Multiple stressors have mixed effects in an experimental Spartina alterniflora - herbivore system

Rachael E. Blake, Jill A. Olin


     This will say something brilliant about this experiment. 


          Multiple-stressors are threatening coastal ecosystems around the globe, yet their simultaneous impacts remain difficult to test and predict because stressors can interact to produce ecologically surprising effects (Paine 1998).  These potential interactions between stressors present some of the biggest uncertainties in understanding and predicting ecological change in coastal systems (Piggott 2015).     
          Define "stressor" as a biotic or abiotic factor that causes a species or population to vary significantly more than usual.    

Expected effects of stressors from ecological theory and previous work. 
        Expected synergisms; double negative impacts greater than additive.
        Stressor interactions are frequently assumed to be synergistic (Whitehead paper), especially between anthropogenic stressors, and sometimes even between biotic and anthropogenic stressors (Sih paper 2004).  However, this cannot be assumed to always be the case, and thus we need to test the effects of stressors simultaneously. 

Saltmarshes are important in general. 
        Habitat for juveniles, carbon storage, coastal protection
In Louisiana they are particularly important for species habitat and for coastal protection. 
Yet saltmarshes are vulnerable.  Plants can be impacted by biological factors such as herbivory. 
          Cite the Silliman work and work on the Prokelisia. 
But more acute threats in Louisiana are anthropogenic and include oil spills.  
            Exposure of marshes to background and previous spills. 
            The Deepwater Horizon oil spill, which released 200 million gallons of crude oil into the Gulf of Mexico, gave us the opportunity to study the acute impacts of oil in these important ecosystems (Crone 2010).  In the efforts to clean up the spilled oil and prevent it from washing on shore, 1.84 million gallons of chemical dispersant were also released into the environment (Drilling 2010).  While the majority of the spill and cleanup activities occurred offshore, the unprecedented amount of oil spilled and dispersant used in the cleanup led us to hypothesize that this spill event might have unpredictable impacts in saltmarsh ecosystems. 

           We took an experimental mesocosm approach to test simultaneous multiple-stressor effects, both biological (herbivory) and chemcial (oil and dispersant), on the key saltmarsh foundation species, Spartina alterniflora.  Our fully factorial experiment used insect and snail herbivores as well as oil and dispersant as stressors, and measured responses in both the plants and herbivores.  We analyzed the resulting data for direct and indirect interactions to comprehensively examine all potential pathways of impact.  Our overarching goal was to determine the nature of interactions between biological and chemical stressors in model saltmarsh systems.