Epiphytic algae on the bulrush (Scirpus californicus (Mey) Steud) in the Rio de la Plata (Argentina): structure and architecture

Abstract

The objective of this study is to determine which are the characteristic algal communities coating the stems of Scirpus califomicus (MEY) STEUD in the Rio de la Plata. Taxonomic composition, disposition of the algae in the biofilm, spatial patterns of abundance and species diversity and life-form strategies were analysed. Samples of periphyton were taken in winter and spring 1999 and summer and autumn 2000, at five sampling sites. Physical-chemical characteristics were measured in summer and autumn 2000. Ten stems of the bulrush were cut randomly and the bottom 15 cm kept and put into a flask with distilled water. The biofilm was removed by brushing, integrating the material collected in each sampling site. The algae that comprised the biofilm analysed showed a simple architecture consisting of a layer dominated mainly by biraphid diatoms, with planktonic diatoms and/or filamentous chlorophytes entrapped in the surface film. The matrix analysed in this study corresponds to early stages of succession characterized by R-selected taxa, considered to be pioneer species and good colonizers in a disturbed system. During spring, winter and autumn, diatoms were dominant, but with different species compositions, while in summer green algae were abundant. The epiphyton of the bulrushes studied was characterized by a low proportion of epiphytic specimens sensu strictu (adnate, stalked and erect forms) exhibiting a high proportion of immigrants from the benthos and plankton.