Coral Reef Formation
Coral reefs are called the forest of
the sea. Why are coral reefs and
forests so important?
• Fish, invertebrates (animals without
backbones), and algae (seaweed) rely on
reefs for food and protection, just as many
plants and animals rely on the forest for
food and protection.
How does a coral reef begin?
Coral reefs form when coral larvae (baby form of a
polyp) settle on a hard substance in warm, clear,
shallow water and begin excreting their skelteons
(taking chemicals out of the water to make their
hard outer skeleton)
It takes millions of coral polyps to make one
colony (group of animals that live and work
together to survive). It takes tens of
thousands to hundreds of thousands of
colonies to make a reef.
How fast do corals produce skeletons?
They only grow a few millimeters a year.
What do corals need to keep growing?
• Sunlight and nutrients (food they take out of
the water that gives them energy to survive
What are the parts of the reef?
1. The inner reef (reef
2. Reef crest (outer edge
of the reef flat
3. Reef face (the leading
edge of the fringing
reef that is always
How is a reef flat formed?
• As the upper tips of coral are exposed to air
too long, they die, leaving a flat surface on
the reef -- a reef flat.
The reef face (also called the fore reef or reef crest) is the
outer ocean edge of a reef. It is where most of the coral
growth occurs. This is one of the most important parts of
the reef to protect.
What happens if corals grow upward
• They will die of exposure during low tides
What is a fringing reef?
• A fringing reef is a reef that is small and
close to an island’s shore.
• This is an early stage in coral reef
Barrier reefs form on an older island. As an
island erodes, the original fringing reef is
located farther and farther offshore, forming a
What is found between a barrier
reef and a volcanic island?
• Usually a lagoon.
What are biological agents of change
on a coral reef?
• All plants and animals that build-up or destroy a reef are
biological agents of change.
What are reef-building agents?
• Organisms that secrete the calcium carbonate
skeletons that form the reef –corals.
• Another important reef building agent are
corraline algae (seaweeds that have calcium
carbonate in their cell walls.)
What are crack-filling agents?
• Organisms that
produce sediments or
that live in the cracks
& crevices of the
• Mollusks, pieces of
• These agents fill in
the areas between
colonies in the reef
What are passive agents?
• Organisms that use the reef to live and hide in, but
that do not affect reef structure.
• They may eat or be eaten by other organisms in the
• Examples: many fish, anemones, crustaceans,
worms, many mollusks, etc.
What are destructive agents?
• Organisms that erode the reef by grinding, chewing,
or boring into it.
• Example: uhu (parrot fish), wana (sea urchins), ka
hoku kai (starfish)
What are physical agents of change?
• Waves, currents, pollution, moving sand, silt
deposits, fresh water, and severe changes in
temperature can affect changes on the reef.
Reef building corals have a symbiotic
relationship with a single celled algae.
The small brown dots in the coral polyps in the picture above
are a single celled algae (zooxanthellae) A symbiotic
relationship is formed when two different species live
together and use each other for survival
What happens when the reef falls
below where sunlight can reach? Why?
• The reef dies because algae cells(xoozanthellae) that
corals depend on for food and oxygen cannot
How is a coral reef like a forest?
Corals are animals that build coral reefs. Reefs
provide a place for seaweed to grow, which provides
food for many other animals. Reefs provide food
and shelter to a variety of sea life. Reefs and forests
are both complete communities of many associated
plants & animals
What are two ways that coral reefs are
of environmental and economical
• Reefs protect coastlines and beaches from erosion
• Reefs form bays and lagoons that provide safety for