Ecosystem resilience following salinity change in a hypersaline estuary
Breaux, Natasha Johnson
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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. Baffin Bay is a predominantly hypersaline estuary adjacent to the more hydrologically stable Laguna Madre in the semi-arid region of South Texas, USA. Baffin Bay and the Laguna Madre collectively support large populations of Pogonias cromis, Black Drum, a commercially important benthic predator. In 2012, P. cromis in Baffin Bay 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 used infaunal community characterization, stomach content, and stable isotope analyses to evaluate the functioning of the Baffin Bay food web over a range of wet and dry conditions. Salinity was the best predictor of changes in macrofauna biomass, abundance, and diversity in Baffin Bay, with community biomass and diversity primarily driven by the opportunistic bivalve species, Mulinia lateralis. The difference in primary producers in the phytoplankton-dominant Baffin Bay and seagrass-dominated Laguna Madre causes isotopically distinct organic matter and benthic food resources. Isotopic analyses of muscle tissues indicate that P. cromis use resources from both Baffin Bay and the Laguna Madre under normal estuarine salinity (≤ 35) conditions, but are more constrained to Baffin Bay under hypersaline (> 35) conditions. This spatial restriction is possibly due to the energetic cost of osmotic regulation in hypersaline conditions, which may limit movement of euryhaline fish. Understanding the impacts of salinity change on benthic prey availability and trophic interaction dynamics is critical to determining the ecosystem-scale effects of salinity variability.
A thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in MARINE BIOLOGY from Texas A&M University-Corpus Christi in Corpus Christi, Texas.
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Breaux, Natasha Johnson