IB Biology HL 4.3.7 Ocean Warming and Coral Reefs

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Coral reefs are among the most spectacular ecosystems on Earth. They support a rich diversity of life and provide economic benefits to the people who use them. In Papua New Guinea in the Pacific Ocean north of Australia the following data were collected. Coral cover is the percentage of the reef surface covered by live hard coral.

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

(a)

Acidification of the world's oceans is an increasing threat to the health of oceanic life including coral reefs. Corals perform calcification to create their calcium carbonate exteriors. An experiment was conducted on Heron Island, Southern Great Barrier Reef, Australia. For the experiment the pH was altered by dissolving carbon dioxide in the water. Three different coral species were used, with each test group at two different temperature ranges and three different pH values. The white line in each photograph represents 5 cm .

Porolithon onkodes

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(i)

Describe the trend in calcification when the pH is decreased at $25-26^{\circ} \mathrm{C}$ .

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(ii)

Using all of the data, comment on the hypothesis that ocean acidification in warming seas will have the same effect on all species of coral.

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a. greater reduction in calcification as pH drops at the higher temperature in P. onkodes than on the other two species (so hypothesis not supported)

b. net loss in calcification at lowest pH and highest temperature in P. onkodes whereas there is still calcification in the other two species (so hypothesis not supported)

c. warming reduces calcification at all pH levels in A. intermedia but not in the other two species (so hypothesis not supported)

d. combined effect of acidification and warming is a larger reduction in calcification in A. intermedia than in the other two species (so hypothesis not supported)

e. more calcification as temperature rises at lower pH / pH 7.9 and 7.6 in P. Iobata whereas there is less in the other two species (so hypothesis not supported)

f. more calcification as pH drops from 8.2 to 7.9 at higher temperature in P. Iobata whereas there is a drop/no rise in the other two species (so hypothesis not supported)

This answer is based on the larger drop in calcification between 8.2 and 7.6 at both temperatures in onkodes than the other two species.

This answer is based only on whether there are positive values for calcification or negative.

This answer is based on the drop in calcification at each pH when the temperature rises in intermedia, whereas in the other species there is a rise at one or more of the pHs.

This answer is based on the larger overall drop in calcification between pH 8.2 at $25 / 26^{\circ} \mathrm{C}$ and 7.6 at $28 / 29^{\circ} \mathrm{C}$ .

The answer must either state pHs 7.9 and 7.6 or specify lower pH or greater acidification.

The answer must state the two pH values and state higher temperature or $28-29^{\circ} \mathrm{C}$ .

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(b)

Suggest another marine animal that has parts made of calcium carbonate and may therefore be damaged due to ocean acidification.

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(c)

Outline causes of ocean acidification.

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(d)

Discuss the need for international cooperation to solve the problems of declining coral populations.

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D4.3.7—Coral reef threats question 1

Question (a)

Question (i)

Question (ii)

Question (b)

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Question (d)