The topical target areas are located in the Arctic Ocean and its marginal seas, including the Bering Sea. The marine ecosystem surrounding the Arctic Ocean is complicated, and it is difficult to predict the future because "disadvantage" phenomena such as ocean acidification and "advantage" phenomena such as improving light conditions for marine organisms, respectively, are simultaneously progressing. Investigations such as observations by research vessels and satellites, culture and breeding of plankton, and marine ecosystem models are necessary to understand not only the current status but also prediction of changes in Arctic environments and the impact on the ecosystem. In this special volume, the latest research findings are reported as follows: (1) description of recent environmental changes, physical and chemical properties associated with Arctic climate change; (2) temporal changes in primary production, secondary production and lower trophic level ecosystems; (3) recent changes in behavior and distribution of higher trophic level organisms including marine mammals; (4) the physiological response of marine phyto- and zooplankton having carbonate tests on warming or freshening associated with sea-ice melting; and (5) development of a new model for marine ecosystems in the Arctic Ocean, to reproduce the primary production by using the model and to understand the response of marine ecosystems on the catastrophic environmental changes caused by rapid sea-ice reduction. These reports can be valuable for not only for understanding the current environmental changes in the Arctic Ocean but also for obtaining new predictions of marine ecosystems of both low and high trophic level organisms including fish resources in this area. The prediction of fish resources in the Arctic Ocean would contribute to the planning of not only Japanese but also international policy for fisheries. This special issue is open to all submissions within the scope of this special issue.