MS Thesis Defense - Natasha Breaux

SUBJECT: Ecosystem Resilience Following Salinity Disturbance in a Hypersaline Estuary

COMMITTEE CHAIR: Dr. Jennifer Pollack

COMMITTEE: Dr. Paul Montagna, Dr. Greg Stunz, Dr. Benoit Lebreton (University of La Rochelle)

Salinity variability can act as a disturbance to benthic macrofauna communities in estuarine systems, which has indirect effects on higher trophic levels. Climate models predict changes in precipitation patterns will increase future hydrological variability, particularly in the southwestern United States where precipitation events will become less frequent but more intense. The Baffin Bay Complex (BBC) is a predominantly hypersaline estuary adjacent to the more hydrologically stable Laguna Madre in the semi-arid region of South Texas, USA. The Baffin Bay-Laguna Madre system supports large populations of Pogonias cromis, a commercially important benthic predator. In 2012, P. cromis in the BBC experienced a widespread emaciation event, but a lack of hydrological and benthic community data preceding this event made determination of potential causes difficult. This study utilized infaunal community characterization, stomach content and stable isotope analyses to evaluate the functioning of the BBC food web over a range of hydrological conditions. Salinity was found to be the best predictor of macrofauna changes in the BBC, with community metrics primarily driven by the opportunistic bivalve species, Mulinia lateralis. The difference in primary producers in the phytoplankton-dominant BBC and seagrass-dominated Laguna Madre causes isotopically distinct organic matter and benthic food resources. Isotopic analyses of muscle tissues suggest that P. cromis utilize resources from both the BBC and Laguna Madre under normal estuarine salinity conditions, but are restricted to the BBC under hypersaline conditions. This spatial restriction is possibly due to the energetic cost of osmotic regulation in hypersaline conditions, which in turn inhibits locomotion out of the BBC. Understanding the impacts of salinity variability on benthic prey availability and trophic interaction dynamics is critical to determining the ecosystem-scale effects of salinity disturbance.