Ecology of benthic diatoms from Lake Macro Prespa (Macedonia)

Abstract

Lake Prespa belongs to the group of ancient lakes. By subterranean channels it is connected with Lake Ohrid. In the past two decades, Lake Prespa has been characterized by a decrease of its water level and an increased cultural and natural eutrophication. In this period, very few ecological studies were performed, based mainly on composition and biomass of the phytoplankton community. From June 2002 to May 2003 analyses of 18 physical and chemical parameters and composition of benthic diatoms were performed on 12 sampling sites of Lake Macro Prespa. About 300 diatom taxa were identified in the lake. Relative abundances were calculated by counting 200 diatom valves, and 143 diatom taxa had abundances of more than 1 % in at least one sampling site. Deep benthic communities were dominated by Cyclotella ocellata and Diploneis mauleri, while in the littoral region these communities were dominated by small Navicula sensu lato species. For statistical analyses, the 17 most abundant diatom taxa (> 1 % in total abundance) were used. Contrarily to the expectations, TP had a negligible influence on diatom community structure. The main environmental factors controlling species distribution and abundances were ammonium and metallic cations (Cu, Mn, K) and, secondarily, dissolved oxygen and Secchi depth, as inferred from both correlation and multivariate (CCA) analysis.