Community and trophic consequences of the introduction of Spartina anglica C. E. Hubb. (Poaceae; English cordgrass) in estuaries of Puget Sound, Washington, United States of America

Spartina anglica C. E. Hubb. (Poaceae) is an invasive cordgrass in estuaries of the northeastern Pacific Ocean. The growth of Spartina seedlings in the presence or absence of native vegetation was measured across the intertidal gradient at two sites. Spartina seedling survival and growth parameters were greatest in low intertidal zones. Unmanipulated seedlings growing in open mudflat where neighboring vegetation was absent had the greatest biomass production (mean 433 g individual -1). Low intertidal zones characterized by Salicornia also were conducive to Spartina growth (mean 81 and 174 g individual-1 with and without neighbors, respectively). At the second site, Spartina growth was greatest in the absence of native neighbors in all zones. Spartina growth in the Distichlis zone without neighbors was 1.6 fold greater than the Salicornia zone at the second site. Biotic resistance along gradients of interacting physical conditions can impede the establishment and slow the vegetative expansion of Spartina.; Multiple stable isotopes (delta13C, delta15 N, and delta34S) and IsoSource stable isotope mixing models were used to determine whether three bivalve species consumed Spartina biomass at two sites. The clams Macoma balthica (34-64%) and Mya arenaria (20-62%), had the greatest Spartina dietary contributions while the mussel Mytilus trossulus had Spartina dietary contributions of 10-48% at the high Spartina canopy cover site in March. During July, the diet of Macoma consisted of 42-66% Spartina while the importance of Spartina was greatly reduced for Mya and Mytilus. Spartina biomass was a food source Mytilus. Spartina biomass was a food source for bivalves during winter, but its dietary importance was less during the growing season and at the low Spartina canopy cover site.; Mudflats with intact or managed Spartina populations have lower oxidation-reduction potentials (ca. -300 mV) than uninvaded mudflats (ca. -50 mV), high concentrations of Spartina organic matter in sediments (ca. 700-900 g m-2), and different associations of macroalgae and vascular plants. The sand clam (Macoma balthica ) showed a decline in abundance associated with sediments colonized by Spartina (r2 = 0.57 to 0.79; P < 0.001). Once meadows of Spartina coalesce on littoral mudflats, Spartina modifies chemical and physical conditions that influence the succession of macroalgae, vascular plants, and bivalves.