Jennifer E. Smith's Research

Overview


My research focuses on understanding the factors (natural, anthropogenic, physical & biological) that influence community structure in benthic marine ecosystems. While I conduct research in a number of different systems, both pristine and degraded, my primary interests lie in determining how different anthropogenic impacts affect coral reef community structure. When coral reefs undergo degradation, a "phase-shift" usually occurs where reef-building corals are replaced by fleshy macroalgae. Phase-shifts are often considered to be irreversible and the end result is a macroalgal dominated community that lacks the diversity, complexity and structure necessary to support a typical reef assemblage. I have and continue to study various anthropogenic factors that cause phase shifts from coral to algal dominance. Specifically my research focuses on the importance of herbivory (or overfishing) and increased nutrient concentrations (in association with pollution from land) in maintaining the competitive balance between algae and coral. Further I study the dynamics of introduced and innvasive marine species, specifically seaweeds. With this work I have taken a holistic approach by trying to understand a) why these invaders are so successful in their invaded environments, b) what impacts they have on native communities and c) what management options will be useful in controlling their abundance in the invaded habiatas. I have a long-term interest in seaweed invasions especially as related to intentional introductions for the aquaculture industry. My research often goes beyond basic ecology by integrating conservation, restoration, management and sustainability. More recently I have been investigating the interactions of microbes and macrobes on coral reefs and have shown that these indirect interactions may be highly important to overall community structure and function. In the future I plan to begin investigating the potential for reef restoration in an effort to understand if phase-shift reversal is possible. 


 

Current Research Interests

 

(1) The Effects of Top-Down (Grazing) and Bottom-Up (Nutrient Input) Factors on Coral Reef Benthic Communities

 

How does overfishing & nutrient pollution alter competitive dynamics and species assemblages on coral reefs? 

 

How do shifts from coral to algal dominance occur? What are the ecosystem consequences of these alternate stable states?

My doctoral research addressed a long-standing debate in the coral reef ecology as to whether nutrient enrichment or reduced herbivory was more important in causing large-scale phase-shifts from coral to algal dominance on coral reefs. Through field experimentation I have shown that both factors can independently and synergistically change species assemblages and community structure (Smith et al. 2001). I found that herbivores are highly important in controlling fleshy algal biomass while nutrients increased the abundance of calcifying coralline algae; however, the combination of reduced herbivory and increased nutrients led to communities that were dominated by fast growing macro algae. The re-introduction of herbivores at the end of the experiment led to a complete reversal in successional trajectories, shifting communities back to a state similar to controls (Smith in prep). These results suggest that on degraded reefs, recovery of herbivore populations may promote a phase-shift reversal by reducing the abundance of fleshy algae and opening space for reestablishment of reef building organisms.

As a postdoctoral fellow at the National Center for Ecological Analysis and Synthesis, I have increased the spatial and temporal scope of analyses on the importance of top-down and bottom-up control on coral reefs. Similar to the results of my experimental work, I have shown using a large-scale meta-analysis of data from across the globe that both nutrient enrichment and herbivore abundance regulate benthic reef communities. Most importantly high levels of herbivory tends enhance the abundance of crustose coralline algae, an important settlement surface for coral larvae while nutrient enrichment increases algal growth rates but not necessarily abundance. Finally, the combined effects of herbivore removal and nutrient enrichment can result in communities dominated by weedy macroalgae suggesting that management efforts should focus on both overfishing and eutrophication (Smith in prep.). 

 

(2) Marine Invasive Species

 

What factors influence invasion success?

What are the impacts of invaders on community structure?

What kinds of conservation or management efforts can be used to reduce or minimize the impacts of invaders?

Are there trends in global seaweed invasions as related to taxonomy, morphology, biogeography, vector of introduction and impacts or resistance to native communities?

Despite the widespread introduction of exotic marine species around the globe, very little information is known about the biology or ecology of these invaders in their new environments. Using the Hawaiian Islands as a case study, I sought to characterize the extent of seaweed introductions with an effort to understand various components of the system that may facilitate invasion and to determine the influence of the invaders on community structure. After conducting a series of state-wide surveys I was able identify that several species had become ecological dominants and were forming blooms to varying degrees across the islands (Smith 2002). Detailed laboratory experiments were conducted to determine the response of these species to temperature, salinity, nutrient concentrations and herbivory and these results proved to be useful for predicting the distribution of each of these invaders around the state (Conklin and Smith in prep). More focused research has since been conducted on the ecology of individual species with the goal of identifying potential management solutions (Smith et al. 2004, Conklin and Smith 2005, Smith et al. 2005). 

Using classic ecological theory and a multidisciplinary approach, I sought to understand the ecology and develop management options for the red alga Eucheuma denticulatum, one of the most successful marine invaders in Hawai’i. This species is of particular importance because it has been introduced to more than 20 countries across the globe for commercial aquaculture with no regulatory oversight or risk assessment (Zemke-White and Smith 2006, Schaffelke, Smith and Hewitt 2006).  I have found that this species is able to invade diverse and structurally complex reefs and after invasion has occurred it can readily reduce species diversity, coral cover and habitat complexity thus altering the structure and function of the reef community (Smith et al. in prep, numerous academic awards have been received for this work, see C.V.). These results represent the first quantitative and experimental assessment of the impacts of an invader on a coral reef and highlight the need to study the invasion potential of aquaculture species across the globe.

Throughout my academic career I have worked closely with natural resource managers, conservation biologists and professionals in other disciplines including economists and sociologists to integrate my scientific findings into policy. Through a large collaboration I have helped to develop community based invasive algae removal programs in high profile areas such as Waikiki Beach, Hawai’i. This collaboration was recognized in 2003 with a multi-agency Coastal America Partnership award. Further, working in an area inundated with invasive algae on Maui I helped to inspire an economic valuation of the impacts of the seaweed invasion on tourism, property values and mitigation efforts. This valuation was then used to acquire more funding to understand the ecological impacts and invasion dynamics of this species (Smith in prep.). Lastly working with state, federal and nongovernmental agencies I have helped to draft the Hawai’i Marine Invasive Species Management Plan and have established invasive species removal programs using a combination of herbivore stock enhancement and manual removal to reduce the abundance and minimize the impacts of these species on Hawai’i’s reefs.   

As a postdoctoral fellow, I have continued my research on invasive species taking more of a global perspective. Through collaboration with colleagues in Australia we completed a review on the process of invasion from transport and dispersal to establishment and spread (Schaffelke, Smith and Hewitt 2006). More recently I have developed the only comprehensive database on global seaweed introductions with a focus on ecological impacts and risk assessments with Dr. Susan Williams at Bodega Marine Lab, UC Davis. We have just completed an invited review that will be published this year in Annual Reviews (Williams and Smith 2007). 

 

(3) Coral-Algal-Microbe Interactions

 

Are there microbially mediated  interactions between algae and corals that could help to explain phase-shifts on tropical reefs?

Recent research has shown that reef building corals are not affected directly by increased nutrients that are most often associated with eutrophication (nitrogen and phosphorus) but that dissolved organic carbon (DOC) will cause coral mortality as a result of increased microbial activity and subsequent smothering and hypoxia. Through a multidisciplinary collaboration we hypothesized that tropical algae may release DOC into the environment as excess photosynthate (most primary producers across the globe are known to exude DOC), and that this will enhance microbial activity and cause coral mortality. In a series of experiments we found evidence that this mechanism exists and that the effectiveness of algae and the susceptibility of coral varies among species. We believe that this mechanism may be incredibly important in helping to explain how phase-shifts from coral to algal dominance occur specifically by setting up a positive feedback loop whereby increases in algae (caused by overfishing, nutrient enrichment, bleaching, etc.) fuel microbial activity and cause local coral mortality; this opens up more space for algal colonization and thus more exudation and microbial activity and so on until a phase shift has occurred (Smith et al. 2006). These novel findings identify a level of complexity in reef health and restoration not previously realized on coral reefs. Current research on early life stages of corals has revealed similar conclusions, suggesting that this mechanism of coral-algal-microbial interactions to be fairly ubiquitous (Vermeij, Smith, et al. in prep.) and clearly worthy of more detailed investigation. 
 

 

Past Research Projects & Associated Web Pages

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