Date of Award

5-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

Efforts to restore Bahia Grande, a 2630 hectare, historically sea grass dominated playa lake, are currently underway and describing its current ecological status is critical to recommending any future physical manipulations to the immense basin. A benthic community based study was conducted on three estuaries in Cameron County, Texas (2012 to 2013) in order to compare the polychaete community dynamics and ecosystem productivity rates of the restored basin to that of two older adjacent reference sites (i.e. South Bay and San Martin Lake) in an effort to gauge system status. All three sites were once contiguous with the Lower Laguna Madre and remain in close proximity yet differ in degree of anthropogenic disturbances and biological and physical environments. Benthic core sediment samples and water quality parameters were retrieved quarterly along with monthly aquatic and ambient temperature and oxygen data. Additionally, data loggers were deployed at each site two weeks per month for one year. Net Ecosystem Metabolism (NEM) rates were determined by generating diel oxygen curves adjusted for wind-diffusion. PERMANOVA analysis of abundance data revealed significant difference by site, quarter, and by an interaction between site and quarter. Further investigation of assemblages using SIMPER revealed different species were driving the site dissimilarities. Physical differences between the systems were largely due to varying levels of salinity and dissolved oxygen as exhibited by PCA ordination. PERMDISP revealed that Bahia Grande undergoes higher temporal variability than the reference sites, which is considered to be an indication of instability. Bahia Grande appears to be trending similarly in terms of ecosystem metabolism however, the basin is functioning differently in terms of production and respiration. Bahia Grande currently hosts a community that is temporally variable and highly dominant with low diversity, and low productivity. Recommendations supporting future manipulations to increase tidal flow and freshwater input, thus lowering hydraulic residence time and potentially increasing recruitment are strongly suggested based on the findings of this study.

Granting Institution

University of Texas Brownsville

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