reef: These reefs grow near the shorelines. Fringing reefs are the youngest type of reefs. Fringing reefs are the most common reef in the Caribbean Sea.
2. Barrier Reef: These reefs grow parallel to a coastline, far from shore, separated by a wide, deep lagoon.
3. Atoll: Atolls start as fringing reefs around volcanic islands. When the island sinks the reef continues to grow and the coral ring remains where the island used to be. Atolls are the oldest type of reef. Atolls are rare in the Caribbean Sea, but common in the Indo-Pacific.
Where are coral reefs found?
Coral reefs are found in the tropical and subtropical oceans and seas around the world. These warm water areas are between 30ºN and 30ºS latitudes.
How are coral reefs beneficial to people?
- Protect shorelines from damage by waves and storms.
- Provide the sand that makes the beaches in tropical areas.
- Important source of food, including fishes, mollusks, and crustaceans.
- Attract tourists who visit the reefs.
- Remove and recycle carbon dioxide. (Carbon dioxide in excessive amounts can contribute to global warming.)
- Sources for commercial products.
- Coral skeletons used as artificial human bone replacements.
- Sources for anti-cancer drugs and other medicines.
- Living laboratories for scientists to study.
- Support a diverse ecosystem.
How long can coral reefs live?
The coral colonies that make up the reef may live for tens or hundreds of years.
What can damage or kill coral reefs?
- Animals: Animals that eat coral polyps include parrotfishes, butterflyfishes, and sea stars.
- Natural disasters: Natural disasters can include volcanoes, hurricanes, cyclones, abnormal weather, heavy rains, drop or rise in sea level, drop or rise in water temperature, drop or rise in water salinity, drop or rise in nutrient levels, predator population explosions, and coral diseases.
- Humans causes:
- Coastal dredging and development. Can destroy and smother corals.
- Coral mining for use in construction.
- Warm water outflow from power plants.
- Untreated sewage and fertilizer runoff. Added nutrients increase algae growth that can smother corals.
- Deforestation. Topsoil washes down rivers onto corals and smothers them.
- Careless fishing techniques using nets, lines and fish traps. Can damage corals.
- Destructive fishing methods that use dynamite, bleach, or cyanide. Damage or poison corals.
- Collecting corals for use in aquariums, jewelry, and decoration.
- Ocean pollution (garbage, oil spills, poisons, pesticides, radioactive wastes, and other pollutants). Poisons corals.
- Nuclear testing.
- Boats that drop anchors on corals or run into corals.
- People that walk on corals.
- Scuba divers and snorkelers that bump into, sit on, stand on, or grab corals.