EPILITHIC ALGAE FROM A FRESH-WATER STREAM AT HOPE-BAY, ANTARCTICA

Temporal and spatial variations of the epilithic phycoflora were studi ed in one of the largest streams at Hope Bay (Antarctic Peninsula) dur ing the summer of 1992/93. A complete floristic inventory was made, an d the relative frequencies of each algal taxon were estimated. Periphy tic cumulative chlorophyll a was measured by means of artificial subst rata. The stream was a typical maritime Antarctic lotic ecosystem, wit h evident signs of enrichment by sea-birds. Variability in discharge s trongly affected the water chemistry, with the high water level period s characterized by the lowest conductivities and dissolved reactive ph osphorus concentrations. Epilithic algal communities predominantly con sisted of algal mats or filamentous and foliose forms of Prasiola cris pa. Other dominant species were Leptolyngbya fragilis, Hydrurus foetid us, Chrysococcus cf. rufescens and Phaeogloea mucosa. Whereas P. crisp a appeared more frequently near to the origin of the stream in Boeckel la Lake, Chrysophyceae were better developed towards the mouth.