Structure of the marine ecosystem of the Ross Sea, Antarctica —overview and synthesis of the results of a Japanese multidisciplinary study by Kaiyo-Maru and JARPA—

Abstract

A multidisciplinary marine ecosystem study in the Ross Sea region of the Antarctic was conducted in austral summer in 2004/05 as a Japanese national program. A fisheries research vessel, Kaiyo-Maru, and JARPA (the Japanese Whale Research Program under Special Permit in the Antarctic) vessels were engaged in the study. The main focus of the study was to elucidate the ecological interactions among biological organisms, especially between krill and whales. The surveys consisted of (1) oceanographic observations, (2) net sampling of planktons and fishes, (3) hydroacoustic surveys of krill (4) sighting surveys of top predators (birds and cetaceans) and (5) sampling of Antarctic minke whales. To understand the distribution pattern of various biological organisms in relation to oceanographic conditions, a simple oceanographic index, Mean TEMperature from the surface to 200 m (MTEM-200) was introduced. Species compositions changed against the north-south gradient of MTEM-200. For instance, Antarctic krill were mainly distributed in waters between 0 and -1ºC while ice krill were distributed in waters colder than -1ºC. Humpback whales were mainly distributed in the waters warmer than 0ºC. Antarctic minke whales were mainly distributed in waters around -1ºC in a continental shelf slope frontal zone. Comparison of stomach contents of minke whales and net samples as well as results of spatial modeling suggested that oceanographic conditions played an important role in defining predator-prey relationships. The data collected through this multidisciplinary study provides vital information to understand the structure of the marine ecosystem in the Ross Sea where data are still sparse.