under-ice filamentous algae

McMurdo Sound is continuously dark for four months in the winter and continually light for four months in the summer; these are separated by two-month transition periods in which the light increases or decreases by twenty minutes per day [1]. To the human eye, lighting can be dim under the sea ice. The sea ice reduces light as does its overlying snow cover and the organisms living on its underside. At noon during McMurdo Sound summer, the sea ice undersurface receives less than 1% of the sun's irradiance [2]. This isn't much light for algae and diatoms to use for their photosynthesis yet they have adapted. Called cryophiles for their ice lifestyle, they live in low light intensity and make a significant contribution to primary productivity under the ice [2].


The fish Pagothenia borchgrevinki is perched on a grounded iceberg just south of Cape Evans on Ross Island. The surface of the ice is covered with a sea ice microbial community comprised of algae, diatoms, bacteria and protozoans; the brown coloration is due to photosynthetic pigments. Crustaceans and molluscan pteropods graze on the microalgae and fish prey on the crustaceans.

1: Science 238:1285-1288, 1987; 2: Polar Biology 2:171-177, 1983

Text ©Peter Brueggeman. Photographs © Canadian Museum of Nature (Kathleen Conlan) & Norbert Wu. Photographs may not be used in any form without the express written permission of Canadian Museum of Nature (Kathleen Conlan) and Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?