Ocean acidification harms marine species in various ecosystems. It harms many marine species that rely on carbonate-based shells and those with high sensitivity to acid. Acidification also affects the complex food webs in the ocean. For instance, other marine species high on the food web feed on the ones with high sensitivity. 

Calcifying organisms are marine animals that use calcium carbonate to build their shells and skeletons. These marine species include coral reefs, plankton, oysters, etc. Ocean acidification breaks existing shells and skeletons and makes creating a new one challenging because of the ocean's limited calcium carbonate. 

Their shells become weak and vulnerable to damage from external factors, which weakens their recovery rates. For example, sea urchins help protect coral reefs from algae. However, they can't in acidic coastal areas because their weak protective shells make them more vulnerable to predators.

It also disrupts the food web because calcifying organisms prey on other animals. Some fish species are vulnerable to ocean acidification. Fish eggs and larvae might find it challenging to grow, develop, and survive in acidic oceans. An example is the clownfish larvae, which showed a reduced sense of smell in acidic marine environments, leading to risky swimming behaviors.