PARENT SESSION
Symposium 6: Anthropogenic Modification of North American Salt Marshes: Causes, Consequences and Recommendations
Organized by: B Silliman
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Chatham Ballroom C.
Ecological and Evolutionary Misadventures of Alien Spartina alterniflora in the Pacific.
Strong, Donald*,1, Davis, Heather2, Ayres, Debra1, Taylor, Caz3, Civille, Janie3, Lambrinos, John4, 1 Section of Ecology and Evolution, Davis, CA, 956162 Population Biology Graduate Group, 95616, CA3 Ecology Graduate Group, Davis, CA, 956164 Dept. of Environmental Science and Policy, Davis, CA, 95616
ABSTRACT- This is a tale of two estuaries being invaded by smooth cordgrass, Spartina alterniflora, a native of Atlantic saltmarshes that substantially affects organisms, hydrology, and the commercial uses of Pacific estuaries where it invades. With no seedbank, it disperses almost exclusively by seed-of-the-year that floats on the tide. In Willapa Bay, WA, far north of native cordgrass, S. alterniflora colonizes mudflats that previously had no emergent vegetation, converting them to cordgrass meadow and resulting in the loss of habitat for native species, fishing, and mariculture. Spread of this invasive has been roughly exponential since its introduction 100 years ago, and it is now present throughout the 43 km long Bay. The spread has been attenuated by an Allee effect in which colonies at the leading edges of the invasion set little viable seed, probably for want of outcross pollen from too-distant neighbors. Recruitment in some years is low. In San Francisco Bay, S. alterniflora has hybridized in the last 25 years since its introduction with the native California cordgrass, S. foliosa. Extensive hybrid swarms are sweeping parts of the Bay, and both the native and alien parents have virtually disappeared from these areas. Hybridization is reciprocal, and both parental species have been seed parents to hybrids. Pollen swamping of natives by hybrids probably drives spread of the hybrid swarm. Hybrids have higher fitness than either parent, and accelerating hybridization threatens the very existence of California cordgrass.
Key words: invasive, Allee effect, Spartina, salt marsh