Pacific Species Entering the Arctic: More ‘Invasion’ Than ‘Settlement’ [Reading Science]

Population Surges in Summer, Collapses in Autumn
Unstable Ecosystem Transition Reduces Energy Efficiency

As ocean temperatures rise due to climate change, Pacific species are entering the Arctic Ocean. However, a new study has found that these species are unable to settle in the Arctic environment. While their populations surge during the summer, they rapidly disappear as autumn approaches, raising concerns that this process could actually reduce the 'energy efficiency' of the Arctic marine ecosystem.

Araon Ship Arctic Ocean Zooplankton Collection Activity. Provided by Korea Polar Research Institute

The Korea Polar Research Institute announced on January 22 that zooplankton communities in the northwestern Arctic Ocean undergo a dramatic reorganization as the seasons shift from summer to autumn. The institute confirmed an 'unstable seasonal transition,' during which Pacific invasive species fail to adapt to the Arctic environment and are replaced by smaller species.

The research team analyzed marine environmental data collected over 14 years, from 2008 to 2021, by South Korea’s icebreaker research vessel Aron and Japan’s research vessel Mirai in the northwestern Arctic Ocean. The results showed that, during August, the influx of Pacific seawater led to a marked increase in Pacific species. In some years, larvae of warm-water cap snails were even observed expanding into the central Arctic Ocean.

Schematic Diagram of the Research Area and Research Results in the Northwestern Arctic Ocean (Created Using Google Generative AI). Provided by the Korea Polar Research Institute

However, these changes quickly disappeared as early September and autumn arrived. The researchers interpreted this as evidence that invasive species, which are sensitive to temperature and environmental changes, cannot withstand the Arctic’s rapid seasonal transition and thus fail to become established. The team explained, “The influx of Pacific species into the Arctic is closer to ‘invasion’ rather than reaching the stage of ‘settlement.’”

The bigger issue is the qualitative change in the ecosystem. Although the influx of invasive species increased overall population numbers, these species are smaller and have lower fat content compared to native Arctic species, resulting in lower energy efficiency as energy is transferred up the food web. This means that an increase in population does not necessarily translate into greater ecosystem productivity.

Schematic of the research area and research results in the Western Arctic Ocean. Provided by the Korea Polar Research Institute

Kim Jihun, the lead author of the paper, stated, “If species with low energy density become dominant, it could affect the survival of top predators such as whales and seals, which require high-calorie intake. The unstable seasonal transition in the northwestern Arctic Ocean signals a structural change in the entire Arctic food web.”

This study was conducted as part of a Ministry of Oceans and Fisheries R&D project, and the results were published in the January issue of the international journal Progress in Oceanography. Shin Hyungchul, Director of the Korea Polar Research Institute, remarked, “This is the first case of identifying the unstable changes in the Arctic ecosystem by integrating data from Korean and Japanese research vessels. It will serve as an important scientific basis for developing future strategies for the utilization and management of Arctic marine resources.”