PRIMARY COLONIZATION BY MICROALGAE IN RELATION TO SPATIAL VARIATION IN EDAPHIC FACTORS ON ANTARCTIC FELLFIELD SOILS

1. The causes of variations in the composition of microalgal communiti es on frost-sorted soil polygons on Signy Island, maritime Antarctica, were investigated, based on analyses of physical and chemical conditi ons and microalgal communities from 65 polygons. 2. Interpolygon varia tions in all environmental factors measured were small and not much gr eater than the intrapolygon variations. Microalgal diversity was low. Only seven taxa occurred in sufficient numbers to be included in stati stical analyses, two of which, Nostoc spp., were found on only one pol ygon. The filamentous cyanobacterium Phormidium autumnale occurred on all polygons and usually provided the largest component of the total b iovolume. 3. Microalgal communities were qualitatively constant within polygons, but varied markedly between polygons. Principal components analysis indicated that each taxon varied independently of the others, and hence it was not possible to correlate community structure with a ny specific environmental factor. 4. Correlations between numbers of i ndividual taxa and edaphic factors were low and accounted for a maximu m of 18% of the observed interpolygon variation or 12% of the total va riation. It is suggested that the observed differences in the microalg al communities were due to the vagaries of the colonization process an d reflect the probability of successful colonization of these ecosyste ms by microalgae.