Pierre Quévreux, Kejun Zou, Sébastien Barot, Élisa Thébault, Emma Rochelle-Newall, Ludwig Jardillier, Éric Edeline, Simon Agostini, Jacques Mériguet, Sarah Fiorini, Gérard Lacroix
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Thus, bottom-up or top-down effects on one food web can have major cascading effects on the other one.</li>\n \n \n <li>In our freshwater mesocosm experiment, we tested cascading bottom-up effects targeting the green food web through sunlight filtering and the brown food web through organic carbon addition; cascading top-down effects mediated by fish presence.</li>\n \n \n <li>Our main finding is a positive effect of fish on phytoplankton density in mesocosms where daylight was reduced. Fish also had a positive effect on the brown food web with increased abundances of heterotrophic prokaryotes and microbial eukaryotes. However, they had no significant effect on zooplankton biomass. We did not observe any cascading effect of light treatment on the brown food web and of organic carbon treatment on the green food web. Our organic carbon treatment had nearly no effect on the brown food web.</li>\n \n \n <li>The most likely explanation for the observed fish × light interaction is a bottom-up effect mediated by nutrient cycling embodied by the increased sediment production and DOC accumulation in the presence of fish. The lack of effect of our organic carbon treatment may be due to the moderate quantity of added carbon and of the low bioavailability of some of the added molecules.</li>\n \n \n <li>Our experiment suggests that fish can strongly stimulate phytoplankton through bottom-up effects due to nutrient cycling, and not only through the classic trophic cascade due to the top-down control on large herbivorous zooplankton.</li>\n </ol>\n \n </div>","PeriodicalId":12365,"journal":{"name":"Freshwater Biology","volume":"70 8","pages":""},"PeriodicalIF":2.7000,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Combined Effects of Fish, Light and Allochthonous Dissolved Organic Carbon on Interactions Between Green and Brown Food Webs: An Aquatic Mesocosm Experiment\",\"authors\":\"Pierre Quévreux, Kejun Zou, Sébastien Barot, Élisa Thébault, Emma Rochelle-Newall, Ludwig Jardillier, Éric Edeline, Simon Agostini, Jacques Mériguet, Sarah Fiorini, Gérard Lacroix\",\"doi\":\"10.1111/fwb.70081\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div>\\n \\n <p>\\n \\n </p><ol>\\n \\n \\n <li>The classical concepts of top-down and bottom-up cascading effects in ecosystems are challenged by the interactions between green and brown food webs. The green food web relies on photosynthesis and the brown food web relies on the mineralisation of dead organic matter. Mutualistic interactions between these two food webs are crucial for ecosystem functioning because a major fraction of organic carbon is produced by the green food web, while mineral nutrients are mainly recycled through the brown one. However, green and brown food webs can compete for mineral nutrients if decomposers are nutrient limited. Thus, bottom-up or top-down effects on one food web can have major cascading effects on the other one.</li>\\n \\n \\n <li>In our freshwater mesocosm experiment, we tested cascading bottom-up effects targeting the green food web through sunlight filtering and the brown food web through organic carbon addition; cascading top-down effects mediated by fish presence.</li>\\n \\n \\n <li>Our main finding is a positive effect of fish on phytoplankton density in mesocosms where daylight was reduced. 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Combined Effects of Fish, Light and Allochthonous Dissolved Organic Carbon on Interactions Between Green and Brown Food Webs: An Aquatic Mesocosm Experiment
The classical concepts of top-down and bottom-up cascading effects in ecosystems are challenged by the interactions between green and brown food webs. The green food web relies on photosynthesis and the brown food web relies on the mineralisation of dead organic matter. Mutualistic interactions between these two food webs are crucial for ecosystem functioning because a major fraction of organic carbon is produced by the green food web, while mineral nutrients are mainly recycled through the brown one. However, green and brown food webs can compete for mineral nutrients if decomposers are nutrient limited. Thus, bottom-up or top-down effects on one food web can have major cascading effects on the other one.
In our freshwater mesocosm experiment, we tested cascading bottom-up effects targeting the green food web through sunlight filtering and the brown food web through organic carbon addition; cascading top-down effects mediated by fish presence.
Our main finding is a positive effect of fish on phytoplankton density in mesocosms where daylight was reduced. Fish also had a positive effect on the brown food web with increased abundances of heterotrophic prokaryotes and microbial eukaryotes. However, they had no significant effect on zooplankton biomass. We did not observe any cascading effect of light treatment on the brown food web and of organic carbon treatment on the green food web. Our organic carbon treatment had nearly no effect on the brown food web.
The most likely explanation for the observed fish × light interaction is a bottom-up effect mediated by nutrient cycling embodied by the increased sediment production and DOC accumulation in the presence of fish. The lack of effect of our organic carbon treatment may be due to the moderate quantity of added carbon and of the low bioavailability of some of the added molecules.
Our experiment suggests that fish can strongly stimulate phytoplankton through bottom-up effects due to nutrient cycling, and not only through the classic trophic cascade due to the top-down control on large herbivorous zooplankton.
期刊介绍:
Freshwater Biology publishes papers on all aspects of the ecology of inland waters, including rivers and lakes, ground waters, flood plains and other freshwater wetlands. We include studies of micro-organisms, algae, macrophytes, invertebrates, fish and other vertebrates, as well as those concerning whole systems and related physical and chemical aspects of the environment, provided that they have clear biological relevance.
Studies may focus at any level in the ecological hierarchy from physiological ecology and animal behaviour, through population dynamics and evolutionary genetics, to community interactions, biogeography and ecosystem functioning. They may also be at any scale: from microhabitat to landscape, and continental to global. Preference is given to research, whether meta-analytical, experimental, theoretical or descriptive, highlighting causal (ecological) mechanisms from which clearly stated hypotheses are derived. Manuscripts with an experimental or conceptual flavour are particularly welcome, as are those or which integrate laboratory and field work, and studies from less well researched areas of the world. Priority is given to submissions that are likely to interest a wide range of readers.
We encourage submission of papers well grounded in ecological theory that deal with issues related to the conservation and management of inland waters. Papers interpreting fundamental research in a way that makes clear its applied, strategic or socio-economic relevance are also welcome.
Review articles (FRESHWATER BIOLOGY REVIEWS) and discussion papers (OPINION) are also invited: these enable authors to publish high-quality material outside the constraints of standard research papers.