Graduate Thesis Or Dissertation
 

Structure and productivity of marine benthic diatom communities in a laboratory model ecosystem

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  • Effects of light intensity, exposure to desiccation, reduced salinity, and thermal elevation on the functional and structural characteristics of marine benthic diatom communities were investigated in a laboratory model ecosystem and a respirometer chamber. Measurements of biomass (dry weight and ash-free dry weight) and chlorophyll a were made for each of the communities. Population studies were performed to determine community structure. Finally, photosynthetic rates of the communities at selected light intensities were determined in the respirometer for communities developed in experiments designed to test the effects of exposure to desiccation and variations in light intensity. Biomass accumulated most rapidly on substrates subjected to high light intensities, without exposure to desiccation. Under intertidal conditions, biomass accumulation was progressively greater with less exposure to desiccation. Organic material (ash-free dry weight) was greater on substrates from summer than winter experiments. Both reduced salinity and thermal elevation interacted with light to stimulate algal production, and mats of Melosira nummuloides developed rapidly and floated to the surface. Communities acclimated to different light intensities and periods of desiccation responded differently to various light intensities in the respirometer chamber. Substrates receiving little atmospheric exposure developed thicker layers of biomass permitting significantly higher rates of photosynthesis as light intensity increased. Generally, substrates developed at low light intensities attained a maximum photosynthetic rate at the lower light intensities in the respirometer, presumably because of an acclimation phenomenon. Community structure, as computed by the Shannon-Weaver information function, showed increasing diversity with increasing atmospheric exposure. During the summer experiment this was caused by an increase in the number of species, but in the winter experiment this was caused by a greater evenness of distribution of the species within the community. In the experiments designed to determine the effects of light intensity, diversity decreased with increasing light intensity during the summer, but the opposite pattern was observed in the winter. In both experiments the number of species decreased with progressively higher light intensities; evenness of species numbers in the summer decreased with increasing light intensity, but increased with increasing light intensity in the winter. Communities developed under conditions of reduced salinity or increased temperature showed decreasing diversity with increasing light intensity. This was due both to fewer species and an unevenness of species distribution. Results of these experiments demonstrate the potential of the laboratory model ecosystem as a tool for the investigation of simplified communities. It may be used to gain information that can supplement and help understand concurrent field observations.
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file details WulffBarryL1971.pdf 2017-08-17 Pubblico Scaricare