Research

My research program broadly addresses ecology, conservation and restoration of marine and estuarine systems. My work addresses questions at the intersection of community and ecosystem ecology that specifically include the impacts of human activities. The approaches I take reflect my training as a marine community ecologist, and ultimately I am interested in what determines the abundance and diversity of species in coastal systems. I am particularly interested in how human impacts have shaped community and ecosystem processes and how we can ensure the future health of coastal ecosystems through enlightened management based on good science.

Current work includes the following areas:

(1) Salt Marsh Restoration following Eradication of an Ecosystem Engineer
(2) Climate Change and Biological Invasions
(3) Restoration of Native Olympia Oysters Under Climate Change
(4) Human Enterprise and Vectors of Marine Invasions






Salt Marsh Restoration following Eradication of an Ecosystem Engineer

Much of my recent work over the last several years has involved measuring the community and ecosystem impacts of the invasive salt marsh cordgrass Spartina on a broad range of organisms from primary producers to shorebirds. This has been a collaborative project funded by the National Science Foundation (CNH Coupled Natural and Human Systems). Our previously funded project, a collaboration with Scripps Institution of Oceanography and SFEI focused on the impacts of invasive Spartinarange of community and ecosystem processes, particularly those involving benthic invertebrate communities and the sediment environment. Our results have shown that Spartina is truly an ecosystem engineer and that the structure of the plant itself changes the physical and chemical environment in ways that strongly influence benthic communities. Spartina attenuates light transmission to the substrate, reduces photosynthesis of benthic microalgae, and reduces water flow which results in decreased recruitment and growth of benthic suspension feeders. The plant structure also increases sedimentation rates and accumulation of detritus, which together with increased below ground plant biomass influence sediment chemistry and metabolism. The increased below ground biomass of Spartina also directly reduces benthic abundance and diversity. These physical and chemical changes result in dramatic shifts in benthic communities from larger surface-feeding taxa to subsurface detritivores, which are smaller and less available to higher trophic level consumers such as crabs, fish and birds. Understanding this balance of these effects will us develop a more general understanding of the impacts of introduced plants in coastal systems and will also help guide ongoing and future programs aimed at their eradication.

Our currently funded project through the NSF CNH Program focuses on the recovery and restoration of the salt marsh ecosystem following eradication of invasive hybrid Spartina. This work is a collaborative project with other UC Davis faculty including both scientists (Alan Hastings) and social scientists (Jim Sanchirico, Mark Lubell) to understand where, when and why this system may recover to its prior state. Following eradication of the invasive Spartina the system may recover either a marine mudflat or a habitat vegetated with native plants depending on tidal elevation. We are using a variety of experimental approaches involving habitat manipulations to accelerate or retard recovery, isotopic tracer studies to follow changes in food webs, long-term field surveys conducted both before and after eradication, and active restoration of native vegetation, in partnership with the SF Invasive Spartina Project to quantitatively assess the restoration process under a variety of conditions. With the social science collaborators, we are developing a bioeconomic model of the tradeoffs among eradication and restoration programs under different scenarios of agency participation that attempts to balance the invasive species eradication with the recovery of endangered California Clapper Rails.

For more information about invasive Spartina, see the following websites:

NSF Coupled Natural and Human Systems Project

San Francisco Estuary Invasive Spartina Project

 

Climate Change and Biological Invasions

Increasingly, my research is addressing the interaction between climate change and biological invasions. As the result of participation in an NCEAS (National Center for Ecological Analysis and Synthesis) working group on climate change and invasive species, I have continued my collaborative work on synthetic analyses of climate change impacts on the invasion process that began with participation in an NCEAS working group on climate change and invasive species. One project included a comprehensive study of field and lab experiments that varied climate change variables and assessed the impacts simultaneously on native and non-native species. The results of this analyses demonstrated that in terrestrial systems, native and non-native species responded similarly to experimentally manipulated climate change variables. However, in aquatic systems (freshwater and marine), increased temperature and CO2 more strongly impacted native species relative to introduced species. Overall, we found that with respect to future climate change projections, aquatic systems may be particularly at risk from invasions. This may help managers determine which systems should be the priority for reducing stressors that can be managed in order to lessen risks due to changing climates. In a second project, we brought together the few dozen studies that have documented the effects of extreme climatic events on biological invasions. As trends in temperature, pH, sea level rise and other markers of change increase, so does the magnitude and frequency of extreme events. Most of the evidence suggests that these events selectively facilitate successful growth and spread of existing invaders. This work is significant in bringing attention to two key issues. The first is the focus on extreme climate events, which are likely to have the greatest influence on ecosystem function in the future. The second issue is the effects on these rare events on invasions, since most other studies to date have only addressed the effects of mean values of climate variables on invader success. we developed a set of analytical tools for distributional and demographic data from invasive species to assess invasion potential at different invasion stages. We used data from three case studies (a vine, a marine mussel and a freshwater crayfish) using current and projected climatic conditions to generate three examples of this integrated assessment approach. Our results show that the particular climatic variables can have contrasting effects or operate at different intensities across habitat types that can be invasion stage specific. We found that projected climate trends may increase the likelihood of invasion in some habitats and decrease it in others. This approach is likely to provide information that can inform management decisions and help to optimize invasion phase-specific management efforts for a wide range of invasions.

NCEAS Working Group on Climate Change and Species Invasions



Restoration of Native Olympia Oysters Under Climate Change

An important focus of my work involves the ecology and potential for restoration of native Olympia oysters (Ostrea lurida) in western estuaries. Estuaries in California have been heavily impacted by human activities which have resulted in substantial loss of habitat, invasion by non-native species, inputs of sediments and contaminants and other stressors that have resulted in substantial declines in ecosystem function. One important approach to restoring these functions is the restoration of native species. Historically, native oysters likely provided the same ecosystem services that have been documented for native oysters in the eastern U.S. including the provision of habitat for native invertebrates and fishes and improving local water quality. There is now substantial interest on the part of many local, state, and federal agencies and natural resource managers in improving the health of California estuaries by restoring native oyster populations.

My research program now addresses climate change in the context of both limiting populations of native Olympia oysters as well as efforts to restore their populations. With funding from the NOAA/NERR Science Collaborative, and in collaboration with partners from San Francisco Bay NERR (Matt Ferner), Elkhorn Slough NERR (Kerstin Wasson) and UCD/SERC (Chela Zabin), we are investigating the effects of climate change variables on the future of restoration of this important foundation and fishery species in San Francisco Bay and Elkhorn Slough, CA. We are explicitly testing the influence of multiple climate change variables including sea surface and air temperatures, dissolved oxygen (hypoxia), and salinity on native Olympia oysters in both the lab and field settings. We have conducted lab experiments examining the influence of temperature, dissolved oxygen and salinity extremes on native oysters. We have also quantified these variables and others in field plots at multiple sites in SF Bay and Elkhorn Slough. The project will also develop a targeted set of decision tools for user groups involved with oyster restoration using substantial input from these groups in tool development. This work breaks new ground by examining multiple climate change variables by parameterizing experimental levels, durations and delays between stressors based on actual time series experienced in the field.

An additional focus of my work also involves large scale restoration projects involving simultaneous restoration of native oyster and eelgrass habitat. This project is funded by the California Coastal Conservancy and involves partnerships with San Francisco State University (Kathy Boyer), UCD/SERC (Chela Zabin), USGS (Susan de la Cruz), PWA (Jeremy Long), Environcorp (Bud Abbott), and CA Coastal Conservancy (Marilyn Latta). We are conducting restoration in plots distributed across several acres at two sites in SF Bay, an East Bay site at Eden Landing and a Marin County site on TNC lands. At these sites, both eelgrass and native Olympia oyster restoration is the goal using a variety of experimental recruitment substrata to encourage native oyster recruitment and experimental plantings of eelgrass to enhance growth of eelgrass beds. These are conducted explicitly to test methods for effectiveness and to understand the potential impacts and synergies of restoring these two habitats concurrently. An additional goal is to also understand the potential for the oyster recruitment structures to reduce wave energy and protect shorelines from erosion.

National Estuarine Research Reserve System (NERRS) Science Collaborative Project

San Francisco Bay Living Shorelines Project

Human Enterprise and Vectors of Marine Invasions

Part of understanding the invasion process and managing its impacts is identifying the mechanisms by which invasive species become introduced. With collaborators from UCD and Bodega Marine Laboratory (Susan Williams, Chela Zabin) and the Smithsonian Environrmental Research Center (Greg Ruiz), we received funding from the California Ocean Science Trust to examine the importance of aquaculture and the ornamental aquarium trade as vectors for introduced species into California. This project builds on and extends existing data bases documenting the identity of species and the most likely vector for introduction into California for several hundred species of fishes, invertebrates and seaweeds. Despite access to this data base, the current lack of knowledge prohibited our ability to quantify the relative importance of these vectors or even to rank most of them with any certainty. We were unable to reasonably quantify the flux of introduced species for several of these vectors. We were able to conclude that aquaculture is now a trivial vector for new invasions relative to its past importance. Also, we found that hull fouling is likely a more important vector than ballast water and was associated with the greatest number of invasions into California. These results are contained in two new reports and a synthesis publication. The results of this work will be immediately useful for CA resource managers concerned with reducing future invasions in CA.

Reports to the California Ocean Science Trust

Synthesis Paper



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