Original paper

Ontogenetic changes in the trophic position of a freshwater Unionidae mussel

Yasuno, Natsuru; Shindo, Kentaro; Takagi, Yuya; Kanaya, Gen; Shikano, Shuichi; Fujimoto, Yasufumi; Shimada, Tetsuo; Kikuchi, Eisuke


Freshwater mussels have often been used as indicators of a trophic baseline (i.e., primary consumers) in the food web. To assess the utility of a large filter-feeding mussel, Cristaria plicata, as an isotopic indicator, we compared the carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of the mussel with those of its potential food sources, particulate organic matter (POM) and sediment organic matter (SOM). The δ13C values of large mussels (shell length > 140 mm, –31 ‰ to –29.2 ‰) were similar to those of POM (–30.2 ‰) rather than those of SOM (–27.6 ‰), indicating that mussel carbon was derived mainly from POM (mainly phytoplankton). In contrast, the mussels exhibited 6.3 ‰ to 9.0 ‰ higher δ15N values than did POM. Assuming a previously reported trophic enrichment factor (+3.4 ‰), the trophic level estimate of the mussel ranged from 2.9 to 3.6, indicating that they functioned as secondary rather than primary consumers. Our results also revealed positive correlations between shell lengths and δ15N values, suggesting that the mussels changed their trophic position from primary consumer (shell length 140 mm) with growth. A significant inter-annual dif- ference was found in the y-intercepts of the regression lines between shell length and δ15N, indicating that mussels can reflect inter-annual changes in the isotopic baseline (i.e., primary producers).


cristaria plicatatrophic levelzooplanktonδ13cδ15n