Lee, Hannah Alyssa (2017-05). Effects of Physical Disturbance on Phytoplankton Diversity and Community Composition in Galveston Bay, TX, during an Extreme Flooding Event. Master's Thesis.
Thesis
With climate change, future storm frequencies and intensities and El Nino events are expected to increase. These have the potential to cause flooding within the Galveston Bay (Texas) watershed as well as other locations. Increased rainfall can lead to changes in phytoplankton diversity, biomass and density in estuarine communities and cause phytoplankton community composition shifts. However, studies showing the specific physical drivers of these community composition changes are limited. In the spring of 2015, areas within the Galveston Bay watershed experienced extreme rainfall that caused this bay to receive unusually large amounts of freshwater inputs that lead to flooding. Wind speed, mean daily freshwater inflows, mean daily tide height and individual water quality parameters such as salinity, temperature, and dissolved oxygen were collected in order to examine their effects on phytoplankton diversity and community composition. Daily water samples were taken from lower Galveston Bay (29.31 N, -97.21 W) adjacent to the Gulf of Mexico. The phytoplankton in these samples were examined using an Imaging FlowCytobot in order to document community composition shifts down to lowest practical identification level. Temperature, freshwater inflows and salinity were the major physical drivers of phytoplankton community composition in Galveston Bay over the study period. In addition, during the flooding event, phytoplankton diversity, biovolume and abundance decreased. This event also corresponded with a decrease in dinoflagellate abundance and an increase in diatom abundance. It was found that during the transition between the flooding and end of the flooding event there was an increase in Myrionecta sp., suggesting an important predator- prey relationship after extreme floods in this system. The pre-flooding and post-flooding phytoplankton communities were primarily driven by temperature, indicating that they were more influenced by seasonal changes than the flooding event. Compared to previous studies, this approach has allowed us to link much finer scale community composition changes in Southern Galveston Bay, both temporally, through daily sampling, and taxonomically, through genus level taxonomic resolution, with physical parameters. This will be the first study looking at the effects of tide height and wind speed on phytoplankton in Galveston Bay. These novel results can help researchers have a better idea of how the physical changes that come with climate change can affect the base of the marine trophic web.
