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.

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The structure of a cytochrome c(7) (PpcA) from Geobacter sulfurreducens was determined by X-ray diffraction at 1.45 A resolution; the R factor is 18.2%. The protein contains a three-heme core that is surrounded by 71 amino acid residues. An unusual feature of this cytochrome is that it has 17 lysine residues, but only nine hydrophobic residues that are larger than alanine. The details of the structure are described and compared with those of cytochrome c(7) from Desulfuromonas acetoxidans and with cytochromes c(3). The two cytochrome c(7) molecules have sequences that are 46% identical, but the arrangements of the hemes in the two structures differ; the rms deviation of all alpha-carbons is 2.5 A. These cytochromes can reduce various metal ions. The reduction site of the chromate ion in D. acetoxidans is occupied by a sulfate ion in the crystal structure of PpcA. We identified four additional homologues of cytochrome c(7) in the G. sulfurreducens genome and three polymers of c(7)-type domains. Of the polymers, two have four repeats and one has nine repeats. On the basis of sequence alignments, one of the hemes in each of the cytochrome c(7)-type domains does not have the bis-histidine coordination. The packing of the molecules in the crystal structure of PpcA suggests that the polymers have an elongated conformation and might form a "nanowire".

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