Aragonite production by pteropod molluscs in the subarctic Pacific

Abstract

Daily aragonite production of thecosomatous pteropods in the subarctic Pacific was estimated using the instantaneous growth rate and size-frequency methods. At Ocean Sta. PAPA during July 1985, samples for production estimates of two pteropod species, Clio pyramidata and Limacina helicina, were collected in plankton tows using nets of different mesh sizes (303, 150 and 73 μm) to include all size classes of pteropods. Estimates of calcium carbonate biomass of C. pyramidata and Limacina helicina were 67 and 155 mg CaCO 3 m −2, respectively. For the instantaneous growth rate method, shell growth of C. pyramidata was measured in 45Ca uptake experiments with diver-collected animals. For L. helicina, the rate of shell calcification was calculated from literature values on changes in mean shell diameter and the allometric relationship between shell weight and shell diameter. Aragonite production, calculated by the instantaneous growth rate method, was 1.8 mg CaCO 3 m −2 d −1 for C. pyramidata and 2.6 mg CaCO 3 m −2 m −2 d −1 for L. helicina. In comparison, aragonite production estimated by the size-frequency method was 1.4 mg CaCO 3 m −2 d −1 for C. pyramidata. The aragonite production estimate of 4.4 mg CaCO 3 m −2 d −1, determined by the instantaneous growth rate method, was 50% of the published estimate of foraminifera flux collected in a deep sediment trap at Sta. PAPA during the time of this study. Based on a model of annual production, pteropod aragonite accounts for 4–13% of the estimated total CaCO 3 production of 12–20 g CaCO 3 m −2 y −1. Results of the model suggest that coccolithophorids are the major producers of CaCO 3 at Sta. PAPA, contributing 59–77% of the estimated total CaCO 3 production.