Center Guide Book
Marine food chains
The oceanic food chain begins
with microscopic drifting plants called phytoplankton. Phytoplankton are found
close to the surface of the water where there is adequate sunlight for
Phytoplankton are eaten by tiny floating animals known as zooplankton.
Zooplankton include the larvae of crabs, jellyfish, corals and worms, as well as
adult animals like tiny shrimps, copepods and euphausiids. They keep buoyant
with the help of gas-filled chambers and oil droplets which reduce their
Zooplankton in turn are food for fish. Big fish eat smaller fish. At the top of
the food chain are large predatory fish like sharks, mammals like seals, and
seabirds. A very large fish, the whale shark, and some very large mammals, the
baleen whales, feed directly on zooplankton.
Millions of people on all continents depend on fish for food. That is why it is
so important that fish populations are conserved. Overfishing by huge modern
fishing fleets is threatening the entire ocean food chain.
The spectacular coral reefs
Many people mistakenly
believe that coral reefs are made of rock. In fact, coral reefs are made by
millions of tiny animals called coral polyps. They have a soft, sac-like body
with one end closed and the other opening at a mouth surrounded by tentacles
with stinging cells. Each coral polyp secretes a hard limestone skeleton.
Millions of these cases make up the structure of the reef.
Coral reefs are so rich in animal life they have been called the "rainforests of
the sea". A great variety of small colourful fish live around the reef as well
as animals like nudibranchs (sea slugs), sea anemones, sea urchins and starfish.
There are more than 21,000
species of fish, of which most live in the oceans. Scientists classify fish into
two main groups - fishes without jaws (hagfish and lampreys) and fishes with
jaws. The jawed fishes are further divided into those with skeletons made of
cartilage (sharks, chimaeras, skates and rays) and those with bony skeletons
(all the rest, including herring, cod, flounders and barracudas).
Fish have evolved to live in all kinds of marine habitat, from the cold dark
ocean depths to surface waters. Some fish -- the sharks, marlins, swordfish, and
tunas -- are very fast swimmers and efficient predators which move thousands of
km each year. Other kinds of fish such as the flat flounders and plaice move
slowly over the ocean bed where they feed on molluscs and worms. Colourful coral
reef fish tend to stay close to their territory on the reef.
Animals on the ocean floor
The deep ocean floor supports
a special community of animals. Although seaweeds grow from the sea floor near
coasts, it is too dark at the bottom of the deep ocean for plants to live. Some
organisms living here look a little like plants but actually they are animals
like sponges, sea mats, sea anemones, and sea squirts.
Dead plankton, fish and fish faeces fall to the ocean floor where they are
consumed by the decomposers.
Some creatures crawl over the bottom or burrow beneath it. They include
lobsters, crabs, prawns, starfish, brittlestars, featherstars, and many kinds of
sea slugs and worms. Finally, there are the bottom-feeding fish such as rays,
turbots, halibuts and gurnards.
Creatures of the deep
Much of the ocean is so deep that no light penetrates. Many
fish that live at such depths have developed light-emitting organs that signal
other fish or attract prey. The lantern fish has a row of lights long its body
and the angler fish swims around with a lighted rod that attracts other fish,
which are then quickly swallowed!