Illustration of the biovolume calculations. (o) Case of a cell of Chlorella vulgaris which cell shape attribution in Appendix 1 is a sphere (a) Case of a cell of Cymbella which cell shape attribution in Appendix 1 is a box; a multiplicative factor of 0.7 is applied to the volume of the box to get the biovolume of the Cymbella cell. (b) Case of a mucilaginous Cyanobacteria colony. The first way to calculate the biovolume is to measure a cell dimension and calculate the biovolume of one cell based on a triaxial ellipsoidformula; the biovolume of one cell is multiplied by 13 (the number of cells in the colony) to get the colony biovolume. The second way is to measure the colony dimensions (taking into account the mucilage) and to calculate the biovolume of the colony based on a triaxial ellipsoid. Finally this volume is multiplied by a factor of 0.1 (the cell volume is estimated to be 10% of the mucilaginous colony) to get the colony biovolume. (c) and (d) give the case of a Scenedesmus coenobe biovolume calculation. The first way (c) to calculate the biovolume, is to measure the cell dimensions and to calculate its biovolume based on a triaxial ellipsoid ; then the cell biovolume is multiplied by 4 (4 cells in the coenobe) to get the coenobe biovolume. The second way (d) to calculate the biovolume, is to measure the coenobe dimensions; in this case the coenobe shape is associated to a box. The box volume is calculated. Since the coenobe volume is smaller than the box volume, the box volume is multiplied by a factor of 0.8 to get the coenobe volume (the coenobe volume is estimated to be 80% of the box).