Adaptations of epipelic and epipsammic freshwater algae.

Epipelic algae live freely on sediment surfaces, epipsammic algae live attached to grains in sandy sediments. Both groups may be buried by wave action and animal disturbance when they may find themselves in dark, deoxygenated layers. Epipelic algae, though tolerant of darkness for many days do not survive anaerobiosis for long and must rely on rapid movement to regain the sediment surface. Since they often are non-motile epipsammic algae cannot always move rapidly upwards. They tolerate both darkness and anaerobiosis, retaining considerable photosynthetic potential for several days in the complete absence of oxygen.