Thesis Defense Seminar - Melanie Ponce

MARINE BIOLOGY PROGRAM
DEPARTMENT OF LIFE SCIENCES
TEXAS A&M UNIVERSITY-CORPUS CHRISTI

TITLE: Assessing spatial and temporal variability in benthic invertebrate communities in Texas beaches

GRADUATE COMMITTEE: Dr. Jennifer Pollack (advisor), Dr. Kim Withers, Dr. Terry Palmer

ABSTRACT
Beaches are ecologically and economically important coastal habitats. Intertidal zones within these beaches host dense concentrations of benthic invertebrates that support productive foraging grounds for shorebirds, crabs, and fish. Due to their relatively low motility, long lifespan, and specific habitat associations, benthic invertebrates serve as useful indicators of environmental changes within those habitats, including beaches. This study evaluated temporal and spatial variations in benthic invertebrate communities inhabiting the intertidal zone of beaches on the upper Texas coast and assessed key environmental factors influencing these communities, including sediment type, water quality, and beach profile dynamics. Results indicate that the northern beaches had higher benthic invertebrate abundance than the mid-coast beaches, with abundance increasing during warmer months. Benthic invertebrate abundance in northern and mid-coast beaches was positively influenced by temperature and negatively by dissolved oxygen. Biomass and diversity were similar between these regions, with biomass positively correlated with temperature and negatively with dissolved oxygen. In northern beaches, diversity was positively influenced by temperature, salinity, beach height, and beach width, but negatively associated with pH, water level, turbidity, and dissolved oxygen. In mid-coast beaches, diversity was positively influenced by temperature and negatively by dissolved oxygen. Turbidity and dissolved oxygen had the strongest positive association with benthic invertebrate community composition at northern beaches, whereas sand and beach width were the strongest predictors at mid-coast beaches. Northern beaches had higher abundance and diversity of birds. Sediments in northern beaches were composed solely of sand, whereas mid-coast beaches had a mixture of sand, silt, and clay. Sargent Beach, located in the mid-coast region, showed the highest percentage of clay, with proportions increasing over the sampling period. These findings highlight distinct patterns in benthic invertebrate communities along the Texas coast, with higher abundance and diversity at northern beaches characterized by sandy substrates, compared to more varied sediment composition at mid-coast beaches that includes silt and clay. The greater diversity of birds at northern beaches may be linked to abundance and diversity of benthic invertebrates in these areas. The spatiotemporal variability in benthic invertebrate communities, influenced by environmental factors such as temperature, dissolved oxygen, and sediment type, emphasizes the importance of establishing ecological baselines to effectively monitor and assess responses to future coastal disturbances.