ABSTRACT
Microscopic analysis can be used to determine both the community structure and the biomass of the planktonic autotrophs in the sea. Electron microscopy allows such identification of many of the pico- and nanoplankton-sized organisms. From cell concentrations and dimensions, estimates of biomass can be made using standard conversions from volume to carbon. As cumbersome as such an approach may seem the alternatives are clearly more limited in scope: for example, biomass of the entire autotroph assemblage can be estimated from concentrations of chlorophyll a in the sample, but only if the carbonxhlorophyll a ratio for that time and place is known. One advantage of the microscopical method is greater biological detail for the whole size spectrum of microbial autotrophs. If care is taken in selecting sample sizes, especially for the larger cells (LM), summation of the biomass of the individual size fractions is an accurate estimate of the total autotroph carbon.
