Blinded by the light? Nearshore energy pathway coupling and relative predator biomass increase with reduced water transparency across lakes
Habitat coupling is a concept that refers to consumer integration of resources derived from different habitats. This coupling unites fundamental food web pathways (e.g., cross-habitat trophic linkages) that mediate key ecological processes such as biomass flows, nutrient cycling, and stability. We consider the influence of water transparency, an important environmental driver in aquatic ecosystems, on habitat coupling by a light-sensitive predator, walleye (Sander vitreus), and its prey in 33 Canadian lakes. Our large-scale, across-lake study shows that the contribution of nearshore carbon (δ13C) relative to offshore carbon (δ13C) to walleye is higher in less transparent lakes. To a lesser degree, the contribution of nearshore carbon increased with a greater proportion of prey in nearshore compared to offshore habitats. Interestingly, water transparency and habitat coupling predict among-lake variation in walleye relative biomass. These findings support the idea that predator responses to changing conditions (e.g., water transparency) can fundamentally alter carbon pathways, and predator biomass, in aquatic ecosystems. Identifying environmental factors that influence habitat coupling is an important step toward understanding spatial food web structure in a changing world.
KeywordsFood webs Trophic interactions Environmental change Stable isotopes Water clarity Sander vitreus
We thank biologists and technical staff at the OMNRF Broad-Scale Monitoring Program for assistance with sample collection. S. Sandstrom, K. Armstrong, and J. Wright were particularly helpful with logistics and offered sampling advice. We also acknowledge the efforts of A. Oulimette and R. Mixon (University of New Hampshire Stable Isotope Laboratory). Beren W. Robinson provided helpful comments on an early draft of the manuscript. We also acknowledge Leon Barmuta and anonymous reviewers for constructive comments. Helpful discussion included K.S.M. laboratory members. TDT acknowledges useful discussion with the ‘Bass-walleye group’ a collaboration between WDNR, USGS, and the Center for Limnology UW-Madison. Research was supported by grants from the Natural Sciences and Engineering Research Council of Canada (to B.J.S. and K.S.M.) and the Climate Change Program of the OMNRF. Additional support came through a Tier 2 Canada Research Chair held by K.S.M. Partial support from CFREF to KSM.
TDT, KSM, NPL and BJS conceived and designed the study. TDT and LJ collected field data and conducted lab work. TDT, LJ, NPL and BJS organized and analyzed data. TDT wrote the initial draft of the manuscript. All authors provided editorial advice.
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