Coral and Coral Reefs


A coral is a structure made from millions of very small sea animals, called polyps. A single tube -shaped polyp is only an inch in length . At one end its mouth is surrounded by tentacles that bring sea animals toward it. Corals are very colorful and grow in many different sizes and shapes . They have a skeleton that is outside or inside its body.

They can be soft, stony , black, thorny and other types. Some look like feathers or fingers. Polyps are hollow and attach themselves to other polyps or limestone rock to form big structures. Almost all corals live together in groups called colonies. Very big colonies are called reefs .
Polyps take calcium from seawater and turn it into limestone around the lower part of their body. New polyps grow and the limestone structure becomes larger and larger.

Corals live in oceans all over the world but can survive best in warm water. In tropical oceans they form large structures called reefs. Atolls grow around old volcanoes and are islands that form a ring

Coral polyps eat small sea animals like the larvae of jellyfish .  Some need algae to survive. Corals can reproduce by budding. Small buds appear on the body of a polyp. They grow larger and separate from their parents. Corals can also produce eggs that grow into new colonies. Some types of corals live on for hundreds of years.


Coral Reef

A coral reef is an underwater mountain formed by the skeletons of corals.  Reefs also contain other animals like algae or shellfish . A coral reef has many bright colors and can grow for hundreds of years without being destroyed by the ocean.



There are types of corals:

  • Fringing reefs  are near the coastline . They are usually the youngest reef forms.
  • Barrier reefs are farther away from the shore. They form a wall between shallow water near the coast and the open sea . Some barrier reefs are very large. The longest is the 2000 km long Great Barrier Reef on the eastern coast of Australia .
  • Atolls are ring-shaped reefs . They form when an old volcano erupts and sinks into the sea. The reef grows up from the edge of the volcanoes with a lagoon forming in the middle.

Most reefs need warm water to survive. They grow best in water that is at least between 16 and 20° C. Reefs also need enough sunlight to make food.

Coral reefs can be found in the warm ocean waters of the Pacific and Indian Ocean as well as the Caribbean Sea and the Eastern coast of central South America. They normally grow very slowly, not more than 10 cm a year. They can be found near the surface where they get enough sunlight.

Life on coral reefs

A coral reef may have thousands of different species of corals and other organisms . Except for tropical rain forests they contain more different organisms than any other ecosystem . They are called the rain forests of the sea.

Many types of fish live near coral reefs. Their bodies have changed in a way that makes it possible for them to live and find food in this area. In addition coral reefs are also homes of crabs , lobsters , octopuses , sea stars and other animals that have no backbones .



Importance of Corals and Coral Reefs

  • Corals remove and recycle carbon dioxide , a gas that is responsible for the greenhouse effect .
  • Reefs protect land from waves and storms, and allow other types of organisms to flourish in the shallow water near the coast
  • Reefs attract millions of tourists every year
  • Jewels are made of coral reefs
  • A coral reef is a complex ecosystem with different kinds of organisms. Without the reef they would die
  • Corel skeletons are used as substitutes for bones and other parts of our body
  • Coral reefs are living laboratories for scientists and students


Major threats to coral reefs

  • The fishing industry has destroyed many coral reefs
  • Cutting down of forests and construction work near coastlines cause soil , mud and sand to be washed into the sea. Thus sunlight is blocked out and cannot get to the reefs
  • Trash dumped into the ocean can also damage coral reefs
  • Fertilizers and human waste are dumped into the ocean. Algae grow quicker and cut off light and oxygen which corals need to survive
  • Careless boating and diving can also lead to the destruction of reefs.
  • Global warming has lead to a rise in ocean temperature. High water temperatures make corals bleach and die.


Downloadable PDF Text- and Worksheets


Related Topics




  • algae = a very simple plant that grows in our near water
  • appear = are seen
  • atoll = a coral island in the shape of a ring
  • attach = fasten, hang on to
  • attract = here: make people come to visit
  • backbone = a row of connected bones that go down the middle of your back
  • bleach = when the colour of something goes away
  • block out = something cannot get in
  • bud = a rolled up leaf before it opens
  • calcium = a silver white metal that helps to form teeth, bones and chalk
  • carbon dioxide = a gas that is produced when people or animals breathe out or when carbon is burned in the air
  • careless = not careful
  • coastline = where the sea meets land
  • contain = hold, have
  • crab = a sea animal with a hard shell , five legs on each side and two large claws
  • destroy = to damage completely
  • destruction =ruin, damage
  • dump = put
  • ecosystem = the animals and plants in an area and the way they live with each other; how they live in their natural surroundings
  • edge = border, outer side of
  • erupt = explode
  • fertilizer = a substance that you put on the soil to make plants grow
  • flourish = grow
  • fringe = to hang down over an object
  • hollow = empty inside
  • in addition = also
  • inch = about 2.54 cm
  • jellyfish = a sea animal that has a round body that you can see through; it can also sting you
  • jewel = a valuable stone, like a diamond; you can make a necklace or bracelet out of it
  • laboratory = a special room in which a scientist does his work or carries out experiments
  • lagoon =a lake of sea water that is separated from the open ocean by rocks, sand or coral
  • larva-larvae = a young insect with a soft tube-shaped body, which will later become an insect
  • length = how long something is
  • limestone =a rock that is made out of calcium
  • lobster = a sea animal with eight legs, a shell and two large claws
  • mud = wet earth that has become soft and sticky
  • octopus = a sea creature with eight long arms
  • organism = a living thing
  • oxygen = a colourless gas that is in the atmosphere and that we need to breathe
  • protect = guard, defend
  • recycle = to use again
  • reef = line of sharp rocks made of corals
  • remove = get rid of, do away with
  • reproduce = to produce young corals
  • responsible = in charge of , to blame
  • rise = to go up, increase
  • scientist = a person who is trained in science and works in a laboratory
  • separate = divide, break apart
  • shallow = not very deep
  • shape = form
  • shellfish = an animal that lives in water and has a shell; it can be eaten as food , like crabs, lobsters and oysters
  • soil = the top layer of the earth in which plants grow
  • species = a group of animals or plants whose members are similar to each other; they can breed and produce young ones
  • stony = made out of stone
  • structure = a built object
  • substitute = alternative, instead of
  • surface = the top layer of something
  • surround = to be around something
  • survive = to live on, especially after a dangerous situation
  • tentacle =a long thin part of a sea animal which it uses for holding things
  • thorny = with sharp points that grow out of it
  • thus = that is why
  • trash = waste; material that we don’t need any more
  • tube = like a round pipe
  • waste = leftovers, trash