Asian Diver – March 2018

What is Coral?

Corals are living animals, and each
coral is an individual animal, or a colony
of identical clones. These animals are
called polyps.
Coral polyps have soft bodies, and are
related to sea anemones and jellyfish.
To protect themselves, coral polyps
build a hard calcium carbonate skeleton
around their soft jelly bodies. If the
polyp is disturbed or in danger, it can
retract into the skeleton. A coral polyp
has a crown of tentacles, a mouth, and
a stomach, and any waste the polyp
produces will exit through its mouth.

Over time, this skeleton builds

up, and different species emerge.

Some corals start to branch,

some make boulders, pillars, or

brains. Some species encrust the

seafloor, while others create tiers of

spiralled plates.

From a tiny individual to a mature

coral colony, no matter the shape or

size, all corals are made of polyps.

To build a reef, coral polyps need

energy which they can get in two ways.

Firstly, at night and sometimes

during the day, polyps will stretch

out their tentacles in hopes of catching

zooplankton or even an unlucky fish.

But staying in one place, trying to

catch food is not a great strategy for

survival. Corals have a secret sidekick

called zooxanthellae. Zooxanthellae

is a photosynthetic marine algae that

lives inside the tissue of a coral polyp.

In exchange for protection within the

polyp, zooxanthellae capture sunlight

and provide energy to the polyp

through photosynthesis.

Coral polyps build

a hard calcium

carbonate skeleton

around their soft

jelly bodies

A coral polyp has a

crown of tentacles,

a mouth, and a

stomach, and any

waste the polyp

produces will exit

through its mouth

Polyps will

stretch out

their tentacles

in hopes of

catching

zooplankton

or even an

unlucky fish

Ca CO

3

Basal Plate

Theca

Septum

Outer Epidermis

Digestive

Filament

Stomach

Gastrodermis

Coenosarc

Mouth

Tentacle

Nematocyst

Mesoglea