Graduate Thesis Or Dissertation
 

The distribution of intertidal diatoms associated with the sediments of Yaquina Estuary, Oregon

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  • Sediment samples were collected from eight sampling sites along the Yaquina Estuary, Oregon from Yaquina Bay to Elk City near the head of the estuary. Samples were collected in November 1973, February 1974, May 1974 and August 1974 from two or three intertidal levels depending on the magnitude of the intertidal area exposed at low tide. Concurrent sediment and water samples were obtained for the determination of water temperature, salinity, sediment size, and percentage of organic carbon and cabonate in each sample. Incident light and exposure period data were obtained for the sampling year. A total of 36,564 diatoms identified and counted in 71 samples was separated into 390 taxa (species or varieties). Of the 390 taxa, 31%, representing 30% of the total cell count, could not be identified from available literature. The relative abundance values of the taxa were utilized for the comparisons of several community composition parameters (the Information measure, Simpson's diversity index, redundancy, niche breadth, and a measure of similarity) which were used for comparisons of spatial and temporal distributions of sediment-associated diatom assemblages within the estuary. Multivariate analyses (clustering, disciminant analysis, principal components, canonical correlation) of species and environmental data were employed to analyze the distribution of sediment-associated diatom assemblages relative to the sampling strategy and to environmental gradients. The distribution of sediment-associated diatoms in Yaquina Estuary was regulated primarily by mean salinity and characteristics of the sediment. Above Yaquina Bay the prominent taxa exhibited overlapping distributions along the salinity gradient to a location in brackish water where the mean salinity was approximately 5°/oo. Here, a relatively sharp discontinuity in the diatom flora existed which appeared to be the product of the biochemical and biophysical mechanisms involved in osmotic regulation of mesohalobian and oligohalobian assemblages. Relatively large disparities in the structure of sediment-associated diatom assemblages were found within relatively small local areas of Yaquina Bay. These differences were attributed to the properties of the sediment, Responses of the diatom assemblages to light intensity, temperature and exposure to intertidal emergence were not obvious. Approximately one-half of the numerical variation in the diatom flora apparently was related to factors other than the physical and chemical variables considered in this study. Comparisons of previous distributional surveys in Yaquina Estuary indicated that the diatom flora associated with the sediments was dissimilar in species composition to proximal epilithic, epiphytic and planktonic diatom assemblages. Species diversity was generally high throughout the intertidal sediments, irrespective of tidal height and season, while redundancy was generally low. High diversity values may represent contamination of samples, behavioral-physiological adaptations of the sediment flora, or the spatial heterogeneity of intertidal sediments.
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