Biology Of Coral Reef Ecosystems Worksheet Page 3
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4Bio Factsheet
197 Biology of coral reef ecosystems
Typical Exam Question
Fig.2 shows the decline in coral cover on the Great Barrier Reef.
Fig.3 shows the number of reefs on the Great Barrier Reef damaged by episodes of coral bleaching. Bleaching results when changed
abiotic conditions cause the coral polyps to expel algae or when the algae lose chlorophyll. The coral then becomes totally white.
Fig.2 Decline of coral cover
Fig.3 Coral bleaching
6 0
500
5 0
400
4 0
300
3 0
200
2 0
100
1 0
1960
1970
1980
1990
2000
0
1960
1970
1980
1990
2000
Year
Year
Each point = mean cover of up to 241 reefs sampled in each year
(a) Suggest two abiotic factors that could influence coral bleaching. (2)
(b) Explain why bleaching may lead to the death of the coral reef
(2)
(c) Fig.4 shows the number of reefs on the Great Barrier Reef damaged by outbreaks of crown-of-thorns starfish (COTS). Fig.5 shows
part of the food web of the reef.
Fig 4 Outbreaks of crown-of-thorns
Fig 5 Coral reef food web
Octopus
Giant clam
500
Crown of Thorns Starfish
Crabs
400
Sea urchins
300
Sea stars
Coral
200
Sea slugs
100
Sponges
Zooplankton
0
1970
1960
1980
1990
2000
Year
Phytoplankton
Explain how overfishing may have contributed to the decline of the reef (3)
Markscheme
(a) temperature;
salinity;
sedimentation;
heavy metals;
(b) loss of photosynthesis/key producer;
reduced food supply/oxygen;
(c) Removal of predators of e.g. COTS;
Results in population explosion;
Increasing predation of reef;
3
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