Fixation artifacts of phytoplankton in zooplankton grazing experiments

The influence of various fixatives on size distribution and cell concentration was investigated using two types of electronic particle counters. Both in autotrophic and heterotrophic flagellates drastic losses of cells and changes of size were found in all preservatives used. Also preserved natural seston samples were not representative of the original fresh sample, and they continued changing and varying in the course of time. In diatoms also changes in size were noticed due to the fixative, however, doubt arises whether they were real or only measured differently by the particle counter. Even filtered sea water could not be preserved without obvious changes in particle distribution. Apart from diatoms, commonly used fixatives must be regarded worthless to preserve most phytoplankton and protozooplankton species in grazing experiments with zooplankton.