Studies on the terrestrial and freshwater algae of aldabra atoll

Abstract

A study was made of the terrestrial and freshwater algae of Aldabra Atoll, Indian Ocean. Field work was carried out between September 1972 and June 1973. Wide ranging excursions were made to various areas of the atoll in order to collect information on the species present together with physico-chemical and descriptive data from representative habitats. Data were collected in a standard manner and stored in a computable form using a modified version of a stream recording system devised in Durham, 1053 samples were collected during the field study, of which 521 were complete with detailed taxonomic and environmental data. The latter are stored on computer file at Durham. The 521 samples constituted an Aldabran data bank and a range of computer programmes facilitated the rapid retrieval of information and the performing of statistical analyses. An example of one such statistical analysis is included in the present study. A taxonomic checklist is given of the 291 species together with descriptions of these species, comparisons with the descriptions given by other authors, the areas of Aldabra from which they were recorded, notes on distribution on Aldabra, habitats, abundance and comparisons with records of other workers. Blue-green algae are the most abundant species present, predominating in both terrestrial and freshwater habitats. In terrestrial habitats they are often present almost to the exclusion of other species, though in freshwater habitats this predominance is less well-marked. It is probable that some species are restricted to certain regions or habitats: the reasons for such restriction are discussed. A study of one physiological process in blue-green algae is presented. The nitrogen-fixing potential of Tolypothrix byssoidea and several Nostoc species was investigated using the acetylene reduction assay technique. The study includes rates measured between 0930 and 1200 h, a 24 h time course study for Nostoc Commune and laboratory studies on the onset of acetylene reduction after rewetting.