Effects of climatic regime shift on the structure of marine ecosystem in the southwestern East Sea during the 1970s

摘要

The changes in structure and abundance of taxon or species groups in the East Sea ecosystem were compared between pre- and post-Climatic Regime Shift (CRS) occurred in the mid 1970s using an ECOPATH model. Although the East Sea ecosystem consisted of primary producers, primary consumers, secondary consumers and terminal consumers, most species groups were classified as secondary consumers. The mean trophic level between pre- and post-CRS increased from 3.09 during the pre-CRS period to 3.28 duringthe post-CRS period. Total biomass of the species groups in the East Sea ecosystem increased by 9 percent due to the CRS, and total catch increased by 48 percent. The most significant differences between pre- and post-CRS models occurred at the mid/hightrophic levels occupied by fishes and cephalopods. Relative contribution of the different species groups to the total energy flow was calculated for the trophic level III. As a result, the status by the dominant species in the East Sea ecosystem shiftedfrom cephalopods to walleye pollock due to the CRS. Relative contribution of 5 species, which were commercially important, such as Pacific saury, Pacific sardine, filefish, walleye pollock and sandfish in trophic level III, were also changed due to the CRS.Finally, the CRS turned out to cause large variations in biomass and catch of fisheries resources as well as the status and role of the major species.