What makes up a coral reef ecosystem?
Since coral reefs are found in tropical, shallow waters along migratory paths of birds
and fish, they have all the conditions to create a vibrant, diverse ecosystem. Many people
have described coral reefs as the tropical rainforests of the sea, and judging by the complex
connections between different organisms found in the coral reefs, it seems a fair comparison. Like a
rainforest, coral reefs are very good at cycling nutrients between organisms within the ecosystem and
are very biologically dense, filled to capacity with many different plants and animals.
Coral reefs are characterised by large limestone structures known
as coral. While most people look at these structures and think coral
is completely lifeless, corals are actually created by tiny animals
called polyps.
Coral polyps are tiny animals related to sea anemones and sea
jellies that secrete a limestone skeleton. This skeleton provides a
hard structure that polyps can live on and that protects them from
some predators. They live in communities that are commonly
called coral, which is made up of the limestone skeletons of
previous generations.
Coral polyps live in symbiosis, or in a close, mutually beneficial relationship, with a type of algae
called zooxanthellae. These tiny plants provide food for the polyp, while the polyp provides a
structure for the algae to live on. The algae also use waste products from the polyp, such as carbon
dioxide. Polyps can also receive nourishment by catching other organisms, from plankton and
crustaceans to small fish. They sometimes even attack and digest other types of coral polyps, obtaining
nutrition while they eliminate the competition. Many corals also use chemicals to prevent other corals
from taking hold.
Query??
1.
What is zooxanthallae and why is it important to coral reef ecosystems?
2.
What are coral polyps and what do they feed on?
3.
What is a symbiotic relationship?
4.
Explain the symbiotic relationship between coral polyps and zooxanthellae and describe how
important this is to coral reefs.
Coral provides many things to the other animals living in a coral reef. It can be shelter to small fish, a
hiding place for predators like moray eels, or even food to animals like parrotfish or crown-of-thorns
starfish. The animals that live within and around the coral are also very closely interdependent. The
coral reef food web is very tightly woven. Crustaceans (which are the closest to decomposers in the
coral reef) feed on the detritus (waste products) from plants and animals. These crustaceans are eaten
by molluscs like octopuses as well as small fish. These animals are then in turn eaten by large fish,
who are then eaten by larger fish and sharks. This is only a small example of the enormous food web
that makes up the coral reef ecosystem. In the coral reef, producers include algae and sea plants.
Primary consumers are mostly small fish, molluscs and coral polyps, which are eaten by secondary
consumers like larger fish and sharks.
Animals in the coral reefs have become masters of camouflage. Predators and prey alike have
adaptations that allow them to blend in with the sand, rock, coral and water. Fish have coloured scales
that match their environments. Sharks are coloured in such a way that they blend in with the surface of
the water when viewed from below. Some fish even camouflage themselves as larger organisms by
swimming in schools, or large groups (also called shoals). From far away, some animals might
consider them to be one larger animal. The fish have similar repeating patters such as stripes, making
the blending effect even more deceptive.
Damage to a single part of a coral reef can cause the entire ecosystem to be thrown off balance. If a
population of producers or primary consumers is damaged, secondary consumers will have a hard time
finding things to eat. If an animal that preys on corals polyps is damaged the corals and other similar
animals, like worms and anemones, can overgrow, causing further problems like food shortages and
sediment from detritus. Coral reefs have evolved to be very efficient at regulating themselves and any
damage to them causes this self-regulation to fall off balance
Activity
Imagine you are a diving instructor about to take a group of tourists into the coral
reef environment for the first time. Using pictures and diagrams:a) Describe to them what they can expects to see as they enter the water.
b) Describe how to identify the different types of coral and where to expect to
see the corals on the reef.
c) Explain why the reef will be so colourful.
Handley et al (2007) “Geography Focus Stage Four” Pearson: Sydney p86-7
http://www.skwirk.com.au/p-c_s-57_u-184_t-488_c-1785/what-makes-up-a-coral-reef-ecosystem-/nsw///
http://www.cotf.edu/ete/modules/coralreef/CRatmo.html
http://maxxwi.com/images/0%20coral_reef_4.jpg