Vertical and seasonal distri bution of epiphytic algae on water chestnut (Trapa natans)

Abstract

Changes in density, biomass, Shannon-Wiener diversity and equitability of epiphytes on different parts of Trapa natans (lamina, petiole, stem and roots) are described during the life cycle of this floating-leaved aquatic plant in the shallow eutrophic lake, Lago di Candia, northern Italy. The seasonal standing crop of epiphyton paralleled that of water chestnut, although the maximum biomass of epiphyton preceded by one month that of the host plant. Epiphytic algal succession moved from prostrate chlorophytes and adnate diatoms towards basally attached species and later to filamentous cyanophytes. Epiphytic algal assemblages showed clear differences according to the different plant parts and depths. There was a decrease in the mean abundance, biomass and cell size of epiphytes from upper to lower parts of the plant and species succession in lower parts was delayed and shortened compared with that in the upper parts. There was a greater presence of filamentous green algae, desmids and filamentous N 2 -fixing cyanophytes on the lamina and petiole than on the stem and roots, where communities were mostly comprised of small diatoms and a filamentous cyanophyte. Species dynamics on stem and roots situated at the same depths were similar. Several factors accounted in determining the composition and abundance of epiphytic communities, such as plant architecture and age, and physicochemical variables, such as light within the Trapa belt.