In a wet environment where sunlight is the main source of energy, the uppermost layers are generally dominated by aerobic photosynthesizing cyanobacteria (blue-green bacteria whose color is caused by their having chlorophyll), while the lowest layers are generally dominated by anaerobic sulfate-reducing bacteria.
Nun ambiente húmido no que a luz é a principal fonte de enerxía, as capas superiores están xeralmente dominadas por cianobacterias fotosintéticas aerobias (bacterias azul-verdosas cuxa cor está causada pola clorofila que teñen), mentres que as capas inferiores están xeralmente dominadas por bacterias redutoras de sulfato anaerobias.