PARENT SESSION
Poster Session 20: Invasive Species
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Ecosystem engineering by the invasive Spartina hybrid: impacts of above- and below-ground structure on benthic invertebrate communities.

Sorte, Cascade^{*,1, 2}, Grosholz, Edwin², Blake, Rachael², Christiansen, Nicole², Love, Christal², Mahl, Ursula², ¹ Bodega Marine Laboratory, Bodega Bay, CA² University of California-Davis, Davis, CA

ABSTRACT- Plants can variably affect the abundance and diversity of species in estuarine and marine systems by influencing temperature, light and flow environments. As the invasive hybrid Spartina (S. alterniflora x S. foliosa) continues to expand its range in San Francisco Bay (Calif., USA), there is a critical need to understand how Spartina influences the abundance and diversity of resident benthic communities. We designed a field experiment to examine Spartina's impacts by separately considering the effects of its aboveground (AG) and belowground (BG) structure. At a field site in Elsie Roemer Bird Sanctuary (Alameda, Calif.), we established 8 blocks of four habitat types or treatments. Uninvaded "Mudflat" and "Spartina" meadow contained neither or both AG and BG structure, respectively. AG structure was continually removed in the "Clipped" treatment, and a "Dowel" treatment consisted of wooden dowels embedded slightly in the mud to simulate AG, but no BG, structure. Treatments were established in July 2003, and samples of benthic infauna were collected in October 2003 and March 2004. For both sampling dates, both infauna richness and abundance were higher in the Dowel than the Mudflat plots and in the Spartina than the Clipped plots. These results matched those for epibenthic invertebrates, which were more abundant in Dowel vs. Mud and in Spartina vs. Clipped. There was no effect of treatment on Shannon-Wiener diversity on the October sampling date, but in March, infauna diversity was highest in the Dowel treatment. We suggest that, based on our temperature data, one of the primary effects of Spartina's AG structure is the buffering of heat stress. BG structure may exert its negative impact by reducing available habitat. Finally, an additional effect of the AG structure may be the selective facilitation of other introduced species.

Key words: Spartina, invertebrates, San Francisco Bay, salt marsh