| Summary: | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Science from Texas A&M University-Corpus Christi in Corpus Christi, Texas. Mollusks are an abundant species rich phylum within the animal kingdom. Over 130,00 species have been documented, and the Texas Gulf Coast is home to a large portion of these species. Many of these species reside within Texas Estuaries that experience differing freshwater inflow patterns. Freshwater inflow changes can alter estuarine dynamics such as salinity, nutrients, and some biological communities. Many mollusks species’ survival and growth rely on freshwater inflow for nutrients for reproduction and survival and are thus suitable bioindicators of freshwater inflow effects within estuaries. Existing mollusk and salinity data from 1987 - 2019 were used, and estuaries compared include Lavaca-Colorado, Guadalupe, Mission-Aransas, Nueces, and Baffin Bay-Upper Laguna Madre. Current environmental inflow standards were determined using Rangia cuneata, a brackish water clam found only in Guadalupe Estuary, as a bioindicator. In addition to Rangia cuneata, other dominant species with the highest frequency along all estuaries such as Mulinia lateralis, Nuculana acuta, Mysella planulata, and Macoma mitchelli were examined. were also examined as bioindicators. There were distinct differences in community structure along the salinity gradient on The Texas Coast. Laguna Madre was greatly different compared to other estuarine systems because of being seagrass habitat in comparison to other systems that were bay-bottom mud habitat. Laguna Madre also has the highest salinity leading to a diverse community of mollusks. High inflow systems, such as Guadalupe and Lavaca-Colorado, resulted in high abundance of opportunistic species such as Mulinia lateralis, and in contrast there was a higher mollusk diversity found in estuarine systems with higher salinity. All the dominant species responded to freshwater inflow with reproductive ...
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