RESEARCH PAPER Spatial and temporal dynamics of the steady-state phytoplankton assemblages in a temperate shallow hypertrophic lake (Lake Manyas, Turkey) Kemal C ¸ elik Æ Tug ˘ba Ongun Received: 26 July 2007 / Accepted: 25 October 2007 / Published online: 19 March 2008 Ó The Japanese Society of Limnology 2008 Abstract Spatial and temporal dynamics of phytoplank- ton biomass and species composition in the shallow hypertrophic Lake Manyas, Turkey, were studied biweekly from January 2003 to December 2004 to determine steady- state phases in phytoplankton assemblages. Steady-state phases were defined when one, two or three coexisting species contributed to at least 80% of the standing biomass for at least 2 weeks and during that time the total biomass did not change significantly. Ten steady-state phases were identified throughout the study peiod. During those periods, Achnanthes microcephala (Ku ¨tzing) Cleve twice domi- nated the phytoplankton biomass alone and contributed to more than 50% of the total biomass in seven phases. Microcystis aeruginosa (Ku ¨tzing) Ku ¨tzing, Anabaena spiroides Klebahn, Cyclotella stylorum Brightwell, Pedia- strum boryanum (Turpin) Meneghini and Phacus pusillus Lemmermann were also represented once in steady-state phytoplankton assemblages. A. microcephala was domi- nant usually during cold periods of the year, while M. aeruginosa and A. spiroides were usually dominant in warm seasons. The total number of species showed a clear decrease during steady-state phases at all stations. All stations were significantly different in terms of the mea- sured physical and chemical parameters (P \ 0.05) and phytoplankton biomass (F = 117, P \ 0.05). Keywords Phytoplankton Á Shallow temperate lake Á Steady-state Introduction There are more shallow lakes than deep lakes worldwide. Such lakes, used for drinking water, irrigation, fisheries and recreation, are more affected by human activities than deep lakes. The socioeconomic importance of shallow lakes calls for more scientific research on these systems (Padisak and Reynolds 2003). In the last 2 decades, a number of studies have dealt with steady-state phytoplankton assemblages in various types of water bodies (Feuillade and Feuillade 1987; Davidson et al. 1999; Huszar et al. 2003; Naselli-Flores et al. 2003; Moustaka-Gouni et al. 2007). Such studies contributed to the understanding of the equilibrium concept in phyto- plankton ecology. For identification of steady-state phases, Sommer et al. (1993) set three criteria: (1) a maximum of three species contribute more than 80% of total biomass, (2) their dominance lasts for more than 2 weeks, and (3) during the 2-week period, the total biomass does not change significantly. Selection of dominant phytoplankton species in lakes usually depends upon unpredictable and complex combi- nation of factors, including the physical structure of the system, the availability of nutrients, and the biotic inter- actions (Padisak et al. 2003; Nixdorf et al. 2003). Steady- state phases of phytoplankton aasemblages occur quite rarely in oligo- or mesotrophic lakes, but such phases dominated by cyanoprokaryotes are often seen in hyper- trophic conditions in stressed shallow water bodies and usually occur in summer or late summer (Stoyneva 2003; Padisak et al. 2003; Nixdorf et al. 2003). Although phytoplankton studies have increased since the end of the last century, the knowledge of steady-state phytoplankton ecology in temperate lakes is still far from complete. The objectives of this study were to identify the K. C ¸ elik (&) Á T. Ongun Department of Biology, Faculty of Arts and Science, Balıkesir University, 10145 Balıkesir, Turkey e-mail: kcelik@balikesir.edu.tr 123 Limnology (2008) 9:115–123 DOI 10.1007/s10201-007-0233-1