Trophic relationships in the Changjiang River estuarine salt marshes: preliminary investigation from δ¹³C and δ¹⁵N analysis

To obtain information on food web structure in salt marshes of the Changjiang (Yangtze) River Estuary, the δ¹³C and δ¹⁵N values of primary producers and consumers were determined. The mean δ¹³C values of 31 dominant consumers ranged from -23.13‰ to -14.37‰. Except for several species (Eriocheir sinensis, Sinonovacula constricta and Potamocorbula ustulata), consumers had intermediate δ¹³C values between those of benthic microalgae and Spartina alterniflora. The mean δ¹⁵N values of 31 dominant consumers varied between 6.87‰ and 13.33‰, which indicate three trophic levels in salt marshes of the Changjiang River Estuary. A total of 18 macroinvertebrates species and four fish species represented primary consumers with trophic levels ranging from 2.0 to 2.7. Secondary consumers included two macroinvertebrates and seven fishes with trophic levels varying between 3.0 and 3.9. The consumers were divided into three trophic guilds, i.e., detritivorous/algae feeders, omnivores and carnivores. The detrital food chain was the main energy flow pathway in the salt marsh food web of the Changjiang River Estuary, and the marsh vascular plants were at least as equally important as microphytobenthos for secondary production. The important trophic function of the salt marsh habitats in the estuary is revealed.