Date of Award

11-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

Abstract

Freshwater wetlands in the Lower Rio Grande Valley of Texas are locally known as resacas. Resacas are remnants of the Rio Grande River channel that were cut off by sedimentation and erosion of river banks. Many are maintained as permanent wetlands through intermittent water pumping from the river; and provide valuable habitat for fish, invertebrates, migratory birds and a diverse floral community in the semi-arid environment of South Texas. Three resacas in different stages of ecosystem development were studied, including one from day zero after re-flooding. The objectives were to document the colonization process of the re-flooded resaca and the macroinvertebrate community of all three sites to differentiate successional stages of the studied resacas. Two invertebrate collection methods were used, benthic corer and sweep net, in order to gather a representative sample from the entire community. Results indicated that environmental factors (i.e. water, sediment) varied little between resacas, but there were significant differences in the benthic and water column invertebrate communities among the sites studied. The most developed site exhibited the lowest diversity and richness, and the highest dominance. The intermediate site exhibited the greatest diversity and richness, and a low level of dominance. The new site fell between the other two, but was most similar to the intermediate site. Composition of the functional feeding groups did not follow expected trends within this community, but is still a useful metric for differentiating the study sites, particularly the predator and scraper taxa. The invertebrate community in the studied resacas did not follow successional trends that were expected based on other studies and the community was strongly influenced by the presence of an invasive gastropod. Based on the results of this baseline study, the invertebrate community may be useful in discriminating between successional stages of resacas.

Granting Institution

University of Texas Brownsville

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