PARENT SESSION
Oral Session #70: Invasive Species: Aquatic.
Presiding: S. Juliano
Wednesday, August 7. 1:00 PM to 4:45 PM. Grand Ballroom East, Radisson.
Distribution of exotic cordgrasses (Spartina sp.) in the tidal marshes of San Francisco Bay.
AYRES, DEBRA*,1, SMITH, DEBRA2, ZAREMBA, KATHERINE2, KLOHR, SHANNON2, STRONG, DONALD1, 1 UNIVERSITY OF CALIFORNIA, DAVIS, drayres@ucdavis.edu2 CALIFORNIA COASTAL CONSERVANCY, OAKLAND
ABSTRACT- Four species of exotic cordgrass, Spartina densiflora, S. patens, S. anglica, and S. alterniflora occur in the San Francisco estuary in addition to the California native S. foliosa. Spartina alterniflora has hybridized with the native species, producing large numbers of highly fit hybrids. Our goals were to characterize the appearance of S. foliosa, S. alterniflora and hybrid plants, genetically evaluated by RAPDs, to enable visual identification of these entities in the field, and to map the location and extent of all non-native Spartina in the estuary. We found that greater height, biomass, culm width and intensity of red culm color were indicators of S. alterniflora and hybrid genotypes. We found populations of one or more species in each subregion of the Bay with a net cover of 195 ha - less than 1% of the Bay's mudflats and marshes. Spartina alterniflora and hybrids covered almost 190 ha, mainly in the South and Central Bay, radiating from deliberate introduction sites. Spartina anglica has not spread beyond it's original 1970's introduction site; S. densiflora is actively spreading, covering over 5 ha at 3 sites in the Central Bay; S. patens has expanded from 1 to 42 plants at a single site in Suisun Bay. We found isolated plants of S. alterniflora and S. densiflora in outer coast estuaries north of the Bay highlighting the need to survey Pacific estuaries for invasive exotic cordgrasses.
KEY WORDS: Spartina alterniflora, Invasive species