ARCTIC Quantitative Composition, Distribution, Community Structure and Standing Stock of

ABSTRACT. One hundred and ninety-six (196) species of microalgae were identified from the annual shore-fast sea ice samples collected from the Canadian Arctic between November and June in the years 1971 to 1978. The diatoms were represented by 189 species (21 centric and 168 pennate), the flagellates by three species, the dinoflagellates and chrysophytes by two species each. There were no blue-green algae. Species composi-tion and distribution are tabulated. The dominant species of the microalgal communities in the bottom of the ice different from those found elsewhere in the ice. The sea ice microalgal communities and standing stock started to develop in late fall at the time of ice formation. They grew very slowly through the winter months, exponentially increased in early spring, reached a peak just prior to the thaw period in late spring or early summer, and declined rapidly in summer as ice melting occurred. Standing stock was greatest at the bottom of the sea ice, where it was one to two orders of magnitude larger than in other parts of the ice column, and 50 to 500 times greater than in the phytoplankton in the underlying waters. The ice communities consisted mainly of diatoms with a great majority of pennate forms. Large numbers of species and cells of diatoms were found at th