Carbon to volume relationships for dinoflagellates, diatoms, and other protist plankton

Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume (C:vol) and nitrogen to volume (N:vol) relationships. Cellular C and N content ranged from 48 to 3.0 × 10 4 pgC cell −1 and 11 to 2,656 pgN cell −1 for cells ranging in volume from 180 to 2.8 × 10 5 µm 3 . C and N density in dinoflagellates decreased significantly with increasing cell volume. C:N ratios ranged from 3.44 to 6.45. C:vol and N:vol in dinoflagellates are significantly related as expressed by the equations pgC cell −1 = 0.760 × volume 0.819 and pgN cell −1 = 0.118 × volume 0.849 . Previously published data were combined to compare C:vol relationships in different phylogenetic protist groups, including chlorophytes, chrysophytes, prasinophytes, and prymnesiophytes. Our analysis indicated differences between the C:vol relationships available for ciliates. A new C:vol relationship for diatoms was established (pgC cell −1 = 0.288 × volume 0.811 ). Dinoflagellates are significantly more C dense than diatoms. Except for diatoms, we found few significant differences between C:vol relationships of different phylogenetic groups. Consequently, one C:vol relationship for taxonomically diverse protist plankton excluding diatoms was determined (pgC cell −1 = 0.216 × volume 0.939 ). In the combined data set, carbon density was not constant but decreased significantly with increasing cell volume. Using constant C:vol conversion factors for plankton over large size ranges will cause systematic errors in biomass estimates.