Toward using Margaritifera falcata as an indicator of base level nitrogen and carbon isotope ratios: insights from two California Coast Range rivers

Abstract

Measurements of freshwater mussel tissue are potentially very useful for determining base-level isotopic values for food web studies in aquatic environments. As long-lived, filter-feeding organisms, mussels have the potential to spatially and temporally average the isotopic baseline signal. Following from earlier studies that focused on lake environments, this study investigates the stable carbon and nitrogen isotope ratios in tissue of the river dwelling freshwater mussel, Margaritifera falcata, in two extensively studied northern California coast range rivers, the South Fork Eel and Navarro. We highlight advantages and challenges for using riverine mussel isotopes as indicators of baselines. d 13 C of primary producers is known to vary with habitat along the South Fork Eel channel, but our measurements show no such variations, demonstrating that riverine mussels do preserve a spatially averaged measure of instream derived food sources. Mean d 13 C and d 15 N are shown to be markedly different in the two rivers, reflecting differences in food sources and possibly watershed land use. We also found that d 15 N of mussel tissue increased by approximately 2& with mussel age in both rivers. This suggests it is important to consider age and size effects when estimating baseline values from mussel tissues.

Effect of the western pearlshell mussel Margaritifera falcata on Pacific lamprey Lampetra tridentata and ecosystem processes

“…riffle and pool derived algae, with relatively depleted and enriched carbon, respectively as shown by Finlay et al 1999) and/or possibly terrestrial sources. Lamprey tissue values were similar to Margaritifera tissue δ 13 C and δ 15 N values (−22.9‰, 2.6‰, respectively) reported by Howard et al (2005) during the summer period in the South Fork of the Eel River. Finlay et al (1999) report summer δ 13 C values in the South Fork of the Eel River of −17.9‰ for epilithic algae in pool habitats, −26.2‰ for epilithic algae in riffle habitats, and −27.5‰ for terrestrial detritus.…”

Brackish water foraging: isotopic landscapes and dietary reconstruction in Suisun Marsh, Central California

“…3 plots data from modern plant and animal samples amalgamated from a wide range of studies in and around Suisun Marsh, including San Francisco Bay and the California Delta (data assembled from Bartelink, 2006;Canuel et al, 1995;Cloern et al, 2002;Goldberg, 1993;Greenfield et al, 2002;Grenier et al, 2002;Howard et al, 2005;Howe and Simenstad, 2011;Kleckner et al, 2010; Newsome et al, 2009Newsome et al, , 2012Rast, 1989;Sarakinos et al, 2002;Sydeman et al, 1997). Given large inputs of fertilizer and sewage into modern waterways, and extreme changes to the local ecology, especially the effects of invasive species, it is difficult to estimate how applicable modern data are to reconstructing ancient foodwebs in Central California (Wankel et al, 2006).…”

Carbon and nitrogen stable isotope ratios of macroinvertebrates in the littoral zone of Lake Biwa as indicators of anthropogenic activities in the watershed

“…All food source samples were treated with 0.1 N HCl to remove inorganic carbon and then dried at 60°C for more than 24 h. The foot muscle of snails and the adductor muscle of bivalves were resected and dried at 60°C for more than 24 h. Howard et al (2005) showed that the d 15 N value of mussels increased by approximately 2& with increasing age. In order to examine the relationship between body size and isotope signatures, we compared the dry weight of soft tissues and isotope signatures of macroinvertebrates for sampling sites at which more than three individuals were collected.…”