Effects of limnoecological changes on the Ostracoda (Crustacea) community in a shallow lake (Lake Çubuk, Turkey)

We sampled Lake Çubuk, a shallow lake in Bolu (Turkey), for 26 months to investigate the effect of limnoecological changes on the composition of ostracod species. Seventeen ostracod species were identified from the six stations sampled between 2008 and 2010. Numbers of species and individuals were both significantly reduced during 2010, which corresponded to a 3 m water level increase. Ostracod Watch Model (OWM) displayed distinct seasonal occurrences of five species (Candona neglecta, Cypria ophtalmica, Cypridopsis vidua, Limnocythere inopinata, Fabaeformiscandona cf. japonica) when Physocypria kraepelini was the only species encountered all year round. Approximately 77.2% of the relationship between species and environmental variables was expressed by the first two axes of Canonical Correspondence Analysis (CCA). Electrical conductivity and water temperature (P = 0.002) were the most influential variables on species. There was a significant negative correlation of seven species to conductivity. Of those (F. cf. japonica and C. vidua) showed a significant positive correlation to water temperature, while C. candida was negatively correlated to water temperature (P < 0.05). C. neglecta was the only species to show a positive correlation to dissolved oxygen. Tolerance limits for the most common species were higher than the mean water temperatures, but lower than mean levels of electrical conductivity. Finding the ratio of noncosmopolitan to cosmopolitan species “pseudorichness” as 1.13 suggested significant role of cosmopolitan species to species diversity.