A Seasonal Diatom in a Frozen Wisconsin Lake¹

SUMMARY An extensive bloom of a stalked diatom, Cymbella sp., developed under the ice in Lake Wingra, a hard‐water lake in southern Wisconsin. The diatoms were attached to decomposing plants of Myriophyllum spicatum L. Uptake of H 14 CO 3 − showed the Cymbella to have an optimum temperature for carbon fixation of 25 C throughout the winter. Microscopic examination of samples taken from January through April showed Cymbella to dominate all other eucaryotic organisms. It is concluded that despite the fact this organism predominates in this winter habitat, it does not become optimally adapted to the temperature of its environment.