LABORATORY STUDIES OF ASSEMBLAGES OF ATTACHED ESTUARINE DIATOMS

EFfects of light intensity, exposure to desiccation, salinity, and heated water on the vertical distribution and growth of populations of attached estuarine diatoms were studied in a laboratory model ecosystem. Of the 35 most abundant diatom taxa found in 36 samples from the laboratory system, all but 8 were also abundant in s‘amples obtained from Yaquina Bay and estuary. Vertical distribution of diatoms was more closely related to light intensity and period of exposure to desiccation in the summer experiments than in the winter experi-ments. A sudden, unseasonable decre,ase in salinity or increase in water temperature had a much greater effect on diatom assemblages exposed to 12,270 lux than on those that developed at either 1,030 or 4,710 lux; the most noticeable changes in community structure included a decrease in species diversity and a rapid growth of a population of Mebosiru nummuloides, a filamentous species. Primary productivity in diatom assemblages exposed to periods of desiccation was less under winter conditions than under corresponding conditions in summer. Prim,ary productivity in assemblages not exposed to desiccation was strongly affected by light intensity during both summer and winter experiments, and the ratio primary productivity: chlorophyll a was greater during winter than summer