What are corals?

Welcome to an underwater world!

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Welcome to an underwater world.
Source: NOAA.

When corals are mentioned, most people immediately think about clear, warm tropical seas, shallow lagoons, beaches of sparkling white sand lined with coconut palms.

In fact, the stony shallow-water corals - the kind that builds reefs - are only one type of coral. There are also soft corals and deep water corals that live in dark cold waters.

In this tutorial, however, we will only deal with the shallow depth tropical corals.

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Cup coral
Orange cup coral (Tubastraea faulkneri) open at night to feed in East Timor (Indonesia).
Photo: Wikimedia.

Zoo-what !?!

  • What are coral reefs?
    1. plants
    2. animals
    3. rocks
  • Answer
  • Corals cannot survive without certain organisms. Which?
    1. fishes, octopuses, squids, scallops
    2. worms, shrimps, crabs, lobsters
    3. algae
  • Answer
  • How do corals protect themselves?
    1. they make a limestone cup to hide in
    2. a tiny poisonous layer that covers the coral
    3. tentacles release stinging cells when something brushes by them
  • Answer

What does a polyp look like?

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coral polyp
Cross section of a coral polyp. Source: NOAA

Each individual polyp has a stomach that opens at only one end. This opening, called the mouth, is surrounded by a circle of tentacles. The polyp uses these tentacles for defense, to capture small animals for food, and to clear away debris. Food enters the stomach through the mouth. After the food is consumed, waste products are expelled through the same opening.

Source: NOAA, 2008