Dissolved Organic Carbon Reduces Habitat Coupling by Top Predators in Lake Ecosystems
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Increasing input of terrestrial dissolved organic carbon (DOC) has been identified as a widespread environmental phenomenon in many aquatic ecosystems. Terrestrial DOC influences basal trophic levels: it can subsidize pelagic bacterial production and impede benthic primary production via light attenuation. However, little is known about the impacts of elevated DOC concentrations on higher trophic levels, especially on top consumers. Here, we used Eurasian perch (Perca fluviatilis) to investigate the effects of increasing DOC concentrations on top predator populations. We applied stable isotope analysis and geometric morphometrics to estimate long-term resource and habitat utilization of perch. Habitat coupling, the ability to exploit littoral and pelagic resources, strongly decreased with increasing DOC concentrations due to a shift toward feeding predominantly on pelagic resources. Simultaneously, resource use and body morphology became increasingly alike for littoral and pelagic perch populations with increasing DOC, suggesting more intense competition in lakes with high DOC. Eye size of perch increased with increasing DOC concentrations, likely as a result of deteriorating visual conditions, suggesting a sensory response to environmental change. Increasing input of DOC to aquatic ecosystems is a common result of environmental change and might affect top predator populations in multiple and complex ways.
Keywordsallochthony brownification food web coupling visibility foraging climate change
We thank J Malmberg, E Geibrink, M Puffer, M Möst, and A Klaussén for help in the field and in the lab and the two anonymous reviewers for their highly valuable comments on a previous version of the manuscript. This study was financed by grants from the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (FORMAS) to PB and PE, the Swedish Research Council (VR) to PE and RS, the Uppsala Graduate School to PEH, and the Malmén´s Foundation to PB and PEH.
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