We present experiments that examined the metamorphosis, growth, and survivorship of larvae from three species of commercially and ecologically valuable shellfish (Mercenaria mercenaria, Argopecten irradians, and Crassostrea virginica) at the levels of CO₂ projected to occur during the 21st century and beyond. Under CO₂ concentrations estimated to occur later this century (~66 Pa, 650 ppm), M. mercenaria and A. irradians larvae exhibited dramatic declines (>50%) in survivorship as well as significantly delayed metamorphosis and significantly smaller sizes. Although C. virginica larvae also experienced lowered growth and delayed metamorphosis at ~66 Pa CO₂, their survival was only diminished at ~152 Pa CO₂. The extreme sensitivity of larval stages of shellfish to enhanced levels of CO₂ indicates that current and future increases in pelagic CO₂ concentrations may deplete or alter the composition of shellfish populations in coastal ecosystems.