barnacles attached to a whale.
Photo courtesy Oceania
Crustacean's reproduce in a very similar
way to other animals. The eggs are
produced in the ovaries in the female
and passed to the outside through
oviducts. After the eggs have been
fertilised, they begin development
and then hatch. When the eggs hatch
the young larvae are detached. From
this point on they are on their own
and must grow, swim and survive. After
a series of transformations, the larvae
becomes a miniature adult.
cannot grow as many other animals
do because of their outer skeleton.
Instead they periodically shed the
outer skeleton, grow rapidly for a
short time, and then form another
hard skeleton. While this process
is taking place they hide in an isolated
place. Crustacean are also able to
break off or drop their appendages.
This is called autotomy. They have
special breaking-off points near the
body and if caught they can quickly
break-off their appendages to get
away. A new appendage is easily grown.
Crustacean's food varies, some eat plants,
some eat flesh, and some feed from the
bottom of the ocean on anything they
can find. The way in which they feed
themselves also varies. Barnacles and
anemone crabs use fine hairs on their
appendages to filter food while most
of the larger crustaceans are scavengers.
The cleaner shrimp feeds on the mucus
and parasites covering the skin and
gills of fish.
of crustaceans on the Great Barrier
Plankton is the drifting life of the
oceans. Most planktonic animals are
very small but extremely numerous
and form an extremely important part
of marine food webs. The most common
planktonic animals are the small crustaceans
known as copepods. They are probably
the most numerous animal group in
the world. Together with copepods,
other small crustaceans such as water
fleas combine to make this varied
group a very important part of the
There are about 100 species of barnacle
living on the Reef. Once a barnacle
has found space to live, it stays
put. Pushing its legs out through
a central hole in its cone-shaped
shell, it spends its life lying on
its back kicking food into its mouth.
Barnacles live on hard surfaces including
rocks, boat hulls, jetty piles, and
other crustaceans, and even hitch
rides on turtles and whales.
About fifty per cent of all the mantis
shrimps, krill and crabs in Australia
are found on the Great Barrier Reef.
There are at least 1030 species. Shrimps
are among the most diverse and active
animals on the Reef, performing a
wide range of different roles. Shrimps,
along with crabs, crayfish and prawns,
are characterised by having five pairs
of walking legs, with the first pair
modified to form pincers.
shrimp (Odontodactylus scyllarus)
Mantis shrimps are voracious predators,
feeding on other crustaceans and small
fish - they are also known as 'prawn
killers'. They have formidable claws
that come in two forms: clubs or spears.
Their claws are permanently 'cocked'
back, ready to shoot forward at passing
prey. Those mantis shrimps that possess
clubs use them to smash the legs off
other crustaceans and to crack their
shells open. They can also smash snail
and clam shells to feed on the soft
tissue inside. Those with spear-like
claws use them to strike and kill
fish and other animals. Mantis shrimps
can strike their prey at the speed
of a 0.22 calibre bullet. They are
difficult to keep in captivity because
they can smash aquarium glass up to
two centimetres thick.
This group of crustaceans has
a confusing number of names, including
crayfish, cray, lobster, rock
lobster and spiny lobster. Generally
speaking, the name crayfish is
used to describe those large marine
crustaceans without claws. Lobsters,
on the other hand, have extremely
large and well-developed claws
which can inflict a painful wound
to careless humans. The most commonly
encountered species on the Great
Barrier Reef are the Painted Crayfish
(Panulirus versilcolor) and the
Ornate Crayfish (Panulirus ornatus),
both of which are brightly coloured.
A pair of long slender antennae
extending from under a coral ledge
is generally the first indicator
of the presence of crayfish.
Crabs come in many shapes, sizes
and colours and have tentacles
to feel their way around. Crabs
live in their shells, under
the water and on land. A crab
will shed its shell when it
is too small and will then grow
a new and bigger one. Some crabs
will use another animal's shell
as its home while its shell
is growing. Crabs are scavengers,
feeding on things that are dead
or decaying. They will eat almost
crabs have a body that is too
fragile to survive
use of another marine animals
As they grow they will
have to seek a new shell.
is one from our southern waters.