UC San Diego

Invasive species damage invaded ecosystems, displacing native species and decreasing biodiversity. In this study we focus on a specific invader, Argentine Ant (Linepithema humile), in the salt marshes of San Diego County. Argentine ants are a widespread and ecologically disruptive invader. Although ants are known to forage in intertidal environments, impacts caused by introduced ants in intertidal habitats are undescribed with no published information about ant foraging in Pacific coastal marshes. To learn more about the ecological effects of Argentine ant foraging in salt marshes we conducted an activity survey using baits to measure recruitment in marsh and adjacent upland habitat. Second, we conducted a lab experiment to test how saline conditions affect colony growth. Last, we used stable isotope analysis to determine the extent to which the Argentine ant assimilates resources from intertidal environments by comparing this invader with a native ant (Dorymyrmex insanus) and fiddler crabs (Uca sp.). Our lab experiment showed that there is no significant effect of salinity on ant colony growth. Our activity surveys revealed that the Argentine ant occurs commonly in intertidal marsh habitat with activity levels not different from those observed in adjacent upland habitat. Stable isotope analyses showed that the Argentine ant had a significantly higher δ15N value and a significantly lower δ13C compared to D. insanus. This study is the first known to measure Argentine ant foraging behavior in salt marshes in San Diego. Our results indicate that Argentine ants readily invade salt marshes in a similar manner as terrestrial habitats.