Friday, May 25, 2018

Coral Reefs, Part I: Plant or Animal?

What makes up only one percent of the ocean but is home to almost one fourth of all marine species?

Coral Reefs

Home to millions of species of fish, crabs, starfish, clams, sponges, squid, lobsters, sea turtles, seahorses, and more, reefs have existed on earth for 400 million years.

Corals may look like rocks or plants, but they are actually animals that have taken 'root' on the ocean floor.  Each coral is like a condo with hundreds of little animals (polyps) living in tiny compartments.

Coral Reef 

What Is A Polyp?

Each coral polyp has a soft jelly-like body living inside a hard outside shell made of calcium carbonate.  As it grows, the animal expands it's home by producing more calcium layers for it's shell.

Coral Polyps

The polyp is a simple animal consisting of feeding tentacles surrounding a mouth that leads down to a digestive system. Food goes in the mouth and waste come out the same way.

Inside each polyp's body lives a small--but important--one-celled algae called zooxanthellae. The zooxanthellae creates oxygen and food for the polyp.  It is the zooxanthellae that gives the coral it's color.

In exchange for providing food and oxygen, the zooxanthellae gets a safe home, creating a symbiotic relationship where both parties benefit.

What Do Reefs Need To Survive?

Corals can live for thousands of years, and some reefs can grow as big as a car.  In order for a reef to survive, there must be:
  • clean salt water
  • sunlight
  • a smooth substrate
  • herbivorous fish*
  • food**
*The herbivorous fish have a very important job.  They eat unwanted algae that grows on the outside of the polyp's shell, preventing it from smothering the polyp.

**The zooxanthellae produces enough food to keep the polyp alive, but it needs additional food, like plankton, in order to thrive and grow.  

Why Are Reefs Important?

Reefs are important for many reasons:
Coral reefs are extremely important to our earth and to our human existence.  But, alas, our reefs are in deep trouble.   

Coral Stress Bleaching

Please stay tuned for Coral Reefs, Part II to learn ways to help our reefs before it is too late.  If we care for the reefs, they will care for us.       

Research Sources:

1.  "Corals".  NOAA National Ocean Service Education.  National Oceanic and Atmospheric Administration.  Web.  14 May 2018.  <>.

2.  "Shallow Coral Reef Habitat".  National Oceanic and Atmospheric Administration: NOAA.  Web.  15 Apr. 2018.  <>. 

Image Credits:

1.  Reef and Clownfish by Miriamichelle is licensed under CCO Creative Commons.

2.  Coral Polyps and Fish by marcelokato is licensed under CCO Creative Commons.

3.  Coral Polyps by Dr. Robert Ricker.  Image ID: rikr005l.  NOAA'S Coral Kingdom Collection.  National Oceanic Atmospheric Administration/Department of Commerce.

4.  Coral Reefs/Coral Stress Bleaching by David Burdick.  Image ID: reef3076.  NOAA'S Coral Kingdom Collection.  National Oceanic Atmospheric Administration/Department of Commerce. 

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