Eighteen marine species exposed to ocean acidification conditions for 60 days exhibited a wide range of responses. Ten of the 18 species were affected negatively with lower rates of net calcification and, in some cases, net loss of shell. Those species included temperate corals, pencil urchins, hard clams, conchs, serpulid worms, periwinkles, bay scallops, oysters, whelks, and soft clams. However, in seven species, net calcification increased under the intermediate and/or highest levels of ocean acidification. Those species included limpets, purple urchins, coralline red algae, calcareous green algae, crabs, lobsters, and shrimps. One species, the blue mussel, showed no response at all. The results suggest that the impact of ocean acidification on marine calcifiers is varied, and there are several causes of the variable impacts. (Laboratory study)