Stereology 



Quantitative estimates of cellular components were developed by techni- 

 ques described by Sicko-Goad et al_. (1977). Fifty micrographs were examined 

 for each experimental treatment analyzed. A transparent 12.5 mm square sam- 

 pling lattice was superimposed over the micrographs for point count measure- 

 ments. Although several sections were collected on one grid, only one sec- 

 tion per grid was used in the analysis. Blocks were retrimmed after each 

 series of sections had been cut in order to avoid repeated sampling of adja- 

 cent material within the same organism. For species where cells are con- 

 nected in a colony, only one cell per colony was included in the statistical 

 sample. 



RESULTS 



Figure 1 shows the distribution of Fragilaria capucina Desm. in southern 

 Lake Huron in June of 1974. This distribution is atypical in that this 

 species generally becomes abundant in areas of the Laurentian Great Lakes 

 which are severly eutrophied (Hohn 1969) but does not survive in the less 

 nutrient rich offshore waters. Electron micrographs of cells of this 

 species taken within Saginaw Bay (Figure 2) show that they contain numerous 

 small vacuolar inclusions having the general form and appearance of poly- 

 phosphate bodies. Although the formation of polyphosphate bodies has not 

 been widely reported in eukaryotic phytoplankton organisms. X-ray analyses 

 of the inclusions (Figure 3) confirm that their elemental composition is es- 

 sentially similar to that of polyphosphate bodies reported from prokaryotic 

 organisms (Sicko-Goad et aj_. 1975). The primary difference is that the 

 bodies found in Fragilaria capucina are much smaller than those found in 

 most prokaryotic organisms and that they are found within the vacuole of the 

 eukaryotic cells. 



X-ray spectra of the polyphosphate bodies found in Fragilaria capucina 

 in this locality also indicate the presence of appreciable quantities of Pb 

 as a constituent of the bodies (Figure 3). 



Observations of other eutrophication tolerant phytoplankton species in 

 Saginaw Bay indicated the widespread occurrence of polyphosphate bodies, 

 even in areas where chemical analyses of the water showed low levels of dis- 

 solved phosphorus in the water. Polyphosphate bodies were particularly ap- 

 parent in cells of some of the potentially nuisance producing blue-green al- 

 gae in the assemblages. These observations also show that the distribution 

 of populations containing polyphosphate bodies within the bay is restricted 

 primarily to stations along the southern and southwestern shore of the bay 

 (Figure 4) . 



Subsequent observations utilizing staining techniques which permit 

 visualization of polyphosphate bodies at the light microscope level (Ebel 

 et al_. 1958) show that polyphosphate bodies are developed in phytoplankton 

 populations present in several areas of the Great Lakes system which receive 

 relatively high loadings of phosphorus and other contaminants. 



175 



