Estimation of amoeba cell volume from nuclear diameter and its application to studies in protozoan ecology

To facilitate the estimation of cell volume in uninucleate, naked amoebae (gymnamoebae) the relationship, log cell volume (µm³) = 0.882 + 3.117log nuclear diameter (µm³), is presented. This links mean cell volume to mean nuclear diameter and provides a useful tool for protozoan ecologists interested in estimating the biovolume of amoebae in laboratory or field samples. While it is virtually impossible to measure rigid axes from which volume can be calculated in these amorphous cells, it is relatively easy to measure the diameter of the nucleus in living or fixed material. This relationship has shown that most uninucleate amoebae surveyed have volumes ranging between only 188 µm³ and 2860 µm³; this range reflects the volumes of the majority of amoebae in the field. These small volumes are unexpected since many amoebae have locomotive forms greater than 20 µm in length giving the impression that their cell volumes should be correspondingly large. This is not the case, however, because most amoebae are extremely flat when viewed in profile. The small cell volume of most amoeba species has ecological implications when numerical data is transformed to biovolume and biomass units.