Food web properties of the recently constructed, deep subtropical Fei-Tsui Reservoir in comparison with the ancient Lake Biwa

Hydrobiologia, Jun 2017

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.

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Food web properties of the recently constructed, deep subtropical Fei-Tsui Reservoir in comparison with the ancient Lake Biwa

Hydrobiologia Food web properties of the recently constructed, deep subtropical Fei-Tsui Reservoir in comparison with the ancient Lake Biwa Handling editor: Michael Power 0 1 2 3 4 0 K. Fukumori Center for Environmental Biology and Ecosystem Studies, National Institute for Environmental Studies , Tsukuba 305-8506 , Japan 1 Y. Sakai Lake Biwa Environmental Research Institute , Otsu 520-0022 , Japan 2 N. Okuda (&) Research Institute for Humanity & Nature , Kyoto 603-8047 , Japan 3 F.-K. Shiah (&) Research Center for Environmental Changes , Academia Sinica, Taipei 115 , Taiwan 4 S.-M. Yang C. Hsieh Institute of Oceanography, National Taiwan University , Taipei 10617 , Taiwan 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. Dam construction; Production reliance; Stable isotope analysis; Trophic flow; Trophic position Introduction 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) . While dams provide high public utility, they can negatively impact river ecosystems by drastically changing waterway from lotic to lentic systems (McAllister et al., 2001) . In dammed rivers, some taxa can modify and adapt their life histories to sustain their populations; however, others that cannot adapt may go into local extinction due to loss of original habitats. At present, dam construction is considered as one of the major drivers of biodiversity loss in the freshwater ecosystems through the alteration and homogenisation of natural hydrological regimes (Poff et al., 2007) , the creation of physical barriers to migratory species (Liermann et al., 2012) , the dispersal and colonisation of non-native lentic species (Havel et al., 2005) , and the pollution and eutrophication at dam sites (Dudgeon, 2000) . Therefore, it is important to perform ecosystem assessments after dam construction for water quality management and biodiversity conservation. Stable isotope analysis (SIA) is a powerful tool to assess ecosystems, especially food web properties characterised by trophic interactions within a biological community. Food web characterisation is of ecological and social significance because trophic interactions can drive nutrient cycling and energy flows, which in turn affect ecosystem services (e.g. water quality, food supply for humanity). At present, 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) . Especially for fish, their isotopic signatures provide useful information in estimating the relative importance of trophic energy flows in lake ecosystems. Fish predators integrate a variety of trophic pathways as they couple pelagic and littoral food webs due to their high mobility and omnivory (Vander Zanden & Vadeboncoeur, 2002; Vander Zanden et al., 2011) . The stable isotopic approach can also be applied to assess food web alterations in aquatic ecosystems under human disturbances (Vander Zanden et al., 1999; Layman et al., 2007; Anderson & Cabana, 2009; Hamaoka et al., 2010) . In most cases, however, stable isotopic studies are conducted after ecosystem alterations were perceived. As such, limited information is available on original conditions before the disturbance (but see Okuda et al., 2012; Vander Zanden et al., 2003) . Newly constructed dams and reservoirs provide a good possibility to unders (...truncated)


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Noboru Okuda, Yoichiro Sakai, Kayoko Fukumori, Shao-Min Yang, Chih-hao Hsieh, Fuh-Kwo Shiah. Food web properties of the recently constructed, deep subtropical Fei-Tsui Reservoir in comparison with the ancient Lake Biwa, Hydrobiologia, 2017, pp. 199-210, Volume 802, Issue 1, DOI: 10.1007/s10750-017-3258-4