Biology Of Coral Reef Ecosystems Worksheet printable pdf download

B io F actsheet

Number 197

Biology of coral reef ecosystems

This Factsheet:

Typical Exam Question

•

Describes the structure and functioning of coral reefs

Suggest why the relationship between coral and the

•

Explains why their conservation is considered vital

xooxanthellae can be considered symbiotic.

•

Reviews the kind of exam questions you can expect on this

Answer

synoptic aspect

The algae carry put photosynthesis producing sugars and

oxygen which the coral can use. The algae also assist the coral

Coral reefs are one of the most diverse, productive and complex

in calcification

communities on Earth. Found mainly in shallow, clear, and warm

tropical marine oceans, coral reefs are the largest and most

In return the algae have a relatively safe place to live and are

spectacular structures made by living organisms; reefs such as the

provided with a source of carbon dioxide from coral respiration

Great Barrier Reef in Australia can be seen from space.

The dominant species in a reef ecosystem is the hard (stony) coral,

Table 1 summarises the benefits of symbiosis.

which secretes the exoskeleton of calcium carbonate (CaCO

)

Table 1. Coral and zooxanthellae algae –mutual benefits

However, there are over one million species of organism associated

with coral reefs, thus food chains and webs are complex. However,

Benefits of coral to algae

Benefits of algae to coral

all of this complexity is dependent upon the primary producers:

Allows sunlight to reach

Provides nutrients to coral

•

reef building corals (which contain photosynthetic

algae for photosynthesis

zooxanthellae algae)

Protects algae from harsh

Speeds up coral growth

•

microscopic cyano-bacteria (blue-green algae) which fix nitrogen

environment

and photosynthesise

•

(multicellular) seaweeds

Provide CO

from

Removes waste products from coral

•

phytoplankton floating in the waters around the reef.

respiration for algal

photosynthesis

Fig 1. Coral reef food web

Reef forming coral is not found at depths below 50 metres as the

photosynthetic algae require sunlight. Photosynthesis also

demands a water temperature range of 21-29

C, whilst water clarity,

salinity and water movement need to remain within narrow limits.

Colonies of zooxanthellae live endosymbiotically within the tissues

of other coral reef organisms such as soft coral, as well as

invertebrates such as giant clams, jellyfish, seasquirts, sponges,

flatworms and sea slugs.

Coral Reef structure and function

A coral reef is being continuously formed in two stages: -

(a) Growth of the framework of the reef and

(b) Erosion and cementation.

(a) Growth of the framework

The reef substrate is mainly composed of the calcium carbonate

from living and dead polyps. Millions of polyps grow on top of the

limestone remains of former colonies to create massive reefs. Single-

celled calcareous algae called Foraminifera also add calcareous

compounds to the reef when they decompose.

(b) Cementation

The reef structure can be physically eroded by wave action and

biologically broken down by grazing animals such as parrot fish,

sea urchins and sponges. Small fragments of coral settle into the

Reef-building corals have evolved a symbiotic relationship with a

small spaces in the reef structure. Further cement is supplied by

type of unicellular brown algae called zooxanthellae. Millions of

algae and the nitrogenous excretory products of fish.

these live within the tissues of the polyps.

Biology Of Coral Reef Ecosystems Worksheet

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