Length-specific carbon content of theDaphnia population in a large subalpine lake, Lago Maggiore (Northern Italy): The importance of seasonality |
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| Authors: | Marina Manca Patrizia Comoli Teresa Spagnuolo |
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| Institution: | (1) C.N.R. Istituto Italiano di Idrobiologia Largo Tonolli 50/52, I-28048 Pallanza, Italy |
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| Abstract: | We compared three methods for calculating the standing stock biomass ofDaphnia hyalina galeata population in Lago Maggiore during a single year. We applied body length/carbon regression equations (LCR) obtained under
controlled laboratory conditions and directly from field data on carbon and body length to field data on length-specific abundance.
Laboratory-derived equations satisfactorily described our field estimates of length-specific carbon content in spring. As
the length-standardized carbon content decreased exponentially along the season, we included time of the year as an auxiliary
variable, and tested whether it affected slope, intercept or both. The decrease had no effect on slope but reduced the intercept
of the LCR. We also calculated biomass, using a single mean value from the literature. By comparing the results with those
obtained by simple conversion of individuals number into carbon we might discriminate between the effect of changes in the
size frequency distribution of the population and the decrease with time of the length-standardized carbon content. Although
we tested the different models for non-ovigerous females, the results did not change when we included also data on females
with eggs in the first three developmental stages, whereas they changed substantially when we included females with embryos.
We formulate two hypotheses to explain this result and discuss possible implications for the calculation of the standing stock
biomass ofDaphnia population. |
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| Keywords: | Carbon inDaphnia |
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