SHORT COMMUNICATION Carbon and nitrogen content of Noctiluca scintillans in the Seto

Abstract. The carbon and nitrogen content of Noctiluca scintillans cells from the Seto Inland Sea, Japan was investigated in order to estimate its biomass in natural samples. The carbon content of N.scintillans ranged from 123 to 627 ng C cell–1 with a mean value of 353 ng C cell–1, or 1.12 to 2.67 fg C µm–3 with a mean value of 1.98 fg C µm–3. The nitrogen content ranged from 36.0 to 232 ng N cell–1 with a mean value of 131 ng N cell–1, or 0.499 to 0.910 fg N µm–3 with a mean value of 0.694 fg N µm–3. Total cell carbon and nitrogen increased but the carbon and nitrogen per cell volume decreased with increasing cell volume. The C/N ratio of the cells ranged from 2.3 to 4.4, which was relatively low compared with the Redfield ratio. The carbon and nitrogen content was extremely low (91.2 ng C cell–1, 41.8 ng N cell–1) for starved cells, whereas it was extremely high (528 ng C cell–1, 205 ng N cell–1) for cells which had ingested the large diatom, Coscinodiscus wailesii. Our results suggest that the carbon and nitrogen content of N.scintillans varies depending on its physiological condition and the type of food that it has recently consumed. Noctiluca scintillans is a large, heterotrophic dinoflagellate which commonly forms red tides in temperate and subtropical coastal regions and which is well known for its luminescence. Although N.scintillans is classified as a flagellate, it does not contain photosynthetic pigments and feeds on phytoplankton and detri-tus using its tentacle (Fukuyo et al., 1990). Morphological studies of this species have been reported previously [e.g. (Zingmark 1970; Sweeny, 1976)]. Noctiluca scintillans feeds on the eggs of copepods and anchovies (Hattori, 1962; Sekiguch