Low oxygen waters are also acidified waters, but studies investigating how these two conditions affect marine life together have been lacking. The combined effects of low oxygen and low pH led to higher rates of death and slower growth than by either individual factor. Further, in some cases there was negative synergy between these environmental factors, which means that the performance of the animals was worse than predicted by either individual factor. Hypoxia and acidification have additive and synergistic negative effects on the growth, survival, and metamorphosis of early life stage bivalves. Low oxygen zones in coastal and open ocean ecosystems have expanded in recent decades, a trend that will accelerate with climatic warming. There is growing recognition that low oxygen regions of the ocean are also acidified, a condition that will intensify with rising levels of atmospheric CO2 due to the burning of fossil fuels causing ocean acidification. Hence, the low oxygen, low pH conditions used in this study will be increasingly common in the World's Oceans in the future.