The survival of fresh water algae during dry periods

An investigation which has tended to be extensive rather than intensive, of the survival of fresh water algae during dry periods has been carried out. From April 1953 to June 1955, five small ponds, two in Hertfordshire, two in Middlesex and one in Surrey, have been visited regularly. At these ponds, water levels, water temperatures and the pH of the water and marginal litter or mud were recorded. Litter and mud samples were taken for the estimation of moisture content. Water samples and samples of litter and mud exposed above the water level were collected and examined for algae. In addition, throughout the period of the whole investigation, samples of water, litter and mud have been taken from various other habitats at irregular intervals. A series of large- and small-scale drying experiments have been carried out to investigate the reactions of various algae to drought and the survival of species through drought periods. Some investigation was made of the stratification of algae in pond margin litter and mud. Two methods were employed, a buried-slide technique and a micro-sampling technique. The observations made suggest that certain algae are capable of surviving dry periods by methods other than by the existence of resistant spores. It has been found that more or less obviously modified vegetative cells of a number of algae will survive drought. Further, certain algae, both motile and non-motile, have been found to survive in the deeper layers of litter and mud at pond margins during exposure and drying. While an attempt has been made to cover an extensive field, more detailed observations have been made on a number of individual species of algae.