Respiration and calcium carbonate production by the invasive Asian clam, Potamocorbula amurensis, were calculated to assess their importance as CO 2 sources in northern San Francisco Bay. Production, calculated using monthly population density and size structure measured at three sites over 7 yr and a shell length/CaCO3 conversion factor, averaged 221 (??184) g CaCO3 m-2 yr-1. Net calcium carbonate production by this exotic bivalve releases CO2 at a mean rate of 18 (??17) g C m-2 yr-1. Respiration by P. amurensis, estimated from secondary production, releases additional CO 2 at a mean rate of 37 (??34) g C m-2 yr -1. Therefore, total net CO2 production by P. amurensis averages 55 (??51) g C m-2 yr-1 in an estuarine domain where net primary production consumes only 20 g inorganic C m -2 yr-1. CO2 production by P. amurensis in northern San Francisco Bay is an underestimate of the total CO2 supply from the calcified zoobenthic communities of San Francisco Bay, and results from other studies have suggested that this rate is not unusual for temperate estuaries. Global extrapolation yields a gross CO2 production rate in the world's estuaries of 1 ?? 1014 g C yr-1, which suggests that calcified benthic organisms in estuaries generate CO2 equal in magnitude to the CO2 emissions from the world's lakes or from planetary volcanism (the net source is determined by the highly variable rate of CO2 consumption by carbonate dissolution). This biogenic CO2 source is increasing because of the continuing global translocation of mollusks and their successful colonization of new habitats.
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Clams as CO2 generators: The Potamocorbula amurensis example in San Francisco Bay