Abstract
Using carbon and nitrogen stable isotope analysis, we characterised food web properties of the deep subtropical Fei-Tsui Reservoir (FTR), which was recently altered from a lotic to a lentic system after dam construction. In the littoral zone, zoobenthos showed strong reliance (83.9%) on benthic algal production. Zoobenthos were never found in the profundal zone because of anoxia. Zooplankton depleted 13C more than that of particulate organic matter as their putative food source, suggesting a contribution of methane-derived carbon to pelagic food webs. Excluding juveniles, non-native and fluvial species, adult fish showed strong reliance (on average 80.9%) on benthic production, weakly coupled with pelagic food webs. These results contrast low benthic production reliance (on average 27.4%) for a fish community in Lake Biwa, which is also classified as a subtropical lake. Both lakes are characterised by deep pelagic waters but quite different in their geological ages, suggesting that the aquatic communities in the FTR have fluvial origins, and their lacustrine history was too short for them to adapt to newly emerged deep pelagic habitat. Our isotope data are useful as a reference of newly established lentic food webs to monitor ongoing ecological and evolutionary dynamics as a result of anthropogenic disturbances.
Highlights
Dams and reservoirs have been constructed to meet accelerated demands for water and energy resources as populations experience explosive growth and climate change worldwide (Nilsson et al, 2005)
Trophic position cannot be estimated for meso- and macro-zooplankton because they depleted 13C substantially more than particulate organic matter (POM), which is their putative food source (Fig. 2; Table 2)
This suggests that the former TLs were higher than the latter by around one their absolute values could not be calculated because of large deviations from the isotopic range of their putative food sources, POM and epilithic organic matter (EOM)
Summary
Dams and reservoirs have been constructed to meet accelerated demands for water and energy resources as populations experience explosive growth and climate change worldwide (Nilsson et al, 2005). The stable isotopic approach is the preferred method for studying aquatic food webs, in which carbon (d13C) and nitrogen (d15N) isotope ratios, for aquatic species, are used to distinguish primary trophic pathways, for example, pelagic versus littoral pathways (France, 1995a, b) or aquatic versus terrestrial pathways (Peterson & Fry, 1987; Finlay, 2001). For fish, their isotopic signatures provide useful information in estimating the relative importance of trophic energy flows in lake ecosystems. As such, limited information is available on original conditions before the disturbance (but see Okuda et al, 2012; Vander Zanden et al, 2003)
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