Pteropods are snail-like plankton that float through ocean waters consuming smaller plankton. They, like many other marine organisms, rely on the process of calcification to grow their shells (which consist of aragonite and calcium carbonate). Thus, the saturation of carbonate ions in the water is vital to their survival. The increased amount of carbon dioxide in ocean water has shifted the chemical equilibrium such that there is a decreasing concentration of carbonate ions. Studies have shown that pteropods tend to have a slower rate of calcification when placed in water with a high concentration of carbon dioxide. To make matters worse, the decrease in carbonate ions also pushes the saturation horizon closer to the surface of the ocean, reducing the amount of water that pteropods are able to inhabit (calcium carbonite and aragonite will dissolve if placed below the saturation horizon). In addition to problems with building shells, pteropods face a few other potential roadblocks due to ocean acidification. First, they might have to adjust to a new diet; phytoplankton, pteropods’ main food source, will also be negatively affected by ocean acidification, and therefore pteropods could potentially have to deal with either a lack of phytoplankton or a change in what types of phytoplankton they are limited to consuming. Second, they, like many other marine organisms, will have to work harder to regulate bodily processes. The changes in pH of ocean water make it more difficult for pteropods to maintain the proper internal pH; acclimating to the new environment requires energy (which could be put towards other important processes). The combination of all of these roadblocks puts pteropods at risk.