EFFECTS OF TWO WAYS OF PRODUCTION
ENHANCEMENTS DUE TO SEASONAL SEA ICE ON TO THB MARINE ECOSYSTEM AT HIGHER LATITUDES
Masayuki Mac Takahashi*
University of Tokyo, Komaba, Tokyo, Japan
1. Introduction
The Arctic Ocean is characterized with being covered by seasonal or permanent sea ice. Sea ice could give various influences onto algal productivity in the water. Possible major positive influences are (1) supplying attaching substratum as well as giving other favourable condition for algae at the sea surface (ice algae), and (2) creating a stable water column condition for algal growth near the surface when ice melts (Smith and Sakshaug, 1990). These two influences could results in creating a unique ecosystem with high productivity in ice covered ocean.
A group of people in Japan are challenging to demonstrate such effects of seasonal sea ice onto marine ecosystem in the field of the 0khotsk Sea which is covered by seasonal sea ice in the southern end of the Arctic region. They have awarded a major research funds of 4 years from the Ministry of Education, Science, Culture and Sports, Japan from this fiscal year under the title of 'Sea-ice ecosystem: evaluation of the mechanism supporting its high productivity at higher latitudes'. Their research focus is set mainly on ice algae, particularly (l) to study mechanisms how to develop ice algal community including the development of seasonal sea ice, (2) to evaluate possible simulative effects of ice algae onto the entire ecosystem, and (3) to make quantitivative evaluation of the entire ecosystem having seasonal sea ice. These information could help to understand the ecosystem developped in the Arctic 0cean which has seasonal sea ice during a long period of time in the year as well as including possible comparison with the ecosystem having no seasonal sea ice.
Furthermore, it is urgent to understand the scientific nature of the 0khotsk Sea before starting active resource utilization because the Okhotsk Sea has long been kept away from major human influences, and is one of a few areas where there is no active resource utilization yet on the earth.
2. Advanced studies in the Bering Sea
Extensive studies on ecosystem structure and dynamics focussing on seasonal sea ice have been carried out in the Bering Sea and its neighborhood vicinity, apart of the Arctic region. Under the condition covered by seasonal sea ice, there occurs ice algal production from winter to spring followed by ice edge phytoplankton bloom when ice melts. Ice edge phtyoplankton bloom travels generally towards higher latitudes along with the receding ice edge.
Organisms living in seasonal sea ice ecosystem are then supplied foods directly or indirectly from ice algae and ice edge phtyoplankton bloom from the early part of year, which is extremely unique and is a possible major mechanism to support a productivie ecosystem at higher latitudes (Alexander, 1980). Actually it was observed that Alaskan pollock, Theragra chalcogramma, followed the ice edge and grew from juvenille to adults during the migratory travel following the receding ice edge(Walsh and McRoy, 1986).
3. Studies in the Okhotsk Sea
The Okhotsk Sea is also covered mostly of the sea by seasonal sea ice in the middle of winter. Sea ice thickness reaches nearly 150cm at the northern part of Sakhalin, about l.0m at the middle part, and 0,5m at the southern part. The most largest coverage of sea ice occurs in March in the 0khotok Sea. The large extension of sea ice
*Corresponding author's address: Masayuki Mac Takahashi,3-8-1 Komaba,, Meguro-ku, Tokyo
153-8902, Japan
e-mail: ctkmac@komaba,ecc.u.tokyo.ac.jp
