Nature: Fish may contribute to the ocean carbon cycle in a previously unsuspected way. Traditionally, scientists have attributed the production of calcium carbonate in surface waters to marine plankton. But a study led by Rod Wilson at the University of Exeter, UK, now shows that fish excrete the mineral as a by-product of drinking seawater. Wilson and his colleagues measured the rate at which fish excrete calcium carbonate from their intestines and then combined this with two independent …