Question

coral reefs are ideal breeding grounds for a variety of fish and sea creatures, and coral is considered a foundation species. unfortunately, coral reefs are fragile ecosystems and are easily disrupted. because coral contain calcium carbonate deposits, one situation poses a growing threat to coral as well as the many organisms that are dependent on them. that situation is
a the disappearance of certain species of fish due to overfishing.
b the deposition of calcium on the reefs, due to the leaching of calcium from dead organisms.
c over exposure to sunlight due to the relatively shallow nature of the ocean around the reefs.
d acidification of the ocean caused by increased atmospheric carbon dioxide emissions that dissolve in water.

Explanation:

Ocean acidification from dissolved atmospheric CO₂ reacts with calcium carbonate (the main component of coral skeletons), breaking it down and hindering coral growth. This directly targets the calcium carbonate structure mentioned in the question, making it the key threat to coral reefs among the options. Other options do not directly impact the coral's calcium carbonate deposits as described.

Answer:

D. acidification of the ocean caused by increased atmospheric carbon dioxide emissions that dissolve in water.