| Summary: | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Biology. Estuarine ecosystems can experience extended periods of salinity and temperature stress. In the South Texas region of the northwest Gulf of Mexico (GoM), climate models and current trends support increased temperatures, prolonged droughts, and increased storm severity. It is therefore imperative to assess how climate stress will impact South Texas estuarine ecosystems. Coastal lagoons are particularly vulnerable to disturbance, and the hypersaline Baffin Bay and Upper Laguna Madre Complex is a ‘hotspot’ of environmental change. In this dissertation, factors contributing to hypersaline microbial community dynamics in a hypersaline creek were assessed in three stand-alone research projects: 1) a short-term 2-month study of microbial community dynamics following a flood event, 2) a long-term 18-month study of microbial community dynamics that included flood and freeze events, and 3) a targeted study of wildlife connectivity (Mexican free-tailed bats) to microbial community dynamics and eutrophication. The short-term study revealed that flood events are disturbance events that cause pronounced shifts in microbial community structure. The long-term study revealed the hypersaline community was resilient to flood and freeze events. Additionally, whole genome sequencing of halophilic bacteria uncovered mechanisms of osmoregulation and heavy metal resistance. The targeted study revealed that bat guano is a source of dissolved organic carbon and potentially pathogenic bacteria. Severe heat coupled with severe flooding is anticipated to alter salinity regimes, increase osmotic stress, adversely impact ecosystem stability, and potentially restructure natural communities between drought and flood events. Climate stress will also affect the quality of riparian buffers and the wildlife inhabiting those buffers. A better understanding of microbial drought and flood resilience is critical to predicting ...
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