Final answer:
Ocean acidification poses the biggest risk to coral reef ecosystems due to its effects on calcium carbonate production in corals.
Explanation:
Ocean acidification is the primary risk to ecosystems of coral reefs. The increased carbon dioxide in the atmosphere leads to increased carbon dioxide in the oceans, making them more acidic. This acidity inhibits the production of calcium carbonate, essential for coral reef structures and organisms.
Learn more about Ocean acidification and coral reefs here:
https://brainly.com/question/23737461
