As concentrations of CO2 increase in the atmosphere, the ocean absorbs more of it. This is a natural part of the carbon cycle and oceans serve as a vast reservoir for dissolved CO2. The current sea life, especially the phytoplankton and many coral animals have evolved to "like" the current pH of the ocean. As more CO2 is dissolved, it changes the pH and makes the oceans more acidic. If the trend lines continue, acid levels may exceed the ability of many of the micro-organisms at the base of the food chain to cope. This could cause an ecosystem wide crash.