Declines in the tuber-feeding waterbird guild at Shengjin Lake National Nature Reserve, China - a barometer of submerged macrophyte collapse

1. The Yangtze floodplain is globally unique for its extensive ephemeral wetlands, recharged by summer monsoon precipitation. The annual cycle of inundation and water table recession favours submerged macrophytes, including Vallisneria that overwinters in desiccated substrates as tubers, which provide high-energy winter food for tuber-feeding waterbirds that were formerly abundant in the region. 2. Large declines among the tuber-feeding waterbirds swan goose Anser cygnoides (L.), tundra swan Cygnus columbianus (Ord) and hooded crane Grus monacha Temminck between 2004/2005 and 2009/2010 at Shengjin Lake, Anhui Province, suggest that major changes in food availability have occurred there. 3. Based on observations of feeding behaviour and energy budgets of these species, it was calculated that at least 5.0 and 8.9 km(2) of Vallisneria beds in 2004 and 2005, respectively, would be needed to support observed numbers of these species, compared with less than 1.5 km(2) found in 2009 and 2010. 4. An incomplete macrophyte survey in summer 2000 located at least 7.7 km(2) of Vallisneria beds in the Upper Lake, where none was present during resurveys in 2008 and 2009. Declines in tuber-feeding waterbirds at Shengjin Lake coincide with the disappearance of their submerged macrophyte food plants, possibly as a result of eutrophication since the mid-2000s. 5. Widespread declines and concentration of tuber-eating wintering waterbirds at other sites elsewhere in the Yangtze floodplain may also reflect the local collapse of submerged macrophytes and of ecosystem services that these wetlands provide to the human communities. Copyright (C) 2010 John Wiley & Sons, Ltd.