Phytoplankton net samples from all oceans were examined by advanced light microscopy or electron microscopy for the presence of 26 diatom species, and the records plotted on eight distribution maps. Some of the species are classified as cosmopolitan, some as warm-water species and some as cold-water species. The cold-water species belong either to the Northern Hemisphere or to the Southern Hemisphere, or are suggested as being bipolar, having a disjunct distribution. Some of the smallest marine planktonic diatoms collected have a cosmopolitan distribution. Thalassiosira species, forming gelatinous masses, seem to be most prominent in coastal waters where upwelling occurs. The distribution patterns of T. gravida and T. rotula indicate that they may be modifications of the same species. The finding of morphologically and taxonomically closely related species in distinctly different biogeographic regions emphasizes the importance of reliable identification at the specific level. |
