In 2007, first-sale revenues from U.S. commercial fisheries totaled about $4 billion. Four groups of animals contributed almost equally to that total. Two groups are calcifiers, which means they make shells, spines, or exoskeletons out of calcium carbonate: crustaceans (lobsters, crabs, shrimp) and mollusks (clams, oysters, mussels, scallops, and other non-crustacean calcifiers). The other two groups are animals that prey on calcifiers (such as flounder and octopus) and top predators that eat the calcifiers’ predators (such as salmon and tuna). Of these groups, the mollusks appear most vulnerable to direct effects of ocean acidification. But a decline in those species could cause problems for predators above them on the food chain.[back]
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