Benthic microalgae (BMA) living within the surface sediment of salt marshes are highly productive organisms that provide a significant proportion of organic carbon inputs into estuarine systems. BMA secrete extracellular carbohydrates in the form of low molecular weight carbohydrates and extracellular polymeric substances (EPS) as they migrate within the sediment. EPS plays an important role in the structure and function of BMA biofilms in shallow-water systems as EPS affects habitat structure, stabilizes the sediment, reduces sediment erosion, and is a carbon source for organisms. This study looked at the effect of nutrients and carbohydrate additions on BMA biomass, bacterial biomass, carbohydrate production, and glycosidase activity in the surface 5 mm of intertidal sediment in a subtropical salt marsh (Galveston Bay, Texas). Nitrogen and phosphorus were added to cores collected from the salt marsh and incubated in the lab over four days. Very little change was seen in the biomass of the benthic microalgae or in the different carbohydrate fractions with the added nutrients. The mean chlorophyll a concentration was 13 +/- 5 ug g-1 sediment, the mean saline extractable carbohydrate concentration was 237 +/- 113 ug g-1 sediment, and the mean EPS concentration was 48 +/- 25 ug g-1 sediment. The chlorophyll a and saline extractable carbohydrate concentrations initially decreased over the first 24 hours, but then increased over the rest of the experiment, indicating a possible species compositional shift in the BMA. With no major response with nutrient additions, it is likely that a different environmental factor is limiting for the growth of the benthic microalgae, and therefore the production of sEPS, in this salt marsh. A series of experiments was conducted in situ by adding glucose, alginic acid, and phosphorus to sediment within experimental plots. Samples were taken periodically over three to seven days to determine the biomass of the microbial community, enzyme activities and kinetics, and changes in the concentrations of several sediment carbohydrate pools. u-glucosidase activities (15 +/- 3 nmol g-1 h-1) were significantly higher than u-xylosidase (6 +/- 2 nmol g-1 h-1) and u-galactosidase (8 +/- 2 nmol g-1 h-1) activities within the sediment, and there was no suppression of u-glucosidase activity measured with the glucose addition. These data represent the first measurement of u- xylosidase and u-galactosidase activity in intertidal sediment dominated by BMA. Although preliminary experiments suggested a possible phosphorus limitation within the sediment, there was little change in the bacteria abundance or the benthic microalgae biomass when phosphorus was added in situ. This study begins to illustrate the dynamics of carbohydrate production and loss in this salt marsh, and the ability for the microbial community in the salt marshes of Galveston Bay to adjust to the nutrient and carbohydrate treatments.

Plankton communities are important members of the food web in coastal systems and are regulated by top-down and bottom-up controls. This study examined the influence of bottom-up controls, such as physicochemical factors, and top-down controls, such as predation, on the plankton communities in South Bay, Texas. Microalgal photopigments were ascertained by high-performance liquid chromatography (HPLC) to determine the relative abundances of major algal classes. Zooplankters were identified to the lowest possible taxon and enumerated. No spatial trends were observed for the physicochemical factors. The northern bay sections exhibited significantly higher phytoplankton and microphytobenthic diatom biomass, probably due to their proximity to the bay inlet. Copepod, gastropod veliger and brachyuran zoea abundances were also higher in this area, albeit insignificantly. The southern bay sections experienced significantly higher cyanobacterial, euglenophyte and chlorophyte biomass, and polychaete larval abundances. Total zooplankton and nauplii abundances were also higher in the southern areas, albeit insignificantly. Sampling the inaccessible areas of the bay in the future may reveal spatial variability among the physicochemical factors which could be influencing the distribution of plankton. Temporal variation for the physicochemical factors followed a typical trend for subtropical climates and influenced the seasonality of the plankton communities. Phytoplankton biomass peaked in February, August and October but these maximums were not significantly different from the other months sampled. Microphytobenthic biomass peaked during the summer months, while diatom biomass also peaked in February. Zooplankton abundances peaked in October, while nauplii and polychaete larvae also peaked in February. Relationships between wind speed, turbidity and the microalgal pigments were assessed to determine if wind-induced resuspension influenced the location of the major algal classes within the water column compared to the sediments. Wind speed and turbidity were directly related to each other, albeit insignificantly. Some phytoplankton and microphytobenthos were considered tychopelagic because wind-induced resuspension increased their biomass in the water column compared to the sediments. The physicochemical factors exerted bottom-up control of plankton community dynamics in this study, while top-down controls, such as predation, require further investigation. Future studies should focus on which of these controls have more influence on plankton community dynamics in South Bay.

The Avon-Heathcote Estuary is of significant value to Christchurch due to its high productivity, biotic diversity, proximity to the city, and its cultural, recreational and aesthetic qualities. Nonetheless, it has been subjected to decades of degradation from sewage wastewater discharges and encroaching urban development. The result was a eutrophied estuary, high in nitrogen, affected by large blooms of nuisance macroalgae and covered by degraded sediments. In March 2010, treated wastewater was diverted from the estuary to a site 3 km offshore. This quickly reduced water nitrogen by 90% within the estuary and, within months, there was reduced production of macroalgae. However, a series of earthquakes beginning in September 2010 brought massive changes: tilting of the estuary, changes in channels and water flow, and a huge influx of liquefied sediments that covered up to 65% of the estuary floor. Water nitrogen increased due to damage to sewage infrastructure and the diversion pipeline being turned off. Together, these drastically altered the estuarine ecosystem. My study involves three laboratory and five in situ experiments that investigate the base of the food chain and responses of benthic microalgae to earthquake-driven sediment and nutrient changes. It was predicted that the new sediments would be coarser and less contaminated with organic matter and nutrients than the old sediments, would have decreased microalgal biomass, and would prevent invertebrate grazing and bioturbation activities. It was believed that microalgal biomass would become similar across new and old sediments types as the unstable new sediments were resuspended and distributed over the old sediments. Contact cores of the sediment were taken at three sites, across a eutrophication gradient, monthly from September 2011 to March 2012. Extracted chlorophyll a pigments showed that microalgal biomass was generally lower on new liquefied sediments compared to old sediments, although there was considerable site to site variation, with the highly eutrophic sites being the most affected by the emergence of the new sediments. Grazer experiments showed that invertebrates had both positive and negative site-specific effects on microalgal biomass depending on their identity. At one site, new sediments facilitated grazing by Amphibola crenata, whereas at another site, new sediments did not alter the direct and indirect effects of invertebrates (Nicon aestuariensis, Macropthalmus hirtipes, and A. crenata) on microalgae. From nutrient addition experiments it was clear that benthic microalgae were able to use nutrients from within both old and new sediments equally. This implied that microalgae were reducing legacy nutrients in both sediments, and that they are an important buffer against eutrophication. Therefore, in tandem with the wastewater diversion, they could underpin much of the recovery of the estuary. Overall, the new sediments were less favourable for benthic microalgal growth and recolonisation, but were less contaminated than old sediments at highly eutrophic sites. Because the new sediments were less contaminated than the old sediments, they could help return the estuary to a noneutrophic state. However, if the new sediments, which are less favourable for microalgal growth, disperse over the old sediments at highly eutrophic sites, they could become contaminated and interfere with estuarine recovery. Therefore, recovery of microalgal communities and the estuary was expected to be generally long, but variable and site-specific, with the least eutrophic sites recovering quickly, and the most eutrophic sites taking years to return to a pre-earthquake and non-eutrophied state. changes in channels and water flow, and a huge influx of liquefied sediments that covered up to 65% of the estuary floor. Water nitrogen increased due to damage to sewage infrastructure and the diversion pipeline being turned off. Together, these drastically altered the estuarine ecosystem. My study involves three laboratory and five in situ experiments that investigate the base of the food chain and responses of benthic microalgae to earthquake-driven sedimen tand nutrient changes. It was predicted that the new sediments would be coarser and less contaminated with organic matter and nutrients than the old sediments, would have decreased microalgal biomass, and would prevent invertebrate grazing and bioturbation activities. It was believed that microalgal biomass would become similar across new and old sediments types as the unstable new sediments were resuspended and distributed over the old sediments. Contact cores of the sediment were taken at three sites, across a eutrophication gradient, monthly from September 2011 to March 2012. Extracted chlorophyll a pigments showed that microalgal biomass was generally lower on new liquefied sediments compared to old sediments, although there was considerable site to site variation, with the highly eutrophic sites being the most affected by the emergence of the new sediments. Grazer experiments showed that invertebrates had both positive and negative site-specific effects on microalgal biomass depending on their identity. At one site, new sediments facilitated grazing by Amphibola crenata, whereas at another site, new sediments did not alter the direct and indirect effects of invertebrates (Nicon aestuariensis, Macropthalmus hirtipes, and A. crenata) on microalgae. From nutrient addition experiments it was clear that benthic microalgae were able to use nutrients from within both old and new sediments equally. This implied that microalgae were reducing legacy nutrients in both sediments, and that they are

Benthic microalgal community composition on an ephemerally submerged sandflat at East Beach, Galveston Island, Texas was studied to determine the spatial and temporal variability of total biomass and community composition and its responses to experimental manipulations of two environmental factors (salinity and nutrients). Four field studies were conducted between August 2004 and February 2005. The community consisted of two major algal groups, diatoms, and cyanobacteria with two less abundant groups, green algae, and phototrophic bacteria. Spatial variability showed that patch sizes of 12 - 25 m were detected over larger scales with smaller scale (cm) patches of approximately 28 - 201 cm^-2 contained within the larger patches. The second study examined the spatio-temporal variability of BMA over a 21-month period in a 1,000 m^2 area. Sampling location and date explained a significant amount of the variability in the abundances of algal groups, which were positively correlated with the water content of the sediments and negatively correlated with temperature (sediment and water). All of the algal groups showed a seasonal pattern with higher abundances measured in the winter months and lower abundances found during the summer. BMA biomass (100 mg Chl a m^-2 or greater) maxima occurred at temperatures less than 22 degrees C and sediment water content greater than 15% (g water g sediment^-1). BMA response to different salinities and nutrient (N+P) amended sediments was assessed in four bioassays conducted over a 6-month period (Aug. 2004, Oct. 2004, Dec. 2004, and Feb. 2005). In the salinity study, the treatments that were either 100% or partially diluted with deionized water had the lowest BMA biomass over all. Chlorophyll a and fucoxanthin were significantly affected by salinity with higher abundances found in salinities that averaged 15 with a preference for salinities greater than 22. Chlorophyll b was affected by salinity with higher abundances measured in the treatments with lowest salinity (DL and DI); and was affected by the time of year. This would suggest that this algal group prefers an environment with salinity less than 2 but can easily adapt to environments with higher salinities. BMA abundances were not significantly affected by the nutrient amended sediment, but were significantly affected by stations with higher water content, and during the cooler months (Dec. 2004 and Feb. 2005).