Roehrborn, Linda Rae (2006-12). Seasonal analysis of abiotic factors impacting phytoplankton assemblages in Offatts Bayou, Galveston, Texas. Master's Thesis. Thesis uri icon


  • The aim of this investigation in Offatts Bayou was to quantify natural shifts in
    distributions and abundances of algal groups and to examine spatio-temporal patterns of
    abiotic and biotic characteristics in the water column over a one year period. To
    accomplish this, hydrological and meteorological parameters were collected and
    phytoplankton biomass, community composition and chlorophyll a data were examined
    for significant relationships. Seasonal variations in water temperature, salinity,
    dissolved oxygen concentrations and pH levels, as well as wind effects, zooplankton
    grazing, light availability and hydrodynamic restriction were considered as the key
    controlling factors in phytoplankton dynamics in Offatts Bayou.
    Surface water samples and water column hydrological data were collected at
    eleven stations in the Offatts Bayou embayment on a regular basis (2 to 4 times per
    month), along with phytoplankton tows on a monthly basis. Spatial patterns of
    phytoplankton abundance generally reflected the degree of circulation in Offatts Bayou
    with higher abundances observed in the restricted areas and lower abundances in the
    well mixed regions. Temporally, diatom blooms became more prominent during winter, spring and autumn, which were characterized by cooler temperatures, less light
    availability, increased dissolved oxygen concentrations and reduced salinities than
    observed in summer. The most dominant diatoms were Guinardia delicatula, Ditylum
    brightwelli, Rhizosolenia setigera, Dactyliosolen fragillissimus and numerous
    Chaetoceros species. During summer, the waters of Offatts Bayou were warmer and
    more saline, which lead to the haptophyte, Corymbellus aureus, becoming the dominant
    taxa, with highest standing crops at the circulation restricted stations in Lake Madeline.
    While the results of this study support the importance of temperature, dissolved
    oxygen and pH as the critical controlling factors (p < 0.05) of phytoplankton biomass
    and diversity, it is clear that phytoplankton dynamics in Offatts Bayou must be viewed
    within the broader context of additional parameters such as salinity, stratification and
    wind effects. The progressively degrading conditions within Offatts Bayou emphasize
    the significance of studying and understanding the interrelationships of factors and
    mechanisms that influence phytoplankton dynamics. Long term monitoring of Offatts
    Bayou is essential for tracking, recording and assessing various human impacts to
    phytoplankton distribution, abundance, and productivity as well as impacts to higher
    trophic levels such as fish and humans.

publication date

  • December 2006