Grantee Research Project Results

Potential Shifts in Trophic Structure and Detrital Subsidies Within Intertidal Habitats Colonized by the Invasive Cordgrass, Spartina anglica (Poaceae), in Puget Sound, WA

EPA 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: Packard, Benjamin H
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

Objective:

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.

Approach:

We examined estuarine trophic relationships by sampling the stable isotopic composition ( delta ¹³C, d¹⁵N, and delta ³⁴S) of phytoplankton, zooplankton, benthic invertebrates, macroalgae, and vascular plants. Initial data using delta 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 ( delta ¹³C – 16 ‰) that is relatively similar to S. anglica ( delta ¹³C – 13 ‰). In bivariate isotopic scatterplots with delta 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 ( delta ¹³C – 21; delta ¹⁵N 9-10 ‰) that are different from those of Spartina ( delta ¹³C – 13 ‰, delta ¹⁵N ‰). Isotopic signatures of Macoma nasuta and Mytilus for delta ¹⁵N more closely resemble published values for phytoplankton (ca. delta ¹³C – 21; delta 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.

Supplemental Keywords:

fellowship, trophic, detrial subsidies, estuaries, Spartina anglica, cordgrass, invasive, interactions.

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.