Page 35 - living-ice

Algae curtains
The light in the ocean diminishes with increasing depth. Even only two meters under sea ice covered by 20 cm of snow, the light can be more than 90 % lower than on the snow surface. Outside the shallow coastal areas of the Arctic Ocean, it is too deep for algae to grow on the seabed. Consequently, ice algae play an important role for animals that live in the water column and even for those on the seabed. An unusual example of such ice algae is Melosira arctica. This tiny unicellular diatom can form meter-long chains that hang from the bottom of the ice like curtains. When these algae chains detach from the ice oe, they sink quickly to the seabed and provide much needed food for hungry benthic organisms.
Arctic researchers have identi ed traces of ice algae in a whole range of ben- thic organisms such as brittle stars, clams and sea urchins. Some organisms eat the ice algae directly, while others eat animals that have eaten ice algae. It appears that some organisms even prefer ice algae to phytoplankton. Re- searchers believe the reason for this is that the ice algae represent healthy food with large stocks of nutritious compounds that contribute to the growth and reproduction of Arctic animals. These animals cannot produce these substances themselves.
PHOTO: Igor Melnikov, P.P. Shirshov Institute of Oceanology