17:15 〜 19:15
[ACG52-P04] Distribution and habitat preference of two cod species in the Pacific Arctic inferred from environmental DNA
キーワード：ホッキョクダラ、コマイ、環境DNA、チュクチ海
The northward shift of fish distributions in the Arctic Ocean is one of the most prominent phenomena associated with recent global warming and sea ice decline. In the Bering and Chukchi Seas, the distribution of Arctic cod (Boreogadus saida) has retracted with increasing water temperature, while the distribution of walleye pollock (Gadus chalcogrammus) and saffron cod (Eleginus gracilis) has expanded northward. As these cod species are dominant components of the fish community in the Arctic ecosystem, accurate description of their distribution shifts through spatially and temporally dense monitoring is essential to understand the cascading effects that potentially modify the Arctic ecosystem.
Environmental DNA (eDNA), a promising approach in marine biodiversity research, can scale the ability to capture the fish distribution in the Arctic Ocean. This study aimed to estimate the distribution of polar cod and saffron cod in the Pacific Arctic during the ice-free period using eDNA methodology and to clarify the habitat preferences of both species.
eDNA sampling was conducted during the R/V Mirai (Japan Agency for Marine-Earth Science and Technology) cruise in September–October 2020–2023 and the T/S Oshoro-Maru (Hokkaido University) cruise in June of 2023. All sampling sites were located in the ice-free area of the Bering and Chukchi Seas. To collect eDNA samples, surface seawater or seawater in the water column was filtered through a cartridge filter. Water temperature, salinity, and chlorophyll-a fluorescence were measured by CTD or a ship-borne monitoring system. Polar cod and saffron cod eDNA was quantified using species-specific qPCR assays. Concentrations of eDNA were visualized horizontally and vertically in juxtaposition with environmental parameters. Habitat preferences of both species were assessed using a generalized additive model (GAM).
Polar cod eDNA was exclusively detected in the Chukchi Sea. The distribution of their eDNA showed a clear tendency to concentrate in the waters around the Barrow Canyon in the northeastern part of the Chukchi Sea, while it was detected sparsely in the central part of the Chukchi Sea shelf and the basin area. Regardless of the annual fluctuations in the sea ice extent, this trend was consistently found in all years. Disparity in the vertical eDNA distribution indicated that polar cod seemingly avoided warmer water masses. The GAM indicated that water temperature, salinity, chlorophyll-a fluorescence, and distance from the shore influenced eDNA concentration. The smooth function for water temperature exhibited a unimodal shape with a maximum around 4°C, implying that polar cod preferred an environment that potentially related to the Bering-Chukchi Summer Water.
Unlike polar cod eDNA, saffron cod eDNA was mainly detected around the Bering Strait and the central part of the Chukchi Sea shelf, while it was merely detected in the basin area. The detection frequency and concentration tended to be higher in the surface layer than in the middle and bottom layers. The GAM indicated that water temperature, salinity, and chlorophyll-a fluorescence influenced eDNA concentration. The smooth functions showed a monotonic increase for water temperature and chlorophyll-a fluorescence, but a monotonic decrease for salinity. This suggests that saffron cod preferred an environment with warmer water, lower salinity, and higher primary production within the study area, which is potentially related to the Alaska Coastal Water.
This study successfully provided baseline data regarding the horizontal and vertical distribution of polar cod and saffron cod across the vast range of the Pacific Arctic, from the Bering Sea to the Chukchi Sea, and their habitat preferences. Chronologically accumulating eDNA data based on this study will be a valuable contribution for constructing a species distribution model for projecting the distribution shift of fish associated with global warming in the Arctic.
Environmental DNA (eDNA), a promising approach in marine biodiversity research, can scale the ability to capture the fish distribution in the Arctic Ocean. This study aimed to estimate the distribution of polar cod and saffron cod in the Pacific Arctic during the ice-free period using eDNA methodology and to clarify the habitat preferences of both species.
eDNA sampling was conducted during the R/V Mirai (Japan Agency for Marine-Earth Science and Technology) cruise in September–October 2020–2023 and the T/S Oshoro-Maru (Hokkaido University) cruise in June of 2023. All sampling sites were located in the ice-free area of the Bering and Chukchi Seas. To collect eDNA samples, surface seawater or seawater in the water column was filtered through a cartridge filter. Water temperature, salinity, and chlorophyll-a fluorescence were measured by CTD or a ship-borne monitoring system. Polar cod and saffron cod eDNA was quantified using species-specific qPCR assays. Concentrations of eDNA were visualized horizontally and vertically in juxtaposition with environmental parameters. Habitat preferences of both species were assessed using a generalized additive model (GAM).
Polar cod eDNA was exclusively detected in the Chukchi Sea. The distribution of their eDNA showed a clear tendency to concentrate in the waters around the Barrow Canyon in the northeastern part of the Chukchi Sea, while it was detected sparsely in the central part of the Chukchi Sea shelf and the basin area. Regardless of the annual fluctuations in the sea ice extent, this trend was consistently found in all years. Disparity in the vertical eDNA distribution indicated that polar cod seemingly avoided warmer water masses. The GAM indicated that water temperature, salinity, chlorophyll-a fluorescence, and distance from the shore influenced eDNA concentration. The smooth function for water temperature exhibited a unimodal shape with a maximum around 4°C, implying that polar cod preferred an environment that potentially related to the Bering-Chukchi Summer Water.
Unlike polar cod eDNA, saffron cod eDNA was mainly detected around the Bering Strait and the central part of the Chukchi Sea shelf, while it was merely detected in the basin area. The detection frequency and concentration tended to be higher in the surface layer than in the middle and bottom layers. The GAM indicated that water temperature, salinity, and chlorophyll-a fluorescence influenced eDNA concentration. The smooth functions showed a monotonic increase for water temperature and chlorophyll-a fluorescence, but a monotonic decrease for salinity. This suggests that saffron cod preferred an environment with warmer water, lower salinity, and higher primary production within the study area, which is potentially related to the Alaska Coastal Water.
This study successfully provided baseline data regarding the horizontal and vertical distribution of polar cod and saffron cod across the vast range of the Pacific Arctic, from the Bering Sea to the Chukchi Sea, and their habitat preferences. Chronologically accumulating eDNA data based on this study will be a valuable contribution for constructing a species distribution model for projecting the distribution shift of fish associated with global warming in the Arctic.