Developmental Responses of Juvenile Daphnia rosea to Experimental Alteration of Temperature and Natural Seston Concentration

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Abstract
A need for accurate estimates of juvenile development rates of Daphnia rosea from oligotrophic lakes prompted this investigation into the combined effects of temperature and natural seston concentrations on growth of neonates. Significant effects of seston concentration and temperature and especially their interaction were detected upon survival, number of prereproductive instars, growth increment per instar, and duration of development. Low summertime seston concentrations that were sufficient for good survival and growth at a low rearing temperature (12 °C) generally produced high mortality, slow development, and reduced biomass increments at higher temperature (21 °C). Further, poor growth and survival under low seston – high temperature conditions were exaggerated in August compared with May, suggesting possible seasonal changes in natural seston quality and/or juvenile daphnid physiology. In contrast, higher food levels typical of springtime conditions produced excellent survival and growth regardless of the test temperature employed or season examined. Food limitation of daphnid development was thus dependent upon both temperature and food concentration within the range of conditions commonly observed in oligotrophic lakes. Extrapolation of development rates measured under only a limited range of food–temperature conditions or taken from literature values should be done cautiously.Key words: Daphnia, development, juvenile, seston, food, temperature, growth, survival, Cladocera, oligotrophic