Even corals that have spent generations in acidic waters have failed to adapt completely to these harsh conditions.

As atmospheric levels of carbon dioxide increase, the world's oceans are becoming more acidic, with potentially serious consequences for animals that have carbonate skeletons and shells. Adina Paytan at the University of California, Santa Cruz, and her colleagues collected samples from seven colonies of Porites astreoides coral that live in the seas off the Yucatan Peninsula in southeastern Mexico, where groundwater springs have produced low-pH conditions for thousands of years. These corals had lower growth rates and experienced higher predation by boring organisms than seven samples of the coral living just beyond the influence of springs. Despite living in low-pH areas, these reef-forming organisms will not fully adapt to the ocean acidification conditions expected by 2100, say the authors.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1301589110 (2013)