Light micrograph of marine diatoms Parlibellus sp. Parlibellus diatoms live in large numbers of individuals in muco-polysaccharide tubes, attached to rocks and other submerged substrates. The tufted colonies can easily be mistaken for brown algae; only under the microscope can the diatoms be recognized. The samples are from the North Sea, German Bight. The relatively cool northern seas harbour very large quantities of these primary producers, which autotrophically form the base of the food chain. At the same time the diatoms of the oceans form about 45% of the oxygen worldwide. Microscopic contrast method : Differential interference contrast. Magnification 200x at a print width of 10 cm.