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首页> 外文期刊>Aquatic sciences >Utilization of basal resources in a forested headwater stream: a combined stable isotope and fatty acid approach
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Utilization of basal resources in a forested headwater stream: a combined stable isotope and fatty acid approach

机译：Utilization of basal resources in a forested headwater stream: a combined stable isotope and fatty acid approach

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In mountainous areas, forest headwater streams are characterized by a predominantly heterotrophic functioning resulting from massive seasonal allochthonous litter input. However, autochthonous primary production can contribute significantly to energy fluxes when canopies are open and in exposed stream reaches. Understanding whether this contribution tends to be limited to a supplementary supply of essential nutrients such as polyunsaturated fatty acids (PUFAs) or whether it supports the whole food web is a central theme in freshwater ecology. We carried out seasonal monitoring in a forest stream near its main source during the period of increasing secondary production (April-November). Combining stable isotopes (~(13)C-~(15)N) and fatty acid analyses, we found that autochthonous primary production constituted the leading resource for five specific macroinvertebrate taxa in spring and summer. The leaf litter deposits were monospecific (Fagus sylvatica) and proved to be poorly used. In contrast, fine benthic organic matter (FBOM), mostly produced from leaf litter degradation, provided a significant source of quality food used by primary consumers (Gammarus pulex, Ecdyonorus sp. and Leuctra spp.). Our data analysis confirms that epilithic and epixylic biofilms (associated with FBOM) were the source of the essential PUFAs (20∶4ω6 and 20∶5ω3), assimilated by the macroinvertebrate studied. Furthermore, at some period, the predatory taxa (Isoperla ambigua and Rhyacophila spp.) also derived 20∶4ω6 and 20∶5ω3 from the direct ingestion of microalgae. Despite their formal functional feeding group, all the macroinvertebrate taxa tended to be opportunistic omnivores that relied on all available resources.

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