Coral reef

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Coral reef
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What is Coral?

• Coral reefs are warm, clear, shallow ocean
  habitats that are rich in life.
• The reef's massive structure is formed from tiny
  spineless animals called coral polyps.
• A polyp has a sac-like body and an opening or
  mouth encircled by stinging tentacles called
  cnidae.
• They secrete a hard calcium carbonate skeleton,
  which serves as a uniform base or substrate for
  the colony.
• This limestone skeleton protects the soft,
  delicate body of the polyp.
• Corals are classified into "hard coral" or "soft
  coral".

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Soft-Coral
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Hard-Coral
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How do corals feed?

• The polyps stretch out their long, stinging
  tentacles to capture the zooplankton that are
  floating by.
• The captured plankton are then put into the
  polyps' mouths and digested in their stomachs.
• In addition, corals rely on the photosynthetic
  products of algae for their food.
• Inside coral tissue lives a one-celled alga
  called zooxanthellae.
• Nutrients from the algae feed the corals,
  allowing them to grow and reproduce.

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How do corals reproduce?

• Corals can reproduce both sexually and asexually.
  
• Some species such as brain and star corals are
  hermaphrodites, meaning they produce both sperm
  and eggs at the same time.
• Other corals, such as Elkhorn and boulder corals,
  are gonophores, meaning that they produce
  single-sex colonies.
• In these species, all of the polyps in one colony
  produce only sperm and all of the polyps in
  another colony produce only eggs.
• Coral polyps spawn on a few nights each year.

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Coral spawning
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Where are coral reefs?

• Coral reefs are found in over 100 countries. Most
  reefs are located between the tropics of Cancer
  and Capricorn, in places such as the Pacific
  Ocean, the Indian Ocean, the Caribbean, the Red
  Sea and the Arabian Gulf.
• Coral reefs grow best in waters with a
  temperature of between 21 and 29 degrees Celsius
  (70 and 85 degrees Fahrenheit).
• Corals need saltwater to survive and require a
  certain balance in the ratio of salt to water.
  This is why corals don't live in areas where
  rivers drain fresh water into the ocean.

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Distribution of coral reefs around the world
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Why are coral reefs so important?

• Coral reefs provide shelter for nearly one
  quarter of all known marine species.
• Also reefs serve as a buffer, protecting inshore
  areas from the pounding of ocean waves.
• Amazingly, more than half of all new cancer drug
  research focuses on marine organisms. The
  beautiful and fragile creatures of our coral
  reefs have the potential to make even greater
  contributions to our lives by providing new cures
  for life-threatening diseases.
• Eg. AZT, a treatment for people with HIV
  infections, which is based on chemicals extracted
  from a Caribbean reef sponge.

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Additional data
Predators Corals are eaten by the
crown-of-thorns (a large starfish that eats coral
polyps), parrotfish, and other animals.
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White death