Strategies providing success in a variable habitat: I. Relationships of environmental factors and dominance of Cladophora glomerata

Dominance of macrophytes and their response to environmental factors were s tudied in the river Ilm, Thuringia/ Germany with special reference to Clado pkora glomerata (L,) Kutz, Macroalgae showed a growth peak in spring with C , glomerata, Ulothrix zonata Kutz,, Lemanea fluviatilis (L,) C, Agardh and Audouinella sp, being the dominant species. Shortly after this peak, a rapi d decline of macrophyte substrate coverage was observed. Only C. glomerata revealed a second growth peak in late summer/early autumn. Frequent disturb ances of the macrophyte assemblage by floods resulted repeatedly in an almo st complete wash out of benthic organisms. After summer floods C, glomerata was the species that recolonized the substrate. At high-light sites, faste r recovery of C, glomerata was observed as compared to low-light sites. Thi s is discussed in relation to the life cycle of C, glomerata, Among the phy sical and chemical parameters that were analysed, irradiance, current veloc ity, pH, soluble reactive phosphorus and ammonia-nitrogen accounted for mos t of the observed patterns of dominance of C, glomerata.