Food-web responses to restoration of channel heterogeneity in boreal streams

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Abstract:

We assessed the biomass and stable-isotope composition (13C and 15N) of consumers (aquatic insects and fish (Cottus gobio)) and potential food sources (detritus, biofilm, seston, algae, and mosses) in channelized and restored streams in Sweden, assessing the hypotheses that restoration enhances detritus storage and detritus-based secondary production. Restored sites stored more detritus than channelized sites, with differences (+5.4% on average) prominent in margins, i.e., the channel area within 1.4 m from the banks. The biomass of other resources was similar between restored and channelized sites. Most common aquatic insects, including several putative detritivores, showed 13C values indicating reliance on aquatic (probably algal) carbon sources. The insectivorous fish Cottus gobio, on the contrary, appeared to be more dependent on terrestrial (detrital) carbon sources. The biomass and mean 13C values of the consumers were similar between restored and channelized sites, suggesting that restoration did not increase net secondary production or the fraction of secondary production based on detritus. We concluded that the increase in detritus storage at restored sites was either insufficient to enhance detritus-based production or the consumers were not limited by the availability of detritus.

Nous évaluons la biomasse et la composition en isotopes stables (13C et 15N) des consommateurs (insectes aquatiques et poissons (Cottus gobio)) et de leurs sources potentielles de nourriture (détritus, biofilm, seston, algues et mousses) dans des cours d'eau canalisés et restaurés en Suède; nous vérifion les hypothèses selon lesquelles la restauration favorise le stockage du détritus et la production secondaire à base de détritus. Les sites restaurés accumulent plus de détritus que les sites canalisés et les différences (+5,4 % en moyenne) sont plus importantes près des bords, c'est-à-dire dans le chenal dans le premier 1,4 m de la rive. La biomasse des autres ressources est semblable dans les sites canalisés et restaurés. La plupart des insectes aquatiques, y compris plusieurs détritivores présumés, ont des valeurs de 13C qui indiquent une dépendance vis-à-vis des sources aquatiques de carbone (probablement les algues). Le poisson insectivore Cottus gobio, au contraire, semble être plus dépendant des sources terrestres de carbone (le détritus). La biomasse et les valeurs moyennes de 13C des consommateurs sont semblables dans les sites canalisés et restaurés, ce qui semble montrer que la restauration n'augmente pas la production secondaire nette, ni la fraction de la production secondaire à base de détritus. En conclusion, l'augmentation du stockage de détritus aux sites restaurés est insuffisante pour augmenter la production secondaire à base de détritus, ou alors les consommateurs ne sont pas limités par la disponibilité du détritus.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2006

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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