Nutrient induced changes in the species composition of epiphytes on Cladophora glomerata Kutz. (Chlorophyta)

Cladophora glomerata is a widely distributed filamentous freshwater alga th at hosts a complex microalgal epiphyte assemblage. We manipulated nutrients and epiphyte abundances to access their effects on epiphyte biomass, epiph yte species composition, and C. glomerata growth. C. glomerata did not grow in response to these manipulations. Similarly, nutrient and epiphyte remov al treatments did not alter epiphyte biovolume. Epiphyte species compositio n, however, changed dramatically with nutrient enrichment. The epiphyte ass emblage on unenriched C. glomerata was dominated by Epithemia sorex and Epi themia adnata, whereas the assemblage on enriched C. glomerata was dominate d by Achnanthidium minutissimum, Nitzschia palea and Synedra spp. These res ults indicate that nutrients strongly structure epiphyte species compositio n. Interactions between C. glomerata and its epiphytes were not affected by epiphyte species composition in our experiment but may be when C. glomerat a is actively growing.