Abstract
Benthic bivalves are important links between primary production and consumers, and are essential intermediates in the flow of energy through estuarine systems. However, information on the diet of filter feeding bivalves in estuarine ecosystems is uncertain, as estuarine waters contain particulate matter from a range of sources and as bivalves are opportunistic feeders. We surveyed bivalves at different distances from the creek mouth at the Yangtze estuarine marsh in winter and summer, and analyzed trophic dynamics using stable isotope (SI) and fatty acid (FA) techniques. Different bivalve species had different spatial distributions in the estuary. Glauconome chinensis mainly occurred in marshes near the creek mouth, while Sinonovacula constricta preferred the creek. Differences were found in the diets of different species. S. constricta consumed more diatoms and bacteria than G. chinensis, while G. chinensis assimilated more macrophyte material. FA markers showed that plants contributed the most (38.86 ± 4.25%) to particular organic matter (POM) in summer, while diatoms contributed the most (12.68 ± 1.17%) during winter. Diatoms made the largest contribution to the diet of S. constricta in both summer (24.73 ± 0.44%) and winter (25.51 ± 0.59%), and plants contributed no more than 4%. This inconsistency indicates seasonal changes in food availability and the active feeding habits of the bivalve. Similar FA profiles for S. constricta indicated that the bivalve had a similar diet composition at different sites, while different δ13C results suggested the diet was derived from different carbon sources (C4 plant Spartina alterniflora and C3 plant Phragmites australis and Scirpus mariqueter) at different sites. Species-specific and temporal and/or spatial variability in bivalve feeding may affect their ecological functions in intertidal marshes, which should be considered in the study of food webs and material flows in estuarine ecosystems.
Highlights
Marshes with emergent vegetation are a common feature of most estuaries and coastal plains all over the world
Glauconome chinensis mainly occurred in marsh habitats, while S. constricta preferred creek habitats (Fig 2)
Based on distribution patterns and food sources, our study indicates that the different bivalve species examined in this study, had separate ecological niches in the Yangtze estuarine marshes
Summary
Marshes with emergent vegetation are a common feature of most estuaries and coastal plains all over the world. The structure of the estuarine food web is complicated by seasonal changes resulting from freshwater discharge shifts, and by the spatial mosaic within estuaries created by different vegetation types and tidal amplitudes [3,4,5,6]. Benthic bivalves are important links between primary production and high level trophic consumers such as fishes, crabs and birds, and are key intermediates in the energy flow of estuarine systems. They obtain food by filtering out particulate material, and exert grazing control over phytoplankton production [7, 8]. Despite an increasing interest in food-web dynamics, little is known about the spatial and temporal changes of trophic pathways supporting bivalves in estuarine salt marshes
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