EPIBENTHIC ALGAL PRODUCTIVITY AND EXTRACELLULAR RELEASE OF DISSOLVED ORGANIC COMPOUNDS IN A TEXAS COASTAL MARSH
HALL, SHELLY LOU
Doctor of Philosophy
The bluegreen algal community of a Texas coastal marsh was studied in order to estimate annual productivity and extracellular release of dissolved organic compounds. The effects of various environmental factors on these processes were also investigated. Productivity of the algal mat was highest in the summer, with the lowest rates of carbon fixation occurring in December. Annual productivity was estimated to be 71.04 g C m('-2), approximately 10% of the net aerial productivity of the grass canopy. While this may appear to be a minor contribution in terms of magnitude, the algal material is directly available to consumers while the grasses must decay before assimilation is possible. Of the environmental parameters studied, temperature had the greatest effect on productivity. The rate of carbon fixation was also affected by light intensity and salinity, however factors which modify the amount of biomass present such as grazing and flooding are more important in determining annual productivity. The pattern of ('14)C incorporation into various intracellular fractions (low molecular weight metabolites, polysaccharide, and protein) was useful for further assessment of environmental effects. For example, changes in the relative incorporation of label into the protein fraction were evident during moderately unfavorable conditions when the rate of carbon fixation was apparently unaffected. The filamentous bluegreen algae studied released an average of 3.7% of their photoassimilated carbon into the environment. Annual release was estimated to be 2.25 g C m('-2). Increasing extracellular release accompanied greater rates of carbon fixation and those environmental factors which influenced productivity had a similar effect on excretion. However, fluctuations in the water potential of the external environment were very important in determining the rate of extracellular release; high salinity or low soil moisture were responsible for high rates of excretion. Mannitol and trehalose were identified as the most commonly released compounds, with occasional evidence for the release of glucose and sucrose. The presence of mannitol, in particular, suggests that in natural situations extracellular release of organic compounds can function in osmotic adjustment.