| Summary: | Ocean acidification, the consequence of atmospheric CO2 dissolving in the ocean to form carbonic acid, is rapidly intensifying. A wealth of marine wildlife is known to be vulnerable to the expected drop in pH, including a number of crab species. The Dungeness crab (Cancer magister), the target of a commercially important fishery in the Pacific Northwest, is known to be sensitive to elevated CO2 levels. In an effort to better characterize the degree to which C. magister is sensitive to ocean acidification, this study examined the carapace areas, the distance between the eyes, and the molt rates of juveniles reared for over three hundred days in ambient (low) and future (high) CO2 conditions across six instars. Statistical analysis indicates that carapace areas and eye distances were significantly smaller in crabs reared in high-CO2 relative to crabs reared in low-CO2. Effects on carapace area were detectable at the third through the sixth instar, and effects on eye distance were detectable at the second, third, and fifth instar. Molt rates were significantly slower for crabs in high-CO2 treatments for the periods of J1 to J2, J2 to J3, and J3 to J4. If dissolved CO2 levels continue to rise in the ocean, wild juveniles Dungeness crabs may be smaller at each stage and display delays in development. These sensitivities have the potential to affect the crabs’ role in US West Coast food webs and their recruitment into fisheries. Undergraduate
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