Especially after the Industrial Revolution, the amount of Carbon Dioxide (CO2) in the atmosphere is constantly on a rise. And with the constant annihilation of forests, the trees and other vegetations can't keep up with the accretion of carbon dioxide. So Carbon Dioxide became the ultimate culprit of Ocean Acidification. 30% of the Carbon Dioxide in the atmosphere diffuses into the ocean. The Carbon Dioxide creates bond with the water molecule (H2O) to create carbonic acid (H2CO3), a weak acid. Though carbonic acid is not a strong acid, but in the same way, it releases H+ ions into the its surrounding, successfully increasing the acidity of the ocean. So far, ocean pH has dropped from 8.2 to 8.1 since the industrial revolution, and is expected by fall another 0.3 to 0.4 pH units by the end of the century.
Importance
Why does the decrease in pH matter? Well, in humans, for example, normal blood pH ranges between 7.35 and 7.45. The drop in blood pH of 0.2-0.3 can cause seizures, comas, and even death. Similarly, a small change in the pH of seawater can have harmful effects on marine life, impacting chemical communication, reproduction, and growth.
In addition, the decrease in pH also means the presence of more H+ ions in the water. These hydrogen ions bond with is carbonate (CO3-2), a key component of calcium carbonate (CaCO3) shells. So instead, a bicarbonate ion (HCO3-) is formed. Shell-building organisms can't extract the carbonate ion they need from bicarbonate, preventing them from using that carbonate to grow new shell. Even if animals are able to build skeletons in more acidic water, they may have to spend more energy to do so, taking away resources from other activities like reproduction.
Reef-building corals, similarly, craft their own homes from calcium carbonate, forming complex reefs that house the coral animals themselves and provide habitat for many other organisms. Acidification may limit coral growth by corroding pre-existing coral skeletons while simultaneously slowing the growth of new ones, and the weaker reefs that result will be more vulnerable to erosion.
So as long as the Ocean Acidification continue, the balance of the Oceans will continue to be destroyed. More shell-building animals become susceptible to their predators. More coral reefs will be destroyed and the animals housed in them will be affected too. And more animals will then appear on the endangered species list.