Primary production and organic carbon flow in thepolar ocean ecosystems

We are focusing our efforts on achieving a better understanding of primary production and its utilization by higher trophs in polar ecosystems in relation to environmental conditions. In the fast ice area around the Japanese Antarctic station, Syowa (69°00'S, 39°35'E ), under-ice observation was carried out to describe seasonal variabilities in the ice algal community and its dependent zooplankters in a three-year program. The importance of ice algae to ice-associated copepod, Paralabidocera antarctica, and their link to nototheniid fish, Pagothenia borckgrevinki , were demonstrated. The development and application of automated measuring and sample collection systems for monitoring year-to-year variations of primary production have been achieved. On board the Japanese icebreaker, Shirase, biological and physical parameters, including chlorophyll concentration and optical plankton counts in the surface water, have been collected and published every year. A remote sensing technique is also utilized for obtaining temporal-spacial variabilities of primary production in polar waters. Mooring buoy systems with sediment traps were deployed for long-term observation in the Southern Ocean and Arctic waters to study marine production systems in lower trophic levels in ice-covered waters.

It is estimated that annual primary production south of the Antarctic Convergence is around 610 million tons. This large amount of phytoplankton serves to maintain the large amount and variety of zooplankton, e.g. Antarctic krill. The Adelie penguin is one of the most numerous penguins in Antarctica, with 2.5 million breeding pairs. They consume a large amount of Antarctic krill, and play an important role in the marine ecosystem in the sea-ice zone. It appears that the distribution of sea-ice affects the distribution of krill, which in turn affects the penguins' traveling and foraging activities. To assess the effects of sea-ice on the foraging performance of Adelie penguins, we attached a depth data logger to penguins at Hukuro Cove, Lützow-Holm Bay near Syowa Station, where fast sea-ice remains throughout the summer. A certain dive profile was recognized, which could be attributed to sea-ice (Fig.1). These results will be compared with other years and with other areas, Davis, Dumont d' Urville and so on, where fast sea-ice disappears during the summer.

Recent studies of diving animals have revealed their unexpected ability to accomplish frequent deep dives. For example, king penguins usually dive deeper than 300m and longer than 7 min (Fig.2). Numerous deep divers, penguins, seals and cetaceans apparently depend on prey scattered in the deep. They play an important role in the Southern Ocean ecosystems because of their large populations, wide distribution, and high energy demands. This suggests that a large amount of prey organisms like squids and myctophid fishes are distributed in the mesopelagic zone. However, the biomass of these prey organisms is still unknown. How do the deep pursuit divers catch their prey in deep sea communities? To answer this question, we are developing micro data loggers which can record several parameters (depth, temperature, light intensity, swim speed, etc.) with high frequency sampling intervals. These loggers are attached to marine animals to obtain information about their behavior, physiological condition and the environment under water.

The population dynamics of the Adelie penguin near Syowa Station have been monitored continuously for 15 years and will continue to be monitored in an effort to understand the long-term fluctuations of population in relation to environmental conditions.

This group promotes taxonomical, ecological and physiological studies of plants and animals in ice-free areas near Syowa Station. Since the international program BIOTAS (Biological Investigation of Terrestrial Antarctic Systems) was initiated in 1986 by SCAR, comprehensive studies on the structure and function of Antarctic terrestrial ecosystems have been carried out in the Yukidori Valley, Langhovde, with special emphasis on mosses, lichens, freshwater algae and invertebrates. Soil microorganisms and vegetation in the valley are monitored in relation to temporal and long-term changes in the local and global environment, using open-top chambers installed in moss colonies (Fig.1).

The origin and colonization processes of flora and fauna are studied to learn about the ecosystems in harsh polar environments. Taxonomical and reproductive studies of such main elements of the ecosystem as algae, mosses, lichens and invertebrates are carried out. Taxonomical investigation of such small animals as mites, nematodes, tardigrades and collembola is undertaken. Ecological study of mites is also conducted along the Yukidori Valley. Their habitat preference is identified with respect to moisture, food and temperature tolerance. These animals as well as soil bacteria are important decomposers in the Antarctic terrestrial ecosystem, so studies of the energy budget of this group will continue.

The biological, chemical and physical characteristics of the fresh-water lakes near Syowa Station are investigated. Water temperature, dissolved oxygen, conductivity, pH, depth, and transparency are measured, and net-plankton and benthic algal mats are analyzed. In particular, curious tower-like structures composed of mosses rising from the algal mat on the lake bottoms are investigated (Fig.2,3).