RNA/DNA ratios and DNA concentrations as indicators of growth rate and biomass in planktonic marine organisms

RNA and DNA concentrations were measured by a modification of the ethidium bromide method in batch cultures of marine phytoplankton and in natural plankton populations (1 to 333 v) from Dabob Bay, Washington State, USA, in spring and summer of 1981. In the cultures the DNA/C ratio remained nearly constant during all phases of growth and growth rate was linearly related to the RNA/DNA ratio. The DNA/C ratio and the relationship between growth rate and RNA/DNA ratio for cultures was used to estimate the amount of living biomass and the growth rates for plankton populations of Dabob Bay. The amount of living carbon was never 4 divisions d-'. Some of the potential problems with such calculations, for example, occurrence of detrital DNA, variability in the D N N C ratio for different groups of organisms, and differences in the relationship between growth rate and RNA/DNA ratio, are discussed. However, these problems may not be major obstacles to using DNA concentrations and RNNDNA ratios for answering major questions in biological oceanography.