PARENT SESSION
Oral Session # 25: Invasive Species II: Aquatic Systems.
Presiding: G Rilov
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 205.
Multi-trophic level and ecosystem changes following the Spartina invasion of San Francisco Bay.
Grosholz, Edwin*,1, Levin, Lisa2, Neira, Carlos2, Tyler, A.1, 1 University of California, Davis, Davis, CA, USA2 University of California, San Diego, La Jolla, CA, USA
ABSTRACT- The 1975 introduction of Spartina alterniflora introduction into San Francisco Bay, CA (USA) and subsequent hybridization with the native S. foliosa produced a hybrid that has dramatically altered the historically unvegetated mudflats below the tidal distribution of native plants. The invasive hybrid reduces light (100X), reduces water flow (2X) and reduces variation in sediment accretion (2-5X). In areas colonized by Spartina, faunal densities have declined by >70%, diversity and richness are lower and species composition has shifted significantly. For selected taxa, experimentally determined recruitment and growth rates are lower in Spartina compared to unvegetated mudflat. However the abundances of several exotic molluscs are higher (2-10X) in the expanding margin of the hybrid indicating it is facilitating some introduced species. Experimental sediment transplants from mudflat into the hybrid and vegetation removal experiments provide support for the conclusion that the hybrid invasion is responsible for these changes. Changes in faunal abundances, increases in total organic matter, silt/clay fraction, soil temperature, sulfide, ammonium and chl a all occur rapidly post manipulation. At higher trophic levels, grazing Canada geese are being affected by declining distributions of native S. foliosa. Field data and exclosure experiments in the field show hybrid Canada geese graze heavily and selectively on native S. foliosa during winter nesting periods and ignore the hybrid Spartina. Feeding experiments with captive geese support these observations. These results suggest that hybrid Spartina is dramatically altering community structure, trophic transfer and ecosystem processes in this system.
Key words: Spartina, infauna, introduced species, Canada geese