Production　and 　Vertical 　Flux　of 　Ice 　Algae

Ecological role of ice algae inhabited at the bottom layer of sea ice is equivalent or more significant than phytoplankton found under the sea ice as a primary producer in the sea frozen during winter. Phytoplankton cell is incorporated into ice crystals as they form. These ice crystals develop through several different ice stages while algal cells remain scattered throughout the ice during winter. Their biomass stays low until the end of winter. As temprature increases brine starts draining and an active migration of cells occurs throughout the brine channels in the ice. Subsequently the algal cells become concentrated in the bottom few centimeters of ice. A rapid growth begins in response to increasing light levels and continues throughout the spring. During a melting period the ice algae are released into a water column underneath the disintegrated ice. As an example of coastal water frozen during the winter in Japanese water, Lake Saroma is chosen to compare the primary production by ice algae with one by phytoplankton. During the ice covered period the primary production by ice algae is predominant compare to one by phytoplankton while the primary producers are switched to phytoplankton and benthic algae during the rest of year. When the amount of annual primary production is considered, one by ice algae is appreciable. As mentioned above, the production processes are well studied for the ice algal community. However few studies concentrate the fate processes of the ice algal community in past. A direct or indirect grazing effect by zooplankton, a vertical transport through aggregation, and a seeding for the spring bloom of phytoplankton are included in the fate processes. An active grazing by zooplankton occurs but its contribution to the fate processes is insignificant quantitatively. Ice algae aggregate due to their biological, physical and chemical characteristics. Most ice algal cells are transferred rapidly as aggregates to the bottom. Algal cells left from this process act as a seed for the spring bloom of phytoplankton in a water column.