Temperature effects on the valve structure of the bipolar diatoms Thalassiosira antarctica and Porosira glacialis

Summary

Clones of the bipolar diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grun.) Jørg. from both hemispheres grown at 4 and-1.5°C were noted to have morphological differences between the two temperatures that were not visible in the light microscope but evident in the scanning electron microscope. At the lower temperatures T. antarctica lost the occluded processes and the external tubes of the strutted processes but retained the external tube of the labiate process. P. glacialis lost all external tubes at-1.5°C. In both species, the foramina were greatly constricted at-1.5°C, in contrast to the open foramina at 4°C. Heterovalvate cells were found in both species, indicating a discrete change in valve structure rather than a slow, gradual change resulting in a continuum of variation.