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Potential Shifts in Trophic Structure and Detrital Subsidies Within Intertidal Habitats Colonized by the Invasive Cordgrass, Spartina anglica (Poaceae), in Puget Sound, WAEPA Grant Number: U916168
Title: Potential Shifts in Trophic Structure and Detrital Subsidies Within Intertidal Habitats Colonized by the Invasive Cordgrass, Spartina anglica (Poaceae), in Puget Sound, WA
Investigators: Hellquist, Carl E.
Institution: Washington State University
EPA Project Officer: Graham, Karen
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $98,710
RFA: STAR Graduate Fellowships (2003) Recipients Lists
Research Category: Academic Fellowships , Biology/Life Sciences , Fellowship - Biological Sciences
The objective of this research project is to examine trophic relationships following colonization of a nonnative species. Spartina anglica is an invasive estuarine cordgrass that has colonized approximately 400 ha of intertidal habitats in north Puget Sound, WA. This invasion has resulted in the extensive colonization of some mudflats while other similar mudflats may have little or no Spartina present.
We examined estuarine trophic relationships by sampling the stable isotopic composition (13C, d15N, and 34S) of phytoplankton, zooplankton, benthic invertebrates, macroalgae, and vascular plants. Initial data using 15N and d13C indicate that invertebrate isotopic ratios vary between sites and species. Macoma balthica (Bivalvia) collected within roots of S. anglica has a C signature (13C – 16 ‰) that is relatively similar to S. anglica (13C – 13 ‰). In bivariate isotopic scatterplots with 15N, Macoma balthica is placed closer to Spartina than it is to other bivalves. This placement may indicate the use of some Spartina-derived carbon. However, Macoma nasuta (Bivalvia) and Mytilus edulis (Bivalvia) collected among Spartina have coinciding isotopic signatures (13C – 21; 15N 9-10 ‰) that are different from those of Spartina (13C – 13 ‰, 15N ‰). Isotopic signatures of Macoma nasuta and Mytilus for 15N more closely resemble published values for phytoplankton (ca. 13C – 21; 15N 9-10 ‰). These data suggest that despite living among the roots of small Spartina clones (Macoma nasuta) or living attached to the base of Spartina stems (Mytilus), these bivalves are not using Spartina productivity for nutrition.