PARENT SESSION
Oral Session #23: Aquatic Ecology: Salt marshes, estuaries, ephemeral wetlands.
Presiding: D. Childers
Monday, August 5. 1:00 PM to 3:45 PM. Palo Verde Room, Radisson.
Growth of invasive Spartina anglica seedlings in North Puget Sound, WA: Influence of intertidal position and native species interactions.
HELLQUIST, C. ERIC*,1, BLACK, R. ALAN1, 1 Washington State University, Pullman, WA
ABSTRACT- Over 40 years, Spartina anglica has become a dominant species of low intertidal zones associated with mudflat and adjoining salt marsh communities in northern Puget Sound, WA. A field experiment was established at three sites (Alice Bay, Maylor Marsh, and Swinomish Lagoon) to examine the growth of transplanted S. anglica seedlings in response to intertidal position and interactions with native species. In each intertidal zone, seedlings were planted within subplots where native plant species were intact (competition present) and where native plant species were removed (no competition). Spartina anglica seedlings had the highest growth rates in low and middle intertidal zones. Seedlings in low intertidal zones showed pronounced increases of tiller number, plant height, and leaf number (2-4x greater, ca. 2x greater, 8-10x greater). Reduced competition also favored S. anglica growth. Tiller number was markedly higher without competition compared to plots with competition (44 and 13 tillers respectively). However, in response to canopy cover, S. anglica mean height was greater with competition (275 mm vs. 166 mm). Conversely, high seedling mortality and reduced tiller and leaf production characterized high intertidal zones. High mortality (50% and 28% at two sites) in upper intertidal zones may result from desiccation stress and herbivory. Spartina anglica apparently is a less efficient competitor among native plants across intertidal zones. However, open substrates in low intertidal zones allow S. anglica to grow from isolated seedlings into multiple-tillered individuals during a single growing season.
KEY WORDS: Spartina anglica, invasive species, competition, estuaries