Mats of colourless sulphur bacteria. II. Structure, composition of biota and successional patterns

Mats of colourless sulphur bacteria from a relatively exposed shallow water sediment and from a deeper, more protected sediment were studied. In the exposed habitat, patches of white sulphur bacteria had a limited lifet~me and displayed a characteristic succession in which small sulphur bacteria (Thiospira, Macrornonas) dominated at f~rst followed by Thiovulurn, which was eventually displaced by Beggiatoa; during summer phototrophic organisms dominated. Th~ovulum films were only -0.2 mm thick and the projected area of the cells covered only 7 to 36% of the sediment surface while mats of filamentous bacteria were thicker and represented a higher biomass. In the protected locality the Beggiatoa mats were -0.6 mm thick and represented a 10-fold higher biovolume than those from the exposed h a b ~t a t .