OSTRACODA (ISO15) Ecological requirements of Ostracoda (Crustacea) in a heavily polluted shallow lake, Lake Yenic ¸ag ˘a (Bolu, Turkey) Okan Ku ¨ lko ¨ ylu ¨ og ˘lu Muzaffer Du ¨ gel Mustafa Kılıc ¸ Ó Springer Science+Business Media B.V. 2007 Abstract Although the area of Lake Yenic ¸ag ˘ a is a potential candidate for RAMSAR convention, several anthropogenic factors compromise its biological diversity. This is mostly due to nutri- ent-rich water released from both point and nonpoint sources. Thirteen ostracod taxa (Can- dona neglecta, C. candida, Ilyocypris bradyi, Dar- winula stevensoni, Cypridopsis vidua, Physocypria kraepelini, Cypria ophtalmica, Prionocypris zenk- eri, Eucypris virens, Herpetocypris reptans, Pseudocandona compressa, Fabaeformiscandona fabaeformis Potamocypris cf. fulva) were found during this study. Potamocypris cf. fulva is a new record for the Turkish freshwater ostracod fauna. The first nine of these species have broad geographic ranges, implying high tolerance levels to different environmental variables. Based on the estimated species optima and tolerance levels, two species exhibited higher effective number of occurrences (C. neglecta, and D. stevensoni, respectively) than the other species. Three species (C. neglecta, D. stevensoni, I. bradyi) did not show significant correlation with any environ- mental variable we used. Both Canonical corre- spondence (CCA) and Pearson correlation analyses showed that temperature was the most effective predictor of species occurrence, fol- lowed by electrical conductivity and redox poten- tial. In contrast, pH and dissolved oxygen of water were the least effective predictors. Approx- imately 71% of the correlation between commu- nity composition and environmental variables was explained by the first axis of the CCA diagram, which had a relatively low (7.7%) cumulative variance of species. The lower (560 lg/l) and the upper (2030 lg/l) levels of ammonia (NH 3 ) exceeded the limits during winter season. The concentrations of total coliform and Escherichia coli bacteria were measured up to 10 · 10 7 cfu/ml and 10 · 10 3 cfu/ml, respectively. Results of phys- icochemical measurements, microbiological counts, and species data indicate that water quality of Lake Yenic ¸ag ˘a has been rapidly dete- riorated by anthropogenic factors that are the main threat for not only the lake’s aquatic diversity but also human health around the lake. Keywords Ostracoda Á Tolerance Á Optimum estimates Á CCA Á Conservation Á Eutrophication Guest editors: R. Matzke-Karasz, K. Martens & M. Schudack Ostracodology – Linking Bio- and Geosciences O. Ku ¨ lko ¨ ylu ¨ og ˘lu (&) Á M. Du ¨ gel Department of Biology, Faculty of Arts and Science, Abant _ Izzet Baysal University, 14280 Go ¨ lko ¨ y, Bolu, Turkey e-mail: kulkoyluoglu_o@ibu.edu.tr M. Kılıc ¸ Department of Biology, Zoology Building, Faculty of Science, _ Istanbul University, 34650 Beyazit, Istanbul, Turkey 123 Hydrobiologia (2007) 585:119–133 DOI 10.1007/s10750-007-0633-6