Some of the most striking examples of community change appear to be driven by changes in the abundance of particular species with cascading effects on other members of an ecosystem. Seabirds exert substantial effects through predation and by modifying abiotic factors, thereby determining species richness of assemblages in both marine and terrestrial habitats. In New England, gulls have increased dramatically since the early 1900s, and are likely transforming coastal terrestrial and intertidal communities through their activities. However, their impacts are virtually unknown. The goal of this research is to understand the mechanisms by which nesting gulls impact plant (terrestrial herbaceous and intertidal algae) assemblages. Gulls may have top-down effects on algal diversity in the intertidal through predation on secondary consumers (crabs) that forage on algal grazers (littorines). Birds transfer marine-derived nutrients and energy from intertidal to terrestrial habitats via guano, and as a consequence they may impact terrestrial plant diversity from the bottom-up. I propose a combination of experimental manipulations and comparative sampling methods to investigate these effects. Policies in aquatic ecosystems (e.g. seabird restoration) can affect both aquatic and terrestrial systems. Understanding gull impacts in marine and terrestrial habitats will contribute to informed management practices.
