IB Biology SL 4.3.7 Ocean Warming and Coral Reefs

Practise explaining coral bleaching, warming tolerance and ocean-carbonate changes that threaten coral reefs.

Exam points

Explain coral bleaching through loss of zooxanthellae photosynthesis.
Link warming and dissolved carbon dioxide to coral growth and reef survival.

[Maximum number: 2]

High-temperature tolerance experiments were performed on Pocillopora damicornis, a coral in the tropical eastern Pacific, in the Gulf of Panama. The scattergraph shows the zooxanthellae densities at three temperature treatments over a 10-week period.

Figure for Question D4.3.7—Coral reef threats question 1 — IB Biology SL

Using the data, explain the effect of temperature on coral bleaching in the Gulf of Panama.

a. bleaching is zooxanthellae expulsion from coral;

b. high temperature/ $30^{\circ} \mathrm{C} / 32^{\circ} \mathrm{C}$ resulted in loss/death of zooxanthellae (causing bleaching)

OR

negative correlation between temperature and zooxanthellae density OR

positive correlation between temperature and bleaching;

c. photosynthesis in zooxanthellae disrupted which leads to expulsion of zooxanthellae

OR

production of toxic substances which leads to expulsion of zooxanthellae;

2 max

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D4.3.7—Coral reef threats question 1