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From above, the ocean looks empty.
Like a desert made of water, it seems barren
... uninhabited.
...But that's just on the surface.
Come below the waves with me as we explore
the riot of color and life that exists on
the coral reefs.
Coral reefs are only found in shallow, tropical
seas.
They may look like colorful rocks, or even
plants, but coral is really an animal. Coral
is built by polyps. Polyps are very small
creatures that are related to jellyfish.
Unlike the jellyfish, which propel themselves around the water, coral are stationary. 
They grow together in a colony called a coral head.
A small piece of coral may be made of hundreds
of polyps. A bigger one may have thousands!
Hard corals create the reef by secreting calcium
carbonate - or limestone, a type of rock,
which gradually builds up into a solid structure.
Coral grows
slowly, only a few centimeters a year. It
can take hundreds of years to form large pieces,
like this.
Of course, not all coral is hard, some types
are soft. They may look like fans, bushes,
or feathers, but once again it is really a
colony of tiny animals living together.
When many corals grow close together, it's
called a reef. Reefs provide very important
habitat for fish and other sea creatures.
Coral provides shelter for little fish - a
place to hide. That many small fish in one
place attracts big fish, which in turn attracts
big predators like sharks.
This nurse shark is unusually active for the
daytime. Usually a nurse shark will hide under
ledges or in crevices of the reef, and come
out at night to eat dormant fish that are hiding in the coral.
Nurse sharks are slow-moving bottom-dwellers,
and, for the most part, harmless to humans
although they can grow up to 14 feet, more
than 4 meters, in length.
Their strong jaws allow them to crush shellfish
and even coral, if need be, but they prefer
to eat shrimp, fish, and squid.
The reef also provides a place for algae and
sponges to grow.
This provides food for a variety of creatures:
for example, the sea turtle.
The Hawksbill Sea turtle, like most other
kinds of sea turtles, is endangered.
Hunted for their meat and for their shells, trapped
in commercial fishing nets to drown, and sickened
by pollution, their populations are
declining.
These turtles rely on the food that grows
on the coral reef - and the reef, in turn,
relies on the turtles.
It's a partnership that benefits both creatures.
The turtles get a reliable source of food.
The reef system gets a less obvious advantage.
Without the turtles coming to eat the algae
and sponges, they would overgrow the reef
- preventing the coral from growing and expanding.
With lowered turtle populations in oceans
worldwide, the health of coral reef systems
will suffer. It is important for people to
do our best to protect these peaceful reptiles,
not just for their sake, but for the health
of the entire coral ecosystem.
Turtles and coral aren't the only partners
you can find on the reef!
Sea anemones are another animal that seems
more like a plant. A relative of both coral
polyps and jellyfish, anemones have their
own partner to help make life easier...clownfish.
Although it may not look like it, Anemones
are predators. They have stinging cells in
their tentacles that allows them to paralyze
their prey - usually small fish, or shrimp
- and then move them towards their mouth.
Clownfish escape the anemone's sting by covering
themselves in a protective layer of mucus!
By hiding inside the anemone, clownfish are
protected from predators that don't want to
be hurt by the anemone.
But what does the anemone get out of this,
you may ask? Well, the little clownfish can
chase away butterfly fish that would eat the
anemone, and they can also clean the anemone
of parasites and bits of food that the anemone
has no way of cleaning itself.
There's one more unusual pairing we're going
to talk about today. Can you guess what parrotfish
and beaches have to do with each other?
Parrotfish are a distinctive family of fish
species with a tough, bony beak so strong
that they can bite through rock and coral! They do
this so that they can eat the coral polyps
and algae inside. The coral is ground up and
all of the
edible parts are digested until only the limestone
remains. Then the parrotfish has to get rid
of all of the crushed limestone - and there's
only one way to do that. The parrotfish will
excrete - or poop out - the limestone, which
has been crushed into a fine sand. 
In this way a single parrotfish can produce 200lb
or 90 kilos of sand every year.
You heard that right. The next time you bury
your toes in soft white sand at the beach,
just remember: you're making castles with
fish poop.
Coral reefs are sometimes called the 'rainforests
of the sea.' Though they cover only a tiny
area of the ocean, they provide a habitat
for a quarter of ocean animals.
Unfortunately, the coral reef ecosystem is
a fragile one. The delicate balance between
the coral, algae, fish, and animals that live
there is easily disrupted.
Overfishing by humans, ocean pollution, and
warming temperatures have all put the world's
coral reefs are at risk. Right now, more than
half of the world's reef systems are in danger
of destruction, and if nothing changes, then
within 15 years nearly all the coral in the
world will be in danger of dying and disappearing.
Fortunately, there are some simple things
you can do to help protect the coral reefs.
Be careful not to waste water, or pour chemicals
down your drain, since eventually the water
you use will reach the ocean and can increase
pollution. Pick up trash that you see on the
ground, and recycle what you can, so that
garbage won't find its way into the water.
Most importantly, make sure people know that
you want to protect the coral reefs, so that
when we make decisions about how to take care
of our world, we will make choices that will
protect the reefs.
I hope you learned something new exploring
the reef with me today! Goodbye till next time!
