Tidal marshes as energy sources for commercially important nektonic organisms: stable isotope analysis

Tidal marshes provide nursery habitats for many commercial nektonic species; thus, determining trophic linkages between tidal marshes and aquatic consumers is important for sustaining fishery production in estuarine ecosystems. We examined stable isotopes (δ13C, δ15N) in 4 commercial nekton species (Chelon haematocheilus, Synechogobius ommaturus, Lateolabrax maculatus and Exopalaemon carinicauda) in the tidal marshes of the Yangtze River estuary, China. We estimated the frequency and range of potential contribution (0 to 100%) from different food sources (benthic microalgae, suspended particulate organic matter, the invasive C4 plant Spartina alterniflora and native C3 plants Phragmites australis and Scirpus mariqueter) to the nektonic consumers, and then pooled the contributions for primary producers with similar isotope values (giving 3 groups: microalgae, invasive C4 plant and native C3 plants). Marsh vascular plants and microalgae were at the base of the food web supporting these nektonic species. For C. haematocheilus and S. ommaturus, vascular plants constituted a larger fraction of their carbon source than microalgae. S. alterniflora contributed more than 50% of their total organic carbon and was more important than the native C3 plants. For L. maculatus and E. carinicauda, intermediate δ13C values precluded definitive assignment of a major carbon source. We have shown that tidal marshes provide important food sources for some dominant estuarine nektonic species, and that the exotic plant S. alterniflora has been incorporated into aquatic food webs of the Yangtze River estuary.