ABSTRACT
Although bacterial biomass generally represents only a small amount of particulate organic carbon, it is of paramount importance, especially with regard to its role in microbial food webs. Therefore, the argument which proposes a constant carbon value for bacteria regardless of their size should be put at rest because it has no biochemical or physiological basis, and also ecological studies suggest that cell size is a significant indicator of the nutrient status and activity of bacteria. Before setting a threshold, however, some other segmentation routines may be used to improve contrasts, to define edges, to remove noise, to detach adhering cells, etc. As a minimal treatment before thresholding, averaging may help to remove some noise without changing size and aspect ratio of small objects. The measurement is what quantitative image analysis is all about. It may include determination of the "roughness" of objects by consecutive erosions and measurements with masks of different size, shape, and loading factor.
