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Research
(i) Defining physical characteristics of nekton habitats in estuarine environments
Photos
A research focus relates to a central tenet of ecology that habitat complexity affects species abundance and richness. With this research, I seek to better identify nekton habitats by examining the role of habitat complexity (both temporal and spatial) in structuring nekton communities. This research seeks to elucidate complexity measures in the estuarine environment that can be used to understand nekton use of shallow-water habitats. It is only by accurately defining the habitat needs of an organism that we can better manage and restore critical habitat. Research projects in Louisiana estuaries conducted by graduate students and research associates since 2001 have begun to identify critical physical habitat metrics on nekton communities that may help better define nekton community. This projects range from work in submerged aquatic vegetation examining landscape characteristics and their links to nekton communities and nekton growth; to studies along marsh edges examining edge morphology and nekton use, and a study examining nekton use of flat oyster reefs in coastal Louisiana.
(ii) Effects of salinity variability on nekton and oyster-parasite dynamics
Temporal variation in key physicochemical conditions at a site is often listed as critical to an organism’s existence. Since 2001, I have been engaged in research that examines the effects of variability in salinity, versus mean salinity, on oyster condition and nekton communities and growth. With freshwater diversions, and pulsed diversions being one of the main restoration vehicles in coastal Louisiana, I have developed a program that uses these controlled freshwater events to better understand the effects of variability in salinity (and other affected factors such as temperature), on organisms. Initial results regarding the effects of salinity changes (i.e., freshets) on oyster-parasite dynamics indicate that rapid salinity changes may be more important in controlling the outcome of these dynamics than mean annual salinity. For nekton, it is not known how this impacts fisheries communities or marsh productivity; ecological theory suggests that freshwater pulses provide an energy subsidy downstream. Along with intense field investigations of nekton responses, we are evaluating fish growth to determine estuarine resident fishes role in the transfer of energy across the marsh.
(iii)Wetland restoration Photos
Recommendations on restoration techniques and restoration design in wetland and aquatic habitats have largely been hampered by a lack of standards for monitoring, and an almost complete lack of monitoring for nekton. To address this problem, I have been pursuing a line of research that involves the identification of quantifiable nekton habitat metrics for comparison and valuation of nekton habitat.
Specific projects are examining two popular restoration techniques: thin-layer sediment application and marsh terracing.
Thin-layer spray dredge is becoming the “new” approach to marsh restoration with recent EPA sponsored workshops to examine the feasibility of long-distance conveyance of sediment via pipelines for such purposes. Essentially, a layer of dredged sediment is sprayed or slurried over the marsh surface, at a thickness that adds much needed sediment, but does not negatively impact the marsh. It has been suggested that this sediment addition may add, along with much needed elevation, a nutrient pulse to degrading marshes that will boost plant production, and thus enhance organic matter production. Few data exist however regarding the long-term effects of spray dredging, and fewer still have collected pre and post restoration data. This project is measuring key plant and soil parameters at a 6 sites ranging in age from 0 to 7 years in coastal Louisiana.
Marsh terracing is a commonly used marsh restoration technique in coastal Louisiana. Over 400 km of terraces at an average estimated cost of $33/m have been created to date in Louisiana. Terraces are formed by piling up sediment in discontinuous levees in eroding open water ponds. Along with a co-PI (Dr. Andy Nyman, School of Renewable Natural Resources) who focused on vegetation impacts, I examined the functional equivalency of created marsh terrace edges with unmanaged marsh edges, in terms of provision of nekton habitat. An initial study which found that terraces did not in fact provide many of the hypothesized benefits to the system generated much interest, and led to a much larger study which allowed us to examine the development of multiple marsh terrace ponds, and their functional equivalency with unterraced ponds.
(iv)Ecology of oyster reefs in the Gulf of Mexico
In other parts of the nation, oyster reefs are highly valued for the habitat services (food and refuge) that they provide for nekton, and in shoreline protection, largely due to their 3 dimensional structure. In Louisiana, few remaining oyster “reefs” have a significant height component, as evidenced by the fact that the vast majority of oyster growing areas are cultched with oyster shell for harvest. This cultching does create oyster reefs, but they are maintained as a flat structure. I have been involved in studies examining the role of cultched reefs in supporting nekton, including investigating the diets of nekton found inhabiting the reefs as well as studies investigating the role of these reefs in reducing wave energies and hence, protecting shorelines. With new emphasis on shoreline protection in coastal Louisiana, we are currently looking at expanding this research to a larger scale study. This research has also led to an interesting collaboration with the Global Coral Reef Alliance (www.globalcoral.org), where we are investigating the use of the BiorockTM Reef in coastal Louisiana in terms of spat recruitment and oyster growth as a potential new tool for creating shoreline protection structures.