Physiological responses of Daphnia catawba, Coker to manipulations of naturally occurring seston in in situ enclosures

Page, Lewis Kenneth (1987) Physiological responses of Daphnia catawba, Coker to manipulations of naturally occurring seston in in situ enclosures. Masters thesis, Memorial University of Newfoundland.

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Abstract

Filtering rate, length-specific weight, and fecundity were used as measures of short, medium and long-term responses of individual Daphnia catawba to manipulation of the natural food supply and to seasonal fluctuations in water temperature. Natural lake seston concentration was manipulated to encompass a realistic range of food concentrations in in situ enclosures and six, four or eight day experiments were conducted over a two month period to take advantage of seasonal variability in lake water temperature. Based on prior laboratory studies, both filtering rate and length-specific weight were expected to respond to changes in food supply and water temperature and a threshold food concentration was expected above which weight gain would occur. The results of this study are in general agreement with predictions from earlier laboratory studies. The general seston components (chl a, POC, PON) were not significantly correlated with filtering rate and net weight change in Daphnia catawba. Only the plankton biomass component and water temperature variables explained significant levels of variation in filtering rate and net weight change. Filtering rates were weakly, negatively correlated with an edible (5-10 μm) plankton biomass and positively correlated with an edible (5-10 μm) plankton biomass component. Multiple linear regression analysis indicated that these variables explained 14, 20 and 13% of the variance in filtering rate of small, medium and large animals respectively. Net weight change; calculated as the difference between the final and initial dry body weights, was found to be significantly positively correlated with the smallest plankton component (<2 μm) and significantly negatively correlated with water temperature, with multiple regression models explaining 35, 37 and 58% of the variance in net weight change for small, medium and large animals respectively. Net weight change in large animals was also significantly negatively correlated with initial animal weight (r==-.782). Fecundity responses to seston manipulation and water temperature fluctuation were minimal; adult females appeared to allocate excess energy to growth rather than reproduction.

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