Utilization of exotic Spartina alterniflora by fish community in the mangrove ecosystem of Zhangjiang Estuary: evidence from stable isotope analyses

The cordgrass Spartina alterniflora has invaded mangrove-dominated habitats in China during the last few decades. However, the ecological effect of the S. alterniflora on the mangrove fish community is poorly understood. In order to assess the relative nutritional contributions of native autotrophs (benthic microalgae: BMA, particulate organic matter: POM, C-3 native mangrove Aegiceras corniculatum, Avicennia marina and Kandelia obovata) and C-4 exotic S. alterniflora, we examined the stable carbon and nitrogen isotope values of six common fish species (Osteomugil ophuyseni, Coilia grayii, Parachaeturichthys polynern, Sparus latus, Lateolabrax japonicas and Ophichthus apicalis) in the tidal creek of Zhangjiang Estuary. Results of the MixSIR model suggested that exotic S. alterniflora combined with BMA constituted major food sources of the fish community. S. alterniflora had a higher median contribution than all the other food sources to all fish species except for P. polynerna and S. latus, which derived their major food sources from BMA. These results indicated that the invasive cordgrass has been incorporated into the local aquatic food web through providing important nutrient source for fish species in the mangrove ecosystem of Zhangjiang Estuary.