Gable, George M., IV (2007-08). Spatio-temporal patterns of biophysical parameters in a microtidal, bar-built, subtropical estuary of the Gulf of Mexico. Master's Thesis.
Plankton communities are influenced, in part, by water exchange with adjacent
estuarine and oceanic ecosystems. Reduced advective transport through tidal passes or
with adjacent bay systems can affect chemical processes and biological interactions,
such as nutrient cycling, phytoplankton abundance and productivity, community
respiration, and zooplankton biovolume. The most threatened estuarine ecosystems are
shallow, bar-built, microtidal estuaries with small water volumes and restricted
connections through tidal passes and other water exchange points.
This research explored spatio-temporal trends in plankton communities and the
physicochemical environment in Mesquite Bay, Texas a microtidal, bar-built,
subtropical estuary in the Gulf of Mexico. This research couples sampling at fixedstations
for multiple physical and biological parameters with high-resolution spatial
mapping of physicochemical parameters.
Spatial trends were less in magnitude and affected fewer parameters in fixed station
and spatial data. Two dimensional ordination plots indicated spatial heterogeneity with a
more pronounced temporal trend affecting parameters including temperature, salinity as a function of inflow timing, and seasonal wind direction affecting primary production
and zooplankton biovolume.
Temperature was positively correlated with gross production and respiration rates
during spring and late summer with sporadic positive and negative correlations with
phytoplankton biomass. The timing and magnitude of freshwater inflow affected
various physicochemical and biological parameters. Higher than 71-year inflow rates
resulted in low salinity system wide, with spatial heterogeneity increasing over the
course of the study, which was confirmed by spatial maps. Additionally, high inflow
rates led to two periods of increased inorganic nutrients and dissolved organic matter.
Low salinity periods coincided with persistence of higher turbidity, likely because of
decreased sediment flocculation. Gross production was low at this time, and likely from
light limitation. Additionally, wind magnitude and direction created spatial
heterogeneity in turbidity levels and phytoplankton biomass. Zooplankton biovolume
was highest during spring and late summer with high species diversity in total rotifers.
Copepod biovolume and phytoplankton biomass were positively correlated. Other
zooplankton taxonomic groups exhibited variable correlations with phytoplankton
biomass and other taxonomic groups. Further long-term studies are needed to determine
interactions of various components of trophic food-webs and account for interannual
variability in all system parameters.