No abstract

We collected rotifers during one year (2002)(2003) from three different sites in the Pertek region of Keban Dam Lake. In total, 20 species belonging to 15 genera of 1 1 eurotatorian families were identified. The highest total rotifer abundance (346,667 individuals/m3) was recorded in December, while the lowest total abundance (7,640 individuals/m3) was seen in February. The densities of most rotifer species were highest in the spring months. Species richness was related directly to rotifer abundance. Rotifers were dominated numerically by two species, Polyarthra remata and Polyarthra vulgaris (14.9% and 14.4% respectively). Species abundance was positively related to temperature.

The present work tested the food selectivity of the cladoceran Ceriodaphnia quadrangula (O. F. Müller, 1785) and its impact on competition outcome between Chlorella vulgaris Beijerinck, 1890 and Chlamydomonas globosa J. W. Snow, 1902. Freshwater green algae, Chlorella, have heavy cell walls and their size usually exceeds the lower limits of hmb size of Ceriodaphnia. According to the optimal foraging theory, it is speculated that Ceriodaphnia would graze on the more exposed and relatively larger Chlamydomonas rather than on Chlorella, and this process would lead to smallsized Chlorella becoming a superior competitor in the presence of Ceriodaphnia. This work used Ceriodaphnia, Chlamydomonas globosa and Chlorella vulgaris to test this hypothesis. The grazing experiment showed that Ceriodaphnia preferred Chi. globosa to Ch. vulgaris, regardless of the concentration and relative abundance of these algae. The decrease in relative abundance of highquality Chlamydomonas in Chlamydomonas-Chlorella assemblages did not diminish the grazing efficiency of Ceriodaphnia on this algal species, but increased the selectivity of small-sized cells of Chlorella. However, when the concentration of Chlamydomonas was extremely high, the grazing of Ceriodaphnia on Chlamydomonas decreased. In competition experiments, it was observed that the presence of Chlamydomonas restrained the growth potential of Chlorella; however, the introduction of Ceriodaphnia into the competing environment weakened this influence and to some extent enhanced the growth ability of Chlorella. The different densities of Ceriodaphnia had an obvious influence on the competition outcome between Chlamydomonas and Chlorella. RÉSUMÉCette étude a testé la sélection de la nourriture par le cladocère Ceriodaphnia quadrangula (O. F. Müller, 1785) et son impact sur les résultats de la compétition entre Chlorella vulgaris Beijerinck, 1890 et Chlamydomonas globosa J. W. Snow, 1902. Les algues vertes d'eau douce Chlorella, ont des parois cellulaires épaisses et leur taille dépasse généralement la taille limite inférieure des appendices de Ceriodaphnia. Selon la "théorie de ravitaillement optimal" ["optimal foraging theory"], il est admis que Ceriodaphnia devrait brouter sur les Chlamydomonas plus exposés et relativement plus grands que sur les Chlorella, et que ce processus devrait conduire les Chlorella de taille plus petite ')

Seasonal variations in length of the copepods in Keban Dam Lake were compared and the relative influence of temperature, chlorophyll concentration, salinity, and total hardness examined. Temperature seems to be the primary factor influencing copepod body length in the Keban Dam Lake, but the various species differ markedly in their response. Calanoid copepods (Arctodiaptomus osmanus and Acanthodiaptomus denticornis) showed a more definite trend of size variation with temperature than the cyclopoid copepod, Cyclops vicinus. Differences in metabolic rate, longevity, and specialization of calanoid and cyclopoid copepods could explain their different responses to temperature. RÉSUMÉLes variations saisonnières de taille des copépodes du lac de barrage de Keban ont été comparées et l'influence relative de la température, de la concentration en chlorophylle, de la salinité et de la dureté totale a été examinée. La température semble être le premier facteur influençant la longueur du corps des copépodes dans le lac de Keban, mais les différentes espèces varient dans leur réponse de façon marquée. Les copépodes calanoïdes (Arctodiaptomus osmanus et Acanthodiaptomus denticornis) ont montré une tendance plus marquée de la variation de taille en fonction de la température que le copépode cyclopoïde Cyclops vicinus. Des différences dans les taux de métabolisme, la longévité et la spécialisation des copépodes calanoïdes et cyclopoïdes pourraient expliquer leurs réponses différentes à la température.