Ecosystem resilience following salinity change in a hypersaline estuary

Abstract

Salinity variability can act as a disturbance to communities in estuarine systems. Climate models predict changes in precipitation patterns will increase future hydrological variability, particularly in the southwestern United States. This study used infaunal community characterization, stomach content, and stable isotope analyses to evaluate the functioning of an estuarine food web over a range of wet and dry conditions. Baffin Bay is a predominantly hypersaline system in the semi-arid region of South Texas, USA supporting large populations of Pogonias cromis, black drum, a commercially important benthic predator. Salinity was the best predictor of changes in benthic macrofauna biomass, abundance, and diversity in Baffin Bay. Isotopic analyses of muscle tissues indicate that black drum use resources, particularly deposit-feeding benthic macrofauna, from both Baffin Bay and an adjacent system under normal estuarine salinity (≤35) conditions, but are more constrained to Baffin Bay under hypersaline (>35) conditions. This spatial restriction may be due to the energetic cost of osmotic regulation in hypersaline conditions, which can limit movement of euryhaline fish. Understanding the impacts of salinity change on benthic prey availability and trophic interaction dynamics is critical to determining ecosystem-scale effects of salinity variability.