Abstract

Standard methods for sampling, fixation and quantification of organisms in highly acid environments with pH values at or below 3 are presented. Some important problems are discussed, together with recommendations on how to handle the material. Examples of specific problems are included, especially the effects of fixatives on the cell dimensions of species of Chlamydomonas, Oxytricha and Actinophrys, and on cell numbers of Actinophrys. Mixed populations of heterotrophic protists should be preserved with Lugol's solution, because other fixatives do not permit the recognition of heliozoans.