Epiphytic algae and macroinvertebrates on submerged and floating-leaved macrophytes in an Italian lake

1. The presence of contiguous beds of submerged (Myriophyllum spicatum, Ceratophyllum demersum and Najas marina) and floating-leaved (Trapa natans) vegetation in a north Italian lake allowed us to test the effect of the different host architecture on epiphytic algae and invertebrates and to predict the consequences for the lake of changes in the predominant vegetation. 2. Epiphyton development, measured as carbon, nitrogen, phosphorus, chlorophyll a (Chl a), phaeophytin and as algal and macroinvertebrate density, was significantly higher on submerged plants than on T. natans. The C:Chl a ratio, a proxy of the ratio of heterotrophs to autotrophs, was higher on the floating-leaved plants. The elemental (C:N:P) and pigment (Chl a:phaeophytin) ratios were not significantly different between the two vegetation types. 3. The taxonomic composition of epiphytic algae and invertebrates was similar on the different plants. The more varied morphology of the floating-leaved T. natans resulted in a higher diversity of epiphytic algae, however, but not of macroinvertebrates. 4. There was a significant inverse relationship between epiphyton biomass and the standing crop of the host plant, suggesting a key role for light and water exchange in epiphyton development. 5. Replacement of: floating-leaved by submerged plants would increase the total biomass of epiphytic algae and invertebrates.