Spatial and seasonal variability of the carbon isotopic signature of Daphnia and their ephippia in four French lakes: Implications for the study of carbon transfers in lake food webs - Archive ouverte HAL Access content directly
Journal Articles Freshwater Biology Year : 2022

Spatial and seasonal variability of the carbon isotopic signature of Daphnia and their ephippia in four French lakes: Implications for the study of carbon transfers in lake food webs

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Abstract

Carbon isotope analysis (delta C-13) of Daphnia resting-eggs (ephippia) in sedimentary records can be used to reconstruct past carbon transfers in pelagic food webs in lakes. However, there may be seasonal variability of cladoceran delta C-13 and ephippia production that could affect their use as palaeoecological indicators of pelagic carbon transfers. This is particularly likely in stratified lakes where availability of different pelagic carbon sources is seasonal. In addition, there are currently no studies on spatial variability of ephippia delta C-13 in deep areas of lakes and its implications for sampling strategies in paleolimnological studies. Four French lakes were sampled for over a year to evaluate seasonal variation of the carbon sources consumed by Daphnia using analyses of the Daphnia carbon isotope signature (delta C-13(Daphnia)) and suspended organic matter signature (delta C-13(seston)). Daphnia ephippia were also collected from surface sediments at maximum depth in the four lakes. Ephippia signatures (delta C-13(ephippia)) were compared to the delta C-13(Daphnia) to evaluate ephippia production periods and the implications for the use of delta C-13(ephippia) in trophic functioning studies. In addition, spatial variability of delta C-13(Daphnia) among the four lakes and the variability of delta C-13(ephippia) in the deep area of one lake were assessed to determine the relevance of a single sampling point in the context of paleolimnological studies. A similar pattern was observed in all four lakes: delta C-13(Daphnia) was close to delta C-13(seston) during the summer stratification period, but delta C-13(Daphnia) became much lower than delta C-13(seston) after the autumnal turnover. Ephippia seem to be produced either during the summer stratification period or after autumnal turnover depending on the lake. No spatial variability was observed among the sampling points in delta C-13(Daphnia) in the four lakes, and delta C-13(ephippia) seems to be spatially randomly distributed in the deep zone of the studied lake. In the four lakes, summer delta C-13(Daphnia) values were never below -40 parts per thousand, reflecting mainly the consumption of phytoplankton, which in turn uses varying amounts of CO2 from respiration (depending on the lake). After autumnal turnover, the delta C-13(Daphnia) values reached values far below -40 parts per thousand, reflecting the transfer of a non-negligible part of C-CH4 for three of the lakes. Seasonal stratification and turnover mechanisms seem to influence the availability of carbon sources in the pelagic compartment of the four lakes. This study shows that the timing of ephippia production affects the information provided by delta C-13(ephippia) due to seasonal differences in the mechanisms (stratification, autumnal turnover) that determine which carbon sources are available in the pelagic compartment. Therefore, using delta C-13(ephippia) to study past pelagic transfers of carbon in stratified lakes may entail uncertainty if used alone and requires multi-proxy studies. Finally, delta C-13(ephippia) appear to be homogeneously distributed in the deepest area of a medium-sized, single basin. A single core retrieved from the deepest part of the lake should therefore provide a representative sample of the ephippia produced in a lake.
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hal-03711150 , version 1 (01-07-2022)

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Attribution - CC BY 4.0

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Valentin Essert, Hélène Masclaux, Valérie Verneaux, Émilie Lyautey, David Etienne, et al.. Spatial and seasonal variability of the carbon isotopic signature of Daphnia and their ephippia in four French lakes: Implications for the study of carbon transfers in lake food webs. Freshwater Biology, 2022, ⟨10.1111/fwb.13952⟩. ⟨hal-03711150⟩
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