Pollack, Jennifer BeseresBreaux, Natasha Johnson2017-11-012017-11-012017-08http://hdl.handle.net/1969.6/5622A 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.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.79 pages.en-USThis material is made available for use in research, teaching, and private study, pursuant to U.S. Copyright law. The user assumes full responsibility for any use of the materials, including but not limited to, infringement of copyright and publication rights of reproduced materials. Any materials used should be fully credited with its source. All rights are reserved and retained regardless of current or future development or laws that may apply to fair use standards. Permission for publication of this material, in part or in full, must be secured with the author and/or publisher.Baffin Baybenthic ecologybenthic macrofaunaBlack DrumPogonias cromisstable isotopesTextBreaux, Natasha Johnson