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Did you know?
The activity of the zooxanthellae also assists in the release of lime for the
construction of a coral skeleton.
The biggest threat to corals, apart from humans who collect them and pollute the
sea, is coral bleaching.
Coral bleaching
Coral reefs have recently been affected by bleaching i.e. the discoloration or loss of its symbiotic
algae.
The cause of these widespread bleaching incidents is uncertain but recent research indicates that
the cause may be unusually warm waters. The optimum temperature for coral growth is between
26°C and 27°C. Temperatures above 29°C cause the stressed coral polyps to actively expel the
algae giving the coral a bleached appearance.
Bleached corals have difficulty recovering; a reef can take years to recover, and subsequent
bleaching incidents may make it impossible. Without their symbiotic algae, corals are unable to
deposit the calcium carbonate skeleton that makes up the foundation of a coral reef. Not only
corals, but also all reef organisms could potentially lose their habitat because of bleaching
incidents, as the calcium carbonate structure of the reef erodes away.
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
JELLYFISH
Habitat
Ocean
found
the open
often wash
drifters
mainly in
ocean, but
ashore.
Description
Jellies have rounded bell-shaped bodies (medusae), which contain a layer of jelly that consists of
approximately 95% water. This layer varies in thickness in different jellies. They have tentacles at
the open end of the bell that is armed with stinging cells. There is a square mouth with oral arms
called the manubrium.
Feeding
They feed on small fish, shrimps and plankton e.g. fish
larvae.
Predators
They have very few predators of their stinging tentacles.
However, they are an important source of food for some
species of turtle and the ocean sunfish.
Plastic bags drifting in the ocean are often mistaken for
jellyfish by these animals resulting in them eating it by
mistake.
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Did you know?
Some species are considered a delicacy in Japan.
That the box jellyfish can give a painful sting and
that it’s Australian relative can kill a human being
in 3 minutes.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
17
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HYDROIDS
Polyps 2mm to hydroid colonies of 25cm
Habitat
Many of the tufts growing on rocks are hydroids and not seaweeds at all. Some hydroids are
found growing on shells of snails. The hydroids protect the snail by deterring predators while the
hydroids eat the scraps or waste products from the snail. This relationship is commensalism as
the one organism benefits while the other organism is not harmed.
Description
Hydroids form colonies, which often look like delicate trees or feathers. Other species of hydroids
are branched in an orderly and elegant fashion. The tiny polyps are borne on the branches and
may be housed in small cups. The polyps can extend for feeding and can retract into the cups
after feeding. Some hydroids have an external sheath or perisarc made of chitin and protein.
Divers avoid hydroids as they have a fairly powerful sting.
Feeding
Hydroids are carnivorous and use their
tentacles to catch minute shrimps, crabs,
fish and eggs floating in the water. The
digestive enzymes of hydroids are able to
handle large prey.
Predators
Predators are nudibranchs (sea slugs), flat
worms and butterfly fish.
Did you know?
Hydroids are named after Hydra, the multiheaded goddess of Greek mythology
because they multiply by budding.
The Goddess grew two heads in place of
every one Hercules cut off.
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
BLUEBOTTLES
Habitat
Bluebottles live on the surface of the open ocean, but are often blown ashore by onshore winds.
Description
They are unusual hydroid colonies, which consist of
highly specialised individuals that are all
interdependent.
Feeding
They prey on small fishes that they catch with their
tentacles.
Predators
Marine turtles and sea swallows prey on bluebottles.
Plough snails and sea slugs (nudibranchs) may eat
bluebottles washed ashore.
Structure of the bluebottle or
Portuguese man-o’-war
Living Shores: Figure 186
The smaller raft hydroid with a circular raft and
the by-the-wind sailor with an oval raft and
vertical sail are smaller colonies similar to the
bluebottle. They set sail to the wind as a colony,
producing a thin bright blue membrane of stiff
material, orientated diagonally across the colony’s
body.
Did you know?
The painful stings of a bluebottle
should be washed off with salt
water and are best treated with sap
from the leaf of a sour fig plant or
vinegar. A medical practitioner
using antihistamines should treat
severe cases.
Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES
19
Quick review
1.
Identify the animals shown in the table below by giving the Phylum and the common
name.
Phylum:
Phylum:
________________________
Common name:
______________________
Common name:
2.
List three characteristics that all Cnidarians have in common.
3. Label the following parts on the animal below.
b
a
4. Name one interesting thing you would share with a visitor at the touch pool
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Two Oceans Aquarium Volunteer Manual – Module 3 – INVERTEBRATES