Graduation date: 1967

Graduation date: 1987

The benthic microalgae of sediments of the two tidal flats in Yaquina Bay, Oregon were investigated to determine the environmental factors limiting the abundance and the horizontal and vertical distribution of these organisms. The Southbeach tidal flat which is under the marine realm of deposition consists of fine to medium grained sand. The Sally's Bend tidal flat is under the fluviatile realm of deposition and consists of silt. Measurements were made of interstitial temperatures, movements of sand, turbidity, pH, salinity, depth of light penetration through the sediments, and the water content of the substrate. Samples of the benthic microalgal community were collected by using a piston corer. Sections of the cores were used for estimating the biomass: (1) by making direct counts of live microalgae, (2) by estimating chlorophyll a concentration and (3) by measuring ash-free dry weight. The greatest biomass of microalgae was found to be in cores from the lower intertidal zone while cores from the upper intertidal zone had the lowest biomass. This distribution probably results from the greater fluctuations in temperature, salinity, water content, and oxygen content, which are more variable in the upper intertidal zone. The greater biomass in cores from the lower intertidal zone may be the result of less fluctuation in environmental factors as well as the fact that this area is exposed to nutrient-laden water for longer periods of time than the upper intertidal zone. The greatest biomass of microalgae was found in the upper centimeter of cores collected at all levels of the intertidal zone, because light can penetrate no more than a few millimeters through sediment. Occurrence of algae below the photic zone is thought to result from vertical migration, sedimentation, or the activity of burrowing animals. It was found that the Southbeach tidal flat had a significantly greater biomass than Sally's Bend at all intertidal levels and in the various layers of the cores. This was attributed to differences in environmental conditions peculiar to each tidal flat which is the result of the hydrography of the bay. Estimates of the rates of potential gross production were made using a Gilson Differential Respirometer. The community from the Southbeach tidal flat had a greater potential gross rate of production than the Sally's Bend community. This was partially the result of high rates of bacterial respiration in cores from the Sally's Bend tidal flat. This tidal flat had significantly greater amounts of organic matter than Southbeach and the abundance of bacteria in sediment is related to the amount of organic matter. Measurements of the concentrations of chlorophyll a were corrected for the percentage of pheophytin present. Significantly greater amounts of pheophytin were found in cores from the Sally's Bend tidal flat which probably resulted from the large amounts of allochthonous detrital chlorophyll deposited in these sediments. The microflora consisted almost exclusively of diatoms. One hundred and fifty-four species and varieties were identified. Most of the species found in the lower intertidal zone were found in the mid and upper intertidal zones as well. Many of the species identified have never been reported from Oregon prior to this investigation. / Graduation date: 1969

Graduation date: 1987