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Distributional patterns and taxonomic structure of diatom assemblages in Netarts Bay, Oregon

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  • Epiphytic, planktonic and benthic diatom assemblages were investigated in Netarts Bay, Oregon. Samples were collected for a one-year period from February 1980 to March 1981. A planktonic flora was observed only during periods of offshore enrichment when marine neritic species were abundant and were transported into the bay by tidal currents. Multivariate analyses demonstrated that epiphytic and benthic assemblages were distinct, with relatively little overlap in distribution of dominant taxa. The dynamics of the epiphyte assemblage were seasonal in nature, presumably related to the growth dynamics of the host plant Zostera marina) as well as to seasonal changes in the physical environment. Intertidal exposure gradients exerted little influence on the distribution of dominant epiphyte taxa. In contrast to the epiphytic flora, dominant benthic taxa demonstrated little seasonal variation in relative abundance. The effects of intertidal exposure gradients on benthic diatoms were dependent on interactions with different sediment types. Benthic taxa in silty sediments were virtually unaffected by intertidal gradients while many taxa in sandy sediments had marked intertidal preferences. Most of the variation in the distribution and relative abundances of benthic taxa could be explained by the physical properties of the sediment, especially mean particle diameter, sediment organic content, and the degree of sediment sorting.
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