Ocean acidification, a decrease in the pH in marine waters associated with rising atmospheric CO2 levels, is a serious threat to marine ecosystems. In this paper, we determine the effects of long-term exposure to near-future levels of ocean acidification on the growth, condition, calcification, and survival of juvenile red king crabs, Paralithodes camtschaticus, and Tanner crabs, Chionoecetes bairdi. Juveniles were reared in individual containers for nearly 200 days in flowing control (pH 8.0), pH 7.8, and pH 7.5 seawater at ambient temperatures (range 4.4–11.9 °C). In both species, survival decreased with pH, with 100% mortality of red king crabs occurring after 95 days in pH 7.5 water. Though the morphology of neither species was affected by acidification, both species grew slower in acidified water. At the end of the experiment, calcium concentration was measured in each crab and the dry mass and condition index of each crab were determined. Ocean acidification did not affect the calcium content of red king crab but did decrease the condition index, while it had the opposite effect on Tanner crabs, decreasing calcium content but leaving the condition index unchanged. This suggests that red king crab may be able to maintain calcification rates, but at a high energetic cost. The decrease in survival and growth of each species is likely to have a serious negative effect on their populations in the absence of evolutionary adaptation or acclimatization over the coming decades.

Ocean acidification, a decrease in ocean pH due to absorption of anthropogenic atmospheric CO2, has variable effects on different species. To examine the effects of long-term exposure on Tanner crab (Chionoecetes bairdi) embryonic development, hatching success, and calcification, ovigerous females were reared in one of three treatments: ambient pH (∼8.1), pH 7.8, and pH 7.5 for 2 years. Embryos and larvae in year 1 were from oocytes developed in the field and appear resilient to high pCO2. Embryos and larvae in year 2 were from oocytes developed under high pCO2 conditions. Oocyte development appears sensitive to high pCO2, effects carryover and altered embryonic development, and reduced hatching success with on average 71% fewer viable larvae hatched in the pH 7.5 treatment than in the other treatments. Per cent calcium was reduced among females exposed to pH 7.5 waters, and their carapaces were noticeably more pliable than those in the other treatments. Softer carapaces may result in reduced defences against predators, and a reduction in the ability to feed on prey with hard parts such as shells. The results from this long-term study suggest that projected ocean pH levels within the next two centuries will likely have a pronounced impact on Tanner crab populations unless the crab are able to acclimatize or adapt to changing conditions.