The Survival of Freshwater Algae During Dry Periods: Part I. An Investigation of the Algae of Five Small Ponds

Abstract

The information available regarding the survival of freshwater algae during dry periods is somewhat meagre. Text-books (Fritsch 1935; Smith 1938, 1951; West & Fritsch 1927) refer to 'resting cells', 'cysts', 'akinetes' and 'resistant stages' but with some exceptions little appears to be known in detail about the droughtsurvival value of these stages. Physiologically, a cell or a group of cells in which growth has ceased, temporarily at least, and in which the metabolic processes are at a minimum may be said to be a resting stage. This is a wide definition and includes such structures as resting oospores, zygospores, hypnospores and akinetes. For each algal species one or more of these stages might assist in the survival of the species during dry conditions. Str0m (1924), referring to the overwintering of algae, said that the importance of zygospores and other resting spores had been greatly exaggerated and also pointed out that it is incorrect to generalize, as species of a genus may differ widely in their reactions to any particular condition. Bristol (1920) found that algae surviving in old stored soils (26-73 years old) included members of the Cyanophyceae, the Chlorophyceae and one diatom, Nitzschia palea. Certain terrestrial algae have been investigated with regard to the survival of vegetative stages during drought by Fritsch (1922) and Fritsch & Haines (1923). Various references have been made to the accumulation of granular bodies or oil globules in organisms exposed to periods of desiccation (Denffer 1949; Fritsch 1916, 1944; Heide 1939; Kahn 1949; Petersen 1935; Piercy 1917; Salah 1952). Rao (1953) carried out some work on the algae of a pond which eventually dried up but he found no resting stages. Lund (1942) observed an immediate decrease in the algal flora of exposed pond-bottom deposits when the surface of the mud areas began to dry, but found no stages of the normally aquatic algae which he could