Graduate Thesis Or Dissertation

Salinity as a factor controlling the distribution of benthic estuarine diatoms

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  • A two phase investigation was undertaken in an attempt to determine the effects of variations in salinity on the distribution of benthic estuarine diatoms. The estuary studied was that of the Yaquina River which originates in the Coast Range of western Oregon and discharges into the Pacific Ocean at the town of Newport, Oregon. The first phase involved periodic collection of samples of benthic diatoms at ten stations along a transect at the water's edge at low tide extending from salt water to fresh water, a distance of 20 miles. Permanent microscope slides were prepared and counts of 200 valves on each slide were made. The percentage of this total represented by each taxon was taken to be the relative abundance. The six most abundant species were selected and their relative abundances graphed. Synedra tabulata was found throughout the estuary but was most abundant at the lower three stations. Navicula tripunctata var. schizonemoides was found at the lower six stations, Melosira moniliformis was found at all stations and experienced a large increase in August, 1968. It is conjectured that the presence of this large crop of M. moniliformis might explain the decrease in relative abundance of several of the other taxa at this same time. Navicula gregaria was fairly well distributed above the lower two stations. N. comoides did not occur above the fourth station, but was found almost entirely in the lower estuary. N. viridula var. avenacea had a very limited distribution, being found in abundance only at the fifth, sixth and seventh stations. This first phase of the research also included measurement of environmental factors. Temperature of the sediment surface, salinity and light intensity data are presented. The second phase of the research involved isolation and culture of some strains of benthic diatoms, and performance of physiological experiments on these cultures. Six strains of one species of Amphora and one strain of another species of Amphora were obtained in culture and were examined under different combinations of salinity and light intensity in a Gilson Differential Respirometer. These particular strains of diatoms were relatively insensitive to variations in salinity but generally showed a decrease in photosynthetic production in fresh water. Zero light intensity caused a big decrease, as expected, and two strains showed a definite stimulation by the combination of highest salinity (30 parts per thousand) and highest light intensity (approximately 400 f.c.). The distribution of diatoms is related to variations in the environ:mental conditions of the estuary but a very complex interaction of all of these factors controls distribution.
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