Abstract
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.