Epilithic communities in a lake littoral zone : the role of water-columntransport and habitat development for dispersal and colonization of meiofauna

During the past 30 y, periphyton has been recognized as a key component in the benthos of lake littoral zones. However, the role of meiofauna-sized organisms living in the periphyton and mechanisms regulating and influencing those communities largely have been neglected, and the process of community development and colonization pathways of periphytic meiofauna are unknown in lakes. We studied these processes on littoral hard substrates in an oligotrophic lake. We manipulated the access of meiofauna to artificial hard substrates for a period of 57 d in a field experiment. In one treatment, the direct colonization pathway via active crawling was prohibited by elevating substrates into the water column. Development of the meiofaunal community was compared between elevated and nonelevated (control) treatments. In addition, relationships among the meiofaunal communities on the substrates in the field experiment and those in sediment traps and on natural hard substrates were examined. Periphyton biomass (chlorophyll a, total organic matter) and inorganic matter increased significantly in both experimental treatments throughout the experiment. Meiofauna colonized the substrates quickly and reached maximum densities of 107 ind./cm². The initial colonization phase (2 8 d) was characterized by a great variation in meiofaunal community structure; rotifers and crustaceans were the most abundant groups. Communities became less variable during the experiment and resembled natural communities on hard substrates at the end of the experiment. In general, development of meiofaunal abundance and periphyton biomass was rapid and proceeded similarly in both treatments. Our results show that colonization of littoral hard substrates can be driven by water-column transport of meiofauna and point to the importance of this pathway for dispersal and colonization of hard substrates by meiofauna