Incorporation of Exotic Spartina alterniflora into Diet of Deposit-Feeding Snails in the Yangtze River Estuary Salt Marsh: Stable Isotope and Fatty Acid Analyses

The response of deposit-feeding animals to plant invasions is still unclear, because their food sources are often difficult to identify. We examined the effect of the exotic plant species, Spartina alterniflora, on the food source composition of two dominant snail species, Assiminea latericea and Cerithidea largillierti, in the Yangtze River estuary salt marsh using a combination of stable isotope and fatty acid analyses. We collected the snails and their potential food materials (sediment organic matter, particulate organic matter, and plant material) in S. alterniflora and native plant Phragmites australis marshes and then determined the composition of food sources of snails based on fatty acid markers and stable isotope composition. Our results indicated that A. latericea and C. largillierti are deposit feeders grazing on sedimentary particles originating from diatoms, bacteria, and vascular plants. Invasive S. alterniflora did not result in a change in the relative contribution of microalgae, bacteria, and vascular plants to the food source of the snails. Spartina alterniflora was confirmed to be assimilated by both snail species. The higher assimilation of S. alterniflora by A. latericea compared with C. largillierti is probably related to the greater ability of A. latericea to assimilate plant materials from detritus, as evidenced by fatty acid composition. Overall, S. alterniflora can be incorporated into the food web of the estuarine salt marsh by the dominant snail species with generalist-feeding habits.