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Abstract

terrelations between plankton communities and dissolved carbohydrates and amino acids were investigated
under near-natural conditions in sea water enclosed in plastic tanks. In summer 1972 the development of a natural plankton
population was followed in a 3-m3 plastic tank for 28 d. In the course of this experiment, concentrations of dissolved neutral
carbohydrates and free amino acids were determined. Results are in the range of published data for the open sea with respect to
concentrations (0.2-2.5 pnoles dm-3 total sugar; 0.2-3.1 pnoles dm3 total amino acids) and qualitative composition. A plankton
succession was observed during the experiment; this was accompanied by distinct alterations in the concentrations of dissolved
amino acids and carbohydrates. Glucose and lysine occurred in highest concentrations. Maximum rate of increase was 29 nmoles
dm3 h-' for glucose, and 25 nmoles dm3 h-' for lysine. The rates of decrease are in the same range as bacterial uptake rates
determined by various authors employing tracer methods. Numerous positive, highly significant correlations suggest heteropoly-
saccharides as one source of individual carbohydrates. Relations between certain species within the plankton succession and
occurrence of dissolved organic substances were observed. Significant positive correlations existed between glucose and
diatoms as well as between glucose, galactose, mannose, arabinose and ribose and phytoplankton biomass. There were also
several significant positive correlations of amino acids, especially of valine, leucine and isoleucine with other biological
parameters.