Heidi Weiskel

Ph.D. student (entered 2003)

Research interests: biological invasions, disturbance, estuaries, community ecology

Project: Understanding the impacts of nutrient pollution on species interactions and biological invasions in marine habitats.



Postdoc (starting Spring 2011)


I am finishing my dissertation and will be starting a postdoctoral position with Dr. James Byers at the University of Georgia in March 2011. I will be working on a large NSF-funded biogeographic study on oyster ecosystem function and predation along the southeastern coast of the United States. Eventually I plan to incorporate our work in this temperate estuarine system into tropical habitats in Panama and Cuba, as I am interested in understanding how allocthonous resources affect community dynamics along latitudinal gradients and across tidal gradients.



Dissertation: Nutrient loading and consumer invasion dynamics in temperate estuaries


Nutrients and invasion dynamics at higher trophic levels

My research focuses on the role of resources and their impacts on species interactions and community dynamics in marine systems. For my dissertation research I was particularly interested in the effects of nutrient loading as an abiotic disturbance on native and invasive gastropod species in San Francisco Bay. My work focused on how nutrients affect primary producers, which in turn affect consumers in estuarine communities. What effects do increased nutrients have on marine species? Do nutrients affect invasive species differently than native species? Can nutrient loading shift the competitive balance in favor of marine invasive species, thereby potentially accelerating the invasion of future as well as current introductions? Are there generalities across taxa? Trophic levels? Are there thresholds within these marine systems, whereby nutrients shift from being a critical resource to a pollutant? Are upward, resource-driven cascades as important as the top-down effects of predation?


Our current understanding of the relationship between nutrients and invasive species is largely based on responses measured in terrestrial primary producers. Studies of terrestrial plants have shown that invasive species capable of fixing nitrogen or partitioning nutrient resources can edge out their competitors (Ehrenfeld 2003, Fargione et al. 2003, Levine et al. 2003). In these systems, therefore, increased nutrients facilitate the spread of plant invasions. However, these same relationships remain relatively unexamined in marine systems and for higher trophic levels.


I tested the resource advantage explanation for invasion success in this new context by examining the disturbance caused by high nutrient influx into the nearshore benthic environment in San Francisco Bay. My hypothesis was that the added nutrients would shift the microalgal community from diatoms to cyanobacteria, which in turn would favor the invasive snail over the native one, because the invader has a broader diet niche and could better tolerate the switch. I worked with the Atlantic mud snail Ilyanassa obsoleta—introduced to the west coast in the early 1900s—and the sympatric native mud snail Cerithidea californica. Using a factorial design with nutrients and species combinations in the field and HPLC and stable isotope techniques in the lab, I tested how competitive interactions, growth rates and sediment characteristics are altered by nutrient additions, via changes to the microphytobenthic community. I also ran a behavioral experiment to assess whether the snails preferred certain microalgal communities (diatoms v. cyanobacteria), and whether preferences were influenced by either nutrients or species identity.


New invasions

In 2005 we found the first reported population of the Japanese mud snail Batillaria attramentaria in San Francisco Bay. Then, in the spring of 2007, we found another population in Bodega Harbor. We have been characterizing the growth and spread of these populations in both locations and comparing them to the established population in nearby Tomales Bay. The new invasion also provides an opportunity to study the habitat impacts of these new invasions. And some members of our research team have even worked on assessing the efficacy of several eradication methods.


Nutrient loading and invasive species are unlikely to disappear as threats to estuarine systems but a greater understanding of their interactions and effects on native species—as well as their demographic characteristics as founder populations—can facilitate better protection for native species and the habitats on which they depend. As human development pressure mounts along the coasts, studies that connect pollution and ecosystem health are increasingly important, as are broader studies that deepen our understanding of the relationships between resources and species interactions. I look forward to continuing these research ideas at UGA in 2011.



Cerithidea californica and Ilyanassa obsoleta in nutrient loading trials in San Francisco Bay.


Batillaria attramentaria new population discoveries in San Francisco Bay and Bodega Harbor.


My graduate school research has been supported by the National Science Foundation (NSF) BioInvasions Integrative Graduate Education and Research Traineeship (IGERT) at UC Davis, the San Francisco Bay National Estuarine Research Reserve (SFB NERR) Graduate Research Fellowship, an Environmental Protection Agency-Science to Achieve Results (EPA-STAR) Fellowship, and a Science Fellowship through the California-Federal Bay-Delta (now Delta Science) program.

CV in pdf format
Keywords: marine invasions, nutrient loading, native-invasive competitive interactions, disturbance ecology, resource ecology, primary production, estuarine dynamics, eutrophication, founder populations, Ilyanassa obsoleta, Cerithidea californica, Batillaria attramentaria

Grosholz Lab Ted Grosholz Research Cooperative Extension Grad Students Postdocs Lab Staff Lab Alumni Links and Resources Site Map