Question

the population of the coral lophelia pertusa declined significantly around 9,000 years ago in the alboran sea and around 11,000 years ago near the mauritanian coast. using the ratio of manganese to calcium, which inversely correlates with ocean oxygenation levels, marine scientist rodrigo da costa portilho-ramos and colleagues evaluated whether oxygenation played a role in the declines of l. pertusa. the researchers concluded that oxygenation may have been important in the alboran sea but not near the mauritanian coast, since
which choice most effectively uses data from the graph to complete the statement?
a. a substantial increase in oxygenation in the alboran sea corresponded with the local decline in l. pertusa, but the opposite relationship between oxygenation and l. pertusa was found near the mauritanian coast
b. l. pertusa declined in the alboran sea during a period of substantial local decline in oxygenation, but l. pertusa declined near the mauritanian coast during a period of little local change in oxygenation.
c. oxygenation in the alboran sea was higher before the decline in l. pertusa than after the decline, whereas oxygenation near the mauritanian coast was relatively low both before and after the decline in l. pertusa.
d. oxygenation in the alboran sea tended to be substantially higher than oxygenation near the mauritanian coast during the period studied.

Explanation:

• First, recall that the ratio of manganese to calcium inversely correlates with ocean oxygenation levels (higher ratio = lower oxygenation).
• For the Alboran Sea: The coral declined around 9000 years ago. Looking at the graph, around 9000 years ago (x - axis value of 9), the ratio (which is inversely related to oxygenation) shows a significant change (a peak - like behavior). A decrease in the ratio (since ratio $\propto\frac{1}{\text{oxygenation}}$) means an increase in oxygenation. But wait, no - actually, if the ratio (manganese to calcium) is high, oxygenation is low. The coral decline in the Alboran Sea (9000 years ago) corresponds to a significant change in the ratio (a big drop in the ratio, which means a big increase in oxygenation).
• For the Mauritanian coast: The coral declined around 11000 years ago. At 11000 years ago (x - axis value of 11), the ratio (and thus oxygenation) shows little change.

Answer:

B. L. pertusa declined in the Alboran Sea during a period of substantial local decline in oxygenation, but L. pertusa declined near the Mauritanian coast during a period of little local change in oxygenation.