Studies on the phytoplankton ecology of the Trondheimsfjord. I. The chemical composition of phytoplankton populations

Samples of phytoplankton populations from the Trondheimsfjord, collected in 1970 and the first five months of 1971, have been analysed for carbohydrate, protein, lipid, and phosphorus. Lipid was in all cases less than 10% of the organic dry matter. The $\text{N}\text{P}$ ratio was remarkably constant, but the ratio protein/carbohydrate varied between wide limits. For samples consisting mainly of dinoflagellates, the protein/carbohydrate ratio was always low, due to a large amount of insoluble polysaccharides, probably corresponding to material in the cell walls.For diatoms, the carbohydrates may conveniently be divided into three fractions: 1) an acidsoluble glucan of the β-1, 3-linked type; 2) an alkali-soluble fraction giving a complex mixture of monosaccharides on hydrolysis and, 3) an insoluble glucan. The amounts of acid-soluble glucan varied from 7.7 to 36.5% of organic dry matter and these changes are the main cause of the variation of the protein/carbohydrate ratio of diatom samples. For diatom samples this ratio is a valuable indicator of the physiological state of the population. The variations observed in this study are discussed.